A method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in a transformer

Abstract

The present invention provides a method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in a transformer, belonging to the field of insulation dielectric response diagnosis of oil-immersed transformers. The method includes: measuring the complex capacitance of the main insulation of the transformer and calculating its frequency-domain dielectric spectrum; measuring the complex capacitance of the insulating oil and calculating its frequency-domain dielectric spectrum; calculating the frequency-domain dielectric spectrum of the oil-impregnated paper under different insulation structure parameters according to the spectra of the main insulation and the insulating oil; using a dielectric spectrum model to fit the frequency spectra of the oil-impregnated paper calculated under different insulation structures, and the set with the minimum fitting residual is the required frequency-domain dielectric spectrum of the oil-impregnated paper. The present invention can realize obtaining the frequency-domain dielectric spectrum of the oil-impregnated paper when the parameters of the main insulation structure of the transformer are unknown, and provides a more effective means for further interpreting the dielectric information of the oil-impregnated paper and obtaining its insulation state.

Description

Technical Field

[0001] The present invention relates to the field of insulation dielectric response diagnosis of oil-immersed transformers, and specifically to a method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in a transformer. Background Art

[0002] The main insulation of an oil-immersed transformer is a typical oil-paper insulation structure. During long-term operation, due to the influence of electricity, heat, moisture, and mechanical effects, its insulation performance gradually deteriorates, posing a serious threat to the safe and stable operation of the transformer. Therefore, it is necessary to accurately and effectively diagnose the main insulation state of the transformer, which is a hot topic in the current power industry and an urgent problem to be solved. The frequency-domain spectroscopy (FDS) based on dielectric response is a non-destructive measurement method for evaluating the insulation state of electrical equipment. Due to its rich information-carrying capacity, strong anti-interference ability, and non-destructive detection characteristics, FDS is widely used in oil-containing electrical equipment, especially in the field of state evaluation of the oil-paper insulation of oil-immersed transformers.

[0003] The main insulation of the transformer is composed of oil ducts, spacers, and insulating paper cylinders, as Figure 1 shown. Its frequency-domain dielectric spectrum is affected by many factors such as insulation structure and insulating oil performance, and can generally only be used to qualitatively analyze the insulation state. The frequency-domain dielectric spectrum of oil-impregnated paper is not affected by the insulation structure and contains comprehensive insulation state information, which can be used to quantitatively analyze the insulation state of the transformer. However, in practical applications, what can be directly measured is the frequency-domain dielectric spectrum of the main insulation of the transformer. Therefore, it is necessary to extract the frequency-domain dielectric spectrum of the oil-impregnated paper from the main insulation spectrum. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in an oil-immersed transformer. According to the measured frequency-domain dielectric spectra of the main insulation and insulating oil, combined with the dielectric spectrum model, the frequency-domain dielectric spectrum of the oil-impregnated paper is obtained under the condition that the main insulation structure is unknown.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in an oil-immersed transformer, the method comprising the following steps:

[0007] S1: Measure the complex capacitance C all * (ω) of the main insulation of the transformer, and calculate the frequency-domain dielectric spectrum ε all * (ω) of the main insulation;

[0008] S2: Measure the complex capacitance C of the insulating oiloil * (ω), and calculate the frequency-domain dielectric spectrum ε of the insulating oil oil * (ω);

[0009] S3: According to the frequency-domain dielectric spectrum ε of the main insulation all * (ω) and the frequency-domain dielectric spectrum ε of the insulating oil oil * Calculate the frequency-domain dielectric spectrum ε of the oil-impregnated paper under different insulation structure parameters paper * (ω);

[0010] S4: Use the dielectric spectrum model to fit the oil-impregnated paper frequency spectrum ε paper * (ω) obtained by calculation under different insulation structures. The set with the smallest fitting residual is the required frequency-domain dielectric spectrum of the oil-impregnated paper.

[0011] Furthermore, the complex capacitances C all * (ω) and C oil * (ω) in S1 and S2 are directly measured by a dielectric impedance spectrometer. The frequency measurement range is 1 mHz - 10 kHz. The frequency-domain dielectric spectrum ε * (ω) is calculated according to the following formula:

[0012]

[0013] where ω is the angular frequency, C * (ω) is the complex capacitance of the main insulation of the transformer or the insulating oil, and C0 is the geometric capacitance of the insulation.

[0014] Furthermore, S3 specifically includes the following steps:

[0015] S31: Calculate the frequency-domain dielectric spectrum ε of the oil-impregnated paper according to the following formula paper * (ω):

[0016]

[0017] where X is the ratio of the total thickness of each layer of oil-impregnated paper in the main insulation to the spacing of the main insulation, Y is the ratio of the total width of the spacers at each place to the average perimeter of the high- and low-voltage windings, and the initial values of X and Y are both 0.1.

[0018] S32: Gradually change the values of the insulation structure parameters X and Y, and calculate ε under different structure parameters paper *(ω), the value range of X is 0.1 - 0.5, the value range of Y is 0.1 - 0.3, and the step size is 0.01 for both.

[0019] Further, the dielectric spectrum model in S4 is as follows:

[0020]

[0021] The fitting residual λ is defined as:

[0022]

[0023] where ε' 拟合 and ε' 计算 are the real parts of the complex dielectric constant obtained by fitting and calculating using the dielectric spectrum model respectively, and ε” 拟合 and ε” 计算 are the imaginary parts of the complex dielectric constant obtained by fitting and calculating using the dielectric spectrum model respectively.

[0024] Further, the basis for selecting the group with the smallest fitting residual in S4 as the solution result is: The true frequency-domain dielectric spectrum ε paper * (ω) satisfies the dielectric spectrum model described by Equation (2), and its corresponding fitting residual is very small; while the ε paper * (ω) calculated using the wrong structural parameter values of X and Y has a large difference from the true value and cannot be accurately described by Equation (2), and its corresponding fitting residual is also large. Therefore, the group with the smallest fitting residual is the true ε paper * (ω).

[0025] The beneficial effects of the present invention are as follows: A method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in a transformer provided by the present invention measures the frequency-domain dielectric spectra of the main insulation and insulating oil of the transformer, combines different insulation structure parameters to calculate the frequency-domain dielectric spectrum of the internal oil-impregnated paper, and uses the dielectric spectrum model to fit the oil-impregnated paper spectra calculated under different structures. The group with the smallest fitting residual is the required frequency-domain dielectric spectrum of the oil-impregnated paper. The present invention can obtain the frequency-domain dielectric spectrum of the oil-impregnated paper when the main insulation structure parameters of the transformer are unknown, providing a more effective means for further interpreting the dielectric information of the oil-impregnated paper and obtaining its insulation state. Description of the Drawings

[0026] Figure 1 is the main insulation model of the transformer;

[0027] Figure 2 is the measured frequency-domain dielectric spectrum of the main insulation of the transformer provided by the embodiment of the present invention;

[0028] Figure 3It is the frequency-domain dielectric spectrum of the transformer insulating oil obtained by measurement according to the embodiments of the present invention;

[0029] Figure 4 It is the frequency-domain dielectric spectrum of oil-impregnated paper obtained by calculation under different insulation structure parameters according to the embodiments of the present invention;

[0030] Figure 5 It is the residual distribution diagram of fitting the frequency-domain dielectric spectrum of oil-impregnated paper obtained by calculation with different insulation structure parameters by using a dielectric model according to the embodiments of the present invention;

[0031] Figure 6 It is the frequency-domain dielectric spectrum of the oil-impregnated paper inside the transformer obtained and the fitting curve of its dielectric model according to the embodiments of the present invention. Specific Embodiments

[0032] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] The embodiments of the present invention provide a method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in a transformer, including the following steps:

[0034] S1: Measure the complex capacitance C all * (ω) of the main insulation of the transformer, and calculate the frequency-domain dielectric spectrum ε all * (ω);

[0035] The present invention takes the main insulation model of the transformer built in the laboratