Evaluation method for oil paper insulation damp state of multi-element mixed insulating oil transformer

Abstract

The invention is suitable for the technical field of oil paper insulation damp state evaluation, and provides a multi-element mixed insulating oil transformer oil paper insulation damp state evaluation method, which comprises the following steps: acquiring a multi-element mixed insulating oil impregnated paper sample to be evaluated, and placing the sample in a three-electrode device; the method comprises the following steps: under a constant temperature condition, applying multi-stage alternating voltage to a sample through a frequency domain dielectric response tester, measuring dielectric loss values under different frequencies, and generating a frequency domain dielectric spectrum characteristic curve; based on the frequency domain dielectric spectrum characteristic curve, extracting a dielectric loss value corresponding to the preset characteristic frequency point as a damp characteristic parameter; inputting the damping characteristic parameter into a pre-stored damping evaluation model, wherein the model comprises a nonlinear fitting function of the dielectric loss value of a preset characteristic frequency point and the water content; and according to the water content value output by the nonlinear fitting function, generating a damp state evaluation result. According to the invention, the evaluation precision of the damp state of the multi-element mixed insulating oil impregnated paper is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil-paper insulation moisture state evaluation, and particularly relates to a method for evaluating the moisture state of oil-paper insulation of a multi-element mixed insulation oil transformer. BACKGROUND

[0002] As the core equipment of the power grid system, the liquid-solid combined oil-paper insulation system is the main technology of the power transformer, and its insulation performance is closely related to the service life of the power transformer. The oil-paper insulation system, as the main insulation structure of the oil-immersed paper transformer, has long been affected by the moisture problem in the field of power operation and maintenance. According to statistics, the insulation moisture causes more than 23% of the unplanned shutdown accidents of transformers, and the breakdown probability of the moisture insulation system under overvoltage impact is 5-8 times higher than that of the normal state. Compared with traditional mineral oil, multi-element mixed insulation oil has significant advantages in environmental protection, dielectric performance and insulation life regulation.

[0003] At present, the research on the moisture state evaluation of transformer oil-paper insulation mainly adopts the recovery voltage method or the polarization / de-polarization current method, which requires offline detection and takes a long time, and cannot meet the real-time monitoring demand of the smart grid. In addition, due to the synergistic effect of ester and hydrocarbon substances in the multi-element mixed insulation oil, the water diffusion dynamics of the oil-paper system will change, and the traditional frequency domain dielectric spectrum method has significant limitations in the multi-element mixed insulation oil scene. The frequency recognition degree of the overlapping characteristic frequency of the ester-mineral oil multi-component relaxation peak in the mixed oil decreases, which leads to the problem of deviation in the evaluation result.

[0004] In view of this, a method for evaluating the moisture state of the oil-paper insulation of a multi-element mixed insulation oil transformer is provided. SUMMARY

[0005] The present application provides a method for evaluating the moisture state of the oil-paper insulation of a multi-element mixed insulation oil transformer, which solves the problem of deviation in the moisture evaluation result.

[0006] The present application provides a method for evaluating the moisture state of the oil-paper insulation of a multi-element mixed insulation oil transformer, which includes:

[0007] Obtain a multi-element mixed insulation oil-immersed paper sample to be evaluated and place it in a three-electrode device of a frequency domain dielectric response test platform;

[0008] Under constant temperature conditions, apply a multi-level alternating voltage to the sample through a frequency domain dielectric response tester, measure the dielectric loss value under different frequencies, and generate a frequency domain dielectric spectrum characteristic curve;

[0009] Extract the dielectric loss value corresponding to the preset characteristic frequency point as a moisture characteristic parameter based on the frequency domain dielectric spectrum characteristic curve;

[0010] inputting the dampness characteristic parameter into a pre-stored dampness evaluation model, the pre-stored dampness evaluation model being established based on standard sample data of different moisture absorption durations under multi-stage alternating voltages, and containing a nonlinear fitting function of the dielectric loss value of the medium at the preset characteristic frequency point and the moisture content;

[0011] outputting a moisture content value according to the nonlinear fitting function, and generating a dampness state evaluation result of the multi-element mixed insulating oil-impregnated paper sample to be evaluated.

[0012] Further, under the constant temperature condition, the sample is subjected to multi-stage alternating voltages by a frequency domain dielectric response tester, and the dielectric loss values at different frequencies are measured to generate a frequency domain dielectric spectrum characteristic curve, which includes:

[0013] under the constant temperature condition, the multi-stage alternating voltages are applied in turn in the order of voltage rise;

[0014] the dielectric loss values under each voltage are obtained by sweeping frequency measurement of the frequency domain dielectric response tester in a preset frequency range;

[0015] after the measurement of each voltage is completed, the sample is subjected to discharge treatment;

[0016] the above steps are repeated until the measurement of all voltage levels is completed, and the frequency domain dielectric spectrum characteristic curve containing multi-stage voltages is generated.

[0017] Further, the multi-stage alternating voltages contain at least two voltage segments, and the voltage value of the highest voltage segment is not less than 5000V.

[0018] Further, the dielectric loss value corresponding to the preset characteristic frequency point is extracted based on the frequency domain dielectric spectrum characteristic curve as the dampness characteristic parameter, which includes:

[0019] the dielectric loss values corresponding to three frequency points of 10 -1 Hz, 10 0 Hz and 10 1 Hz are read from the frequency domain dielectric spectrum characteristic curve;

[0020] if a certain frequency point does not exist directly in the measurement data, the dielectric loss value of the certain frequency point is obtained by linear interpolation calculation of the dielectric loss values of adjacent frequency points.

[0021] Further, the calculation formula of the dielectric loss value includes:

[0022]

[0023] wherein tanδ is a dielectric loss factor, ε″ r is a real part of a complex dielectric constant, corresponding to a capacitance term, and ε′ rFor the imaginary part of the complex dielectric constant, the corresponding point to the loss term of the component.

[0024] Further, the pre-stored moisture evaluation model is established based on standard sample data of different moisture absorption durations under multi-level alternating voltages, and includes:

[0025] By controlling the moisture absorption duration, standard samples of multi-component mixed insulation oil-impregnated paper with different water contents are obtained, wherein the water content of the standard samples covers from the dry state to the severely moist state.

[0026] A multi-level alternating voltage is applied to each group of standard samples, and the dielectric loss value of the standard samples at the preset characteristic frequency point is measured.

[0027] The dielectric loss value and the measured water content of the corresponding standard sample are subjected to regression analysis to construct a nonlinear fitting function with the dielectric loss value at the characteristic frequency point as the input variable and the water content as the output variable.

[0028] The test data of the independent verification sample are used to verify whether the evaluation error of the nonlinear fitting function is less than a preset threshold.

[0029] Further, the nonlinear fitting function is a three-parameter exponential function established for the dielectric loss value at each preset characteristic frequency point, and the coefficient of the exponential term of the function is determined by fitting the standard sample data.

[0030] Further, the moisture content value output by the nonlinear fitting function is used to generate the moisture state evaluation result of the multi-component mixed insulation oil-impregnated paper sample to be evaluated, including:

[0031] The voltage grade of the transformer corresponding to the multi-component mixed insulation oil-impregnated paper sample to be evaluated is obtained.

[0032] According to the voltage grade, a corresponding water content limit value is selected, and the moisture content value output by the nonlinear fitting function is compared with the limit value to determine the moisture state evaluation result.

[0033] Further, the comparison of the moisture content value output by the nonlinear fitting function with the limit value to determine the moisture state evaluation result includes:

[0034] If the moisture content value exceeds the limit value, it is determined that the moisture state is unqualified, otherwise it is determined that the moisture state is qualified.

[0035] From the above technical solutions, the present application has the following advantages:

[0036] The application utilizes a frequency domain dielectric response test platform to measure the dielectric loss value of the sample at different frequencies after obtaining the sample to be evaluated, generates the corresponding frequency domain dielectric spectrum characteristic curve, extracts the dielectric loss value of the preset characteristic frequency point as the moisture absorption characteristic parameter, inputs the moisture absorption characteristic parameter into the pre-stored moisture absorption evaluation model for evaluation, outputs the sample water content value based on the nonlinear fitting function of the model, and finally generates the corresponding moisture absorption state evaluation result. The application extracts the dielectric characteristic parameters of the multi-element mixed insulation oil immersed paper by high-voltage wide-band excitation, constructs a moisture absorption state evaluation model of the multi-element mixed insulation oil immersed paper, effectively improves the evaluation accuracy of the moisture absorption state of the multi-element mixed insulation oil immersed paper, and provides a standardized technical framework for the state monitoring of the multi-element mixed insulation oil transformer. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is an embodiment flow schematic diagram of the moisture absorption state evaluation method of the multi-element mixed insulation oil transformer oil paper insulation in the application;

[0038] Figure 2 It is a structural schematic diagram of the frequency domain dielectric response test platform in the application;

[0039] Figure 3 It is a schematic diagram of the frequency domain dielectric response characteristics of the dry multi-element mixed insulation oil immersed paper in the application;

[0040] Figure 4 It is a schematic diagram of the frequency domain dielectric response characteristics of the multi-element mixed insulation oil immersed paper with a water content of 1.49% in the application;

[0041] Figure 5 It is a schematic diagram of the frequency domain dielectric response characteristics of the multi-element mixed insulation oil immersed paper with a water content of 2.33% in the application;

[0042] Figure 6 It is a schematic diagram of the frequency domain dielectric response characteristics of the multi-element mixed insulation oil immersed paper with a water content of 3.31% in the application;

[0043] Figure 7 It is a schematic diagram of the frequency domain dielectric response characteristics of the multi-element mixed insulation oil immersed paper with a water content of 4.28% in the application;

[0044] Figure 8 It is a characteristic frequency point dielectric loss value fitting curve diagram of the multi-element mixed insulation oil immersed paper with different applied voltages and water contents in the application;

[0045] Figure 9 It is a measured dielectric loss curve diagram of the multi-element mixed insulation oil immersed paper sample to be evaluated in the application. DETAILED DESCRIPTION

[0046] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "corresponding to" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0047] Example 1

[0048] The implementation method in this embodiment can be implemented in the system, can be implemented in the server, and can also be implemented in the terminal, and the specific implementation is not clearly limited. The following is an introduction to the method for evaluating the moisture state of the oil-paper insulation of the multi-component mixed insulating oil transformer in this application from the perspective of system implementation. Figure 1 , the method provided in the embodiment of the present application includes the following steps:

[0049] S11. Obtain a sample of the multicomponent hybrid insulating oil-impregnated paper to be evaluated and place it in a three-electrode device on the frequency-domain dielectric response test platform.

[0050] In this example, after obtaining the multi-component mixed insulating oil-impregnated paper sample to be evaluated, the surface must first be cleaned to ensure that there are no oil stains or impurities. The sample is then cut into a circular test piece with a diameter of 160 mm and a thickness of 1 mm to match the dimensions of the three-electrode apparatus. Samples with a high initial moisture content must be pretreated in a vacuum drying oven (90°C, 50 Pa) for 48 hours to remove free surface moisture and ensure consistency of the test benchmark.

[0051] Place the pretreated sample in the three-electrode device of the frequency domain dielectric response test platform, see Figure 2The frequency domain dielectric response test platform comprises an IDAX-300 frequency domain dielectric response tester, a voltage amplifier, a three-electrode device and a PC control terminal; wherein the output voltage range of the IDAX-300 frequency domain dielectric response tester is sinusoidal alternating current 0-200V, and the output frequency range is 0.1mHz-10kHz; the amplification multiple of the voltage amplifier is 1000 times, the input voltage peak value range is alternating current 0-10V, and the output voltage peak value range is alternating current 0-10kV; the diameter of the high-voltage electrode of the three-electrode device is 130mm, and the diameter of the measuring electrode is 97.8mm. The measurement voltages are 200V, 1000V, 2500V, 5000V and 7000V, the measurement frequency range is 1mHz to 100Hz, the test room temperature is 40℃, and each test is discharged for 10min to release residual charge and ensure that each group of tests does not affect each other.

[0052] It should be noted that the moisture state evaluation method of the present application is adapted to a multi-component mixed insulating oil system composed of 65vol.% 25# naphthenic mineral oil, 10vol.% soybean oil, 20vol.% ethyl hexyl laurate, 5vol.% isooctyl laurate and 0.4wt.% antioxidant.

[0053] S12. Under constant temperature conditions, a multi-level alternating voltage is applied to the sample by the frequency domain dielectric response tester, the dielectric loss values at different frequencies are measured, and a frequency domain dielectric spectrum characteristic curve is generated;

[0054] Step S12 comprises the following:

[0055] 1. Under constant temperature conditions, a multi-level alternating voltage is applied in turn according to the voltage ascending order;

[0056] 2. The frequency domain dielectric response tester is used to perform sweep frequency measurement at a preset frequency range to obtain the dielectric loss value under each voltage level;

[0057] 3. After the measurement of each voltage level is completed, the sample is discharged;

[0058] 4. The above steps are repeated until the measurement of all voltage levels is completed, and a frequency domain dielectric spectrum characteristic curve containing multi-level voltages is generated.

[0059] Specifically, the multi-level alternating voltage comprises at least two voltage segments, and the voltage value of the highest voltage segment is not less than 5000V.

[0060] The above steps are described in detail as follows:

[0061] The test is carried out in a thermostat, the temperature is constant at 40±2℃, the humidity is controlled below 30%, and the environmental temperature and humidity fluctuations are avoided to interfere with the dielectric properties. A plurality of AC voltages are applied in turn in ascending order of voltage, specifically including 200V, 1000V, 2500V, 5000V and 7000V (the highest voltage segment is ≥5000V). The application time of each voltage is 5-10 minutes to ensure that the polarization process is fully stable; the IDAX-300 frequency domain dielectric response tester is used to perform linear or logarithmic sweep in the range of 1mHz to 100Hz, and the frequency step interval is 10% change rate, for example, from 1mHz to 10mHz, which is increased by logarithmic interval.

[0062] At each voltage level, the complex dielectric constant at each frequency point is recorded in real time, and the dielectric loss factor is calculated; after completing each voltage measurement, the power is turned off and the sample is discharged; after standing for 10 minutes, the residual charge is released by using the insulation resistance of the sample itself; the electrodes are short-circuited through the grounding device to accelerate the charge dissipation and ensure that the next voltage test is not disturbed by the residual charge. Finally, all the measurement data under different voltage levels are integrated to generate the frequency domain dielectric spectrum characteristic curve of multiple voltages. Each curve contains the real part of the capacitance, the dielectric loss factor, and the law of dielectric response varying with frequency under different voltages.

[0063] S13. Based on the frequency domain dielectric spectrum characteristic curve, the dielectric loss value corresponding to the preset characteristic frequency point is extracted as the moisture characteristic parameter;

[0064] In this embodiment, the preset characteristic frequency points include three discrete frequency points in the low frequency band, the medium frequency band and the high frequency band, specifically 10 -1 Hz, 10 0 Hz and 10 1 Hz. The following will explain how to determine the preset characteristic frequency points in combination with the specific experimental process:

[0065] 1. First, prepare multiple-element mixed insulating oil-impregnated papers in different moisture states, cut multiple circular insulating paper boards with a thickness of 1mm and a diameter of 160mm, place the circular insulating paper boards and the multiple-element mixed insulating oil into a vacuum drying box, and vacuum dry for 48h (90℃, 50Pa). The vacuum-dried insulating paper boards are immersed in dry multiple-element mixed insulating oil and placed in a vacuum drying box (90℃, 50Pa) for 48h to obtain dry multiple-element mixed insulating oil-impregnated paper as a control sample. Then, the surface of the multiple-element mixed insulating oil-impregnated paper is wiped dry, and the initial water content of the dry multiple-element mixed insulating oil-impregnated paper is measured by a Karl Fischer titrator and the weight at this time is recorded. Finally, the multiple-element mixed insulating oil-impregnated paper is respectively placed in air to naturally absorb moisture for 5h, 10h, 15h and 20h (air temperature 20℃, relative humidity 80%), to obtain four groups of samples in different moisture states, and the water content of each sample is shown in Table 1:

[0066] Table 1 Different moisture content of multi-component mixed insulation oil-impregnated paper

[0067] Moisture exposed sample Moisture content Control sample (dry) 0.78％ Moisture exposed sample 1 (moisture exposure 5h) 1.49％ Moisture exposed sample 2 (moisture exposure 10h) 2.33％ Moisture exposed sample 3 (moisture exposure 15h) 3.31％ Moisture exposed sample (moisture exposure 20h) 4.28％

[0068] The frequency domain dielectric spectrum characteristics curves of the samples with different moisture contents at multiple voltage levels were measured by experiments. The samples with dry, 5h, 10h, 15h and 20h moisture absorption were selected, and multiple voltage levels were set as 200V, 1000V, 2500V, 5000V and 7000V. The law of the change of the dielectric loss factor with frequency was analyzed, as shown in Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 and Figure 7 , the real part of the capacitance of the multi-component mixed insulation oil-impregnated paper decreases in the whole frequency band with the increase of the applied voltage. In addition, the degree of change of the real part of the capacitance of the multi-component mixed insulation oil-impregnated paper with the applied voltage is significantly higher than that of the dry control sample with a water content of 4.28%, indicating that the increase of the water content can increase the sensitivity of the real part of the capacitance of the multi-component mixed insulation oil-impregnated paper to the voltage. On the other hand, the dielectric loss frequency of the dry control sample shows different performance laws at different voltages. When the applied voltage is low (200V, 1000V, 2500V), the dielectric loss spectrum increases with the increase of the frequency at 1mHz-4.6mHz, and there is an obvious loss peak, while when the applied voltage is high (5000V, 7000V), the loss peak disappears, indicating that the conductive loss increases significantly with the increase of the applied voltage, which masks the information of other polarization losses. With the increase of the applied voltage, the dielectric loss spectrum of the multi-component mixed insulation oil-impregnated paper with a water content of 4.28% increases significantly, and the frequency corresponding to the loss peak moves to low frequency. With the increase of the applied voltage, the imaginary part of the capacitance of the multi-component mixed insulation oil-impregnated paper decreases, and the dielectric loss curve increases. The voltage has a great influence on the tanδ value of the multi-component mixed insulation oil-impregnated paper, and the calculation formula of the dielectric loss value is wherein tanδ is the dielectric loss factor, ε″ r is the real part of the complex dielectric constant, corresponding to the capacitance term, ε′ r is the imaginary part of the complex dielectric constant, corresponding to the loss term of the point to component, and Figure 4 (b) is taken as an example, the tanδ at 1mHz under 200V and 7000V is 4.17 and 51.4 respectively, which increases by about 11.3 times.

[0069] From the influence law of the water content on the dielectric loss curve of the multi-component mixed insulation oil-impregnated paper under different voltages in Figures 3-7 , the dielectric loss values at the three characteristic frequency points of 10 -1 Hz, 10 0 Hz and 10 1 Hz are very sensitive to the change of water, therefore, 10 -1 Hz, 100 Hz and 10 1 Hz, the dielectric loss values of the three discrete frequency points are directly taken as the characterization parameters of the water content.

[0070] In this embodiment, the dielectric loss value corresponding to the preset characteristic frequency point is extracted, including:

[0071] 1. The dielectric loss values of 10 -1 Hz, 10 0 Hz and 10 1 Hz are read from the frequency domain dielectric spectrum characteristic curve;

[0072] 2. If a certain frequency point does not exist directly in the measured data, the dielectric loss value of the certain frequency point is obtained by linear interpolation calculation of the dielectric loss values of adjacent frequency points.

[0073] First, the dielectric loss values of 10 -1 Hz, 10 0 Hz and 10 1 Hz are directly obtained from the frequency domain dielectric spectrum characteristic curve; if a certain frequency point is not directly measured, the dielectric loss value of the certain frequency point is calculated by linear interpolation of the measured dielectric loss values of adjacent frequency points, to ensure the data integrity and consistency of all preset characteristic frequency points. This step solves the problem of missing parameters caused by frequency point discretization in actual measurement by combining direct data reading and interpolation compensation.

[0074] S14. Input the moisture characteristic parameter into the pre-stored moisture evaluation model, the pre-stored moisture evaluation model is established based on standard sample data of different moisture absorption time under multi-level alternating voltage, and includes a nonlinear fitting function of the dielectric loss value of the preset characteristic frequency point and the water content;

[0075] In this embodiment, the pre-stored moisture evaluation model established based on standard sample data of different moisture absorption time under multi-level alternating voltage includes the following steps:

[0076] 1. Obtain multi-element mixed insulating oil immersed paper standard samples with different water contents by controlling the moisture absorption time, wherein the water content of the standard sample covers from dry state to serious moisture state;

[0077] 2. Apply multi-level alternating voltage to each group of standard samples, and measure the dielectric loss value of the standard sample at the preset characteristic frequency point;

[0078] 3. Perform regression analysis on the dielectric loss value and the measured water content of the corresponding standard sample, and construct a nonlinear fitting function taking the characteristic frequency point dielectric loss value as the input variable and the water content as the output variable;

[0079] 4. Verify whether the evaluation error of the nonlinear fitting function is less than a preset threshold value by testing data of an independent verification sample.

[0080] The above steps define the model building process. First, standard samples covering dry (0.78%) to severely damp (4.28%) are prepared by controlling the moisture absorption time. Then, the dielectric loss values at preset characteristic frequency points are measured under multi-level alternating voltages (200V-7000V), and a nonlinear fitting function with dielectric loss value as input and moisture content as output is constructed by regression analysis. The nonlinear fitting function is a three-parameter exponential function established for the dielectric loss value at each preset characteristic frequency point, and the exponential term coefficient of the function is determined by fitting the standard sample data. Finally, the model error is verified by independent verification samples such as 1.61% and 3.33% moisture content samples, and the preset threshold is set to 10% to ensure the reliability of the evaluation.

[0081] Based on the above step S13, 10 -1 Hz, 10 0 Hz and 10 1 Hz three frequency points are very sensitive to moisture changes, and are used as moisture content characterization parameters. The dielectric loss values at the characteristic frequency points under different applied voltages and moisture contents are shown in Table 1, and the measured values and fitting curves are shown in Figure 8 The results show that the moisture content of the multi-component mixed insulation oil-impregnated paper increases exponentially with the dielectric loss values at the three characteristic frequency points under different applied voltages. With the increase of voltage, the dielectric loss values at the characteristic frequency points increase significantly. Under the condition of 200V, the dielectric loss values at the three frequency points are all within 20, and the dielectric loss values at different frequency points coincide. With the increase of applied voltage, the difference of dielectric loss values at the three frequency points increases significantly, which is more conducive to the evaluation of the moisture content of the oil-impregnated paperboard. The fitting formula corresponding to each voltage and characteristic frequency point in Table 2 is the evaluation model of the dielectric loss value at the characteristic frequency point of the oil-impregnated paperboard under the condition of voltage and characteristic frequency point. Based on this function model, the moisture content of the oil-impregnated paperboard can be evaluated.

[0082] Table 2 Dielectric loss values at characteristic frequency points of multi-component mixed insulation oil-impregnated paper under different applied voltages and moisture contents

[0083]

[0084]

[0085] S15. According to the moisture content value output by the nonlinear fitting function, the moisture state evaluation result of the multi-component mixed insulation oil-impregnated paper sample to be evaluated is generated.

[0086] Step S15 includes the following:

[0087] 1. Obtain the transformer voltage grade corresponding to the multi-component mixed insulation oil-impregnated paper sample to be evaluated;

[0088] 2. Select the corresponding moisture content limit according to the voltage level, and compare the moisture content value output by the nonlinear fitting function with the limit to determine the moisture state assessment result; if the moisture content value exceeds the limit, it is judged that the moisture state is unqualified; otherwise, it is judged that the moisture state is qualified.

[0089] First, the transformer voltage level (e.g., 500kV, 330kV, or 220kV) corresponding to the sample to be evaluated is obtained. The moisture content limit specified in the industry standard (DL / T 596-2021) is dynamically selected based on the voltage level, for example, 1% for 500kV and 3% for 220kV. Finally, the moisture content value output by the nonlinear fitting function (e.g., 2.5%) is compared with the selected limit. If the moisture content exceeds the limit, such as a moisture content of >3% for a 220kV transformer, the transformer is deemed "unqualified due to moisture," requiring drying or insulation replacement. If the moisture content is within the limit, such as a moisture content of ≤1% for a 500kV transformer, the transformer is deemed "qualified due to moisture," and the equipment can operate safely.

[0090] The above embodiment is verified by experiments below:

[0091] The multi-component mixed insulating oil-impregnated paper samples with actual moisture contents of 1.61% and 3.33% were selected as the verification objects. The two samples with different moisture conditions were tested for 10 -1 Hz, 10 0 Hz and 10 1 The dielectric loss at three characteristic frequency points of Hz is statistically analyzed to evaluate the water content of the sample. Figure 9 As shown in Table 3 below, the test results show that the moisture assessment results based on the 200V measurement results are slightly smaller, and the moisture assessment results based on the 2500V and 5000V measurement results are slightly larger. However, as the measurement voltage increases, the absolute value of the error percentage decreases significantly, indicating that the moisture assessment of the multi-component hybrid insulating oil-impregnated paper under high voltage testing is more accurate, and the moisture content assessment method is basically within 10% of the measured results. Therefore, the method for assessing the moisture status of the oil-paper insulation of the multi-component hybrid insulating oil transformer of the present invention is reliable and effective, and can provide technical support for the operational health monitoring of multi-component hybrid insulating oil transformers.

[0092] Table 3 Dielectric loss values ​​at characteristic frequency points and moisture evaluation results of the multi-component mixed insulating oil-impregnated paper samples to be evaluated

[0093]

[0094] The above embodiment is based on the multi-component mixed insulating oil impregnated paper under high voltage excitation 10 -3 -10 2The application is characterized in that the dielectric response data of the wide frequency band of 1-1000 kHz is obtained, a moisture state evaluation model is established by fitting a function of the extracted dielectric characteristic parameters, and a high-precision moisture state of the multi-component mixed insulating oil impregnated paper is evaluated, thereby providing a standardized technical framework for the state monitoring of the multi-component mixed insulating oil transformer.

[0095] It can be understood that those skilled in the art can combine various embodiments in the above embodiments to obtain various embodiments of the technical solutions.

[0096] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement and improvement within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for evaluating the moisture status of oil-paper insulation in a multi-component mixed insulating oil transformer, characterized in that: include: Obtain a multi-component hybrid insulating oil-impregnated paper sample to be evaluated and place it in a three-electrode device of a frequency domain dielectric response test platform; Under constant temperature conditions, a frequency domain dielectric response tester is used to apply multi-level AC voltage to the sample, measure the dielectric loss values ​​at different frequencies, and generate a frequency domain dielectric spectrum characteristic curve; Extracting a dielectric loss value corresponding to a preset characteristic frequency point based on the frequency domain dielectric spectrum characteristic curve as a moisture characteristic parameter; Inputting the moisture characteristic parameter into a pre-stored moisture assessment model, wherein the pre-stored moisture assessment model is established based on standard sample data of different moisture absorption times under multi-level AC voltages and includes a nonlinear fitting function of the dielectric loss value and the water content at the preset characteristic frequency point; An evaluation result of the moisture state of the multi-component mixed insulating oil-impregnated paper sample to be evaluated is generated according to the moisture content value output by the nonlinear fitting function.

2. The method for evaluating the moisture state of oil-paper insulation of a multi-component mixed insulating oil transformer according to claim 1, characterized in that: Under constant temperature conditions, a multi-level AC voltage is applied to the sample by a frequency domain dielectric response tester to measure the dielectric loss values ​​at different frequencies and generate a frequency domain dielectric spectrum characteristic curve, including: Under constant temperature conditions, multiple levels of AC voltage are applied in ascending order of voltage; Use a frequency domain dielectric response tester to perform sweep measurements within a preset frequency range to obtain the dielectric loss value at each voltage level; After completing each level of voltage measurement, the sample is discharged; Repeat the above steps until all voltage levels are measured, and generate a frequency domain dielectric spectrum characteristic curve containing multiple voltage levels.

3. The method for evaluating the moisture state of oil-paper insulation of a multi-component mixed insulating oil transformer according to claim 2, characterized in that: The multi-level AC voltage includes at least two voltage segments, wherein the voltage value of the highest voltage segment is not less than 5000V.

4. The method for evaluating the moisture state of oil-paper insulation of a multi-component mixed insulating oil transformer according to claim 1, characterized in that: The preset characteristic frequency points include three discrete frequency points in the low frequency band, the middle frequency band and the high frequency band, specifically 10 - 1 Hz, 10 0 Hz and 10 1 Hz.

5. The method for evaluating the moisture state of oil-paper insulation of a multi-component mixed insulating oil transformer according to claim 4, characterized in that: The step of extracting the dielectric loss value corresponding to a preset characteristic frequency point based on the frequency domain dielectric spectrum characteristic curve as a moisture characteristic parameter includes: Read 10 from the frequency domain dielectric spectrum characteristic curve -1 Hz, 10 0 Hz and 10 1 The dielectric loss values ​​corresponding to the three frequency points of Hz; If a certain frequency point does not directly exist in the measurement data, the dielectric loss value of the certain frequency point is obtained by performing linear interpolation calculation through the dielectric loss values ​​of adjacent frequency points.

6. The method for evaluating the moisture state of oil-paper insulation of a multi-component mixed insulating oil transformer according to claim 5, characterized in that: The calculation formula of the dielectric loss value includes: Where: tanδ is the dielectric loss factor, ε″ r is the real part of the complex dielectric constant, corresponding to the capacitance term, ε′ r is the imaginary part of the complex dielectric constant, corresponding to the point-to-component loss term.

7. The method for evaluating the moisture state of oil-paper insulation of a multi-component mixed insulating oil transformer according to claim 1, characterized in that: The pre-stored moisture assessment model is established based on standard sample data of different moisture absorption times under multi-level AC voltages, including: By controlling the moisture absorption time, standard samples of multi-component mixed insulating oil-impregnated paper with different moisture contents are obtained, where the moisture content of the standard samples ranges from dry state to severely damp state; Applying a multi-level AC voltage to each set of standard samples, and measuring the dielectric loss value of the standard samples at the preset characteristic frequency point; Performing regression analysis on the dielectric loss value and the measured water content of the corresponding standard sample to construct a nonlinear fitting function with the dielectric loss value at the characteristic frequency point as the input variable and the water content as the output variable; By independently verifying the test data of the sample, it is verified whether the evaluation error of the nonlinear fitting function is less than a preset threshold.

8. The method for evaluating the moisture state of oil-paper insulation of a multi-component mixed insulating oil transformer according to claim 7, characterized in that: The nonlinear fitting function is a three-parameter exponential function established for the dielectric loss value of each preset characteristic frequency point, and the exponential term coefficient of the function is determined by fitting standard sample data.

9. The method for evaluating the moisture state of oil-paper insulation of a multi-component mixed insulating oil transformer according to claim 1, characterized in that: The step of generating a moisture state evaluation result of the multi-component mixed insulating oil-impregnated paper sample to be evaluated according to the moisture content value output by the nonlinear fitting function includes: Obtaining the transformer voltage level corresponding to the multi-component mixed insulating oil-impregnated paper sample to be evaluated; A corresponding moisture content limit is selected according to the voltage level, and the moisture content value output by the nonlinear fitting function is compared with the limit to determine a moisture state assessment result.

10. The method for evaluating the moisture state of oil-paper insulation of a multi-component mixed insulating oil transformer according to claim 9, characterized in that: The step of comparing the water content value output by the nonlinear fitting function with the limit value to determine the moisture state assessment result includes: If the water content exceeds the limit, it is determined that the moisture state is unqualified; otherwise, it is determined that the moisture state is qualified.

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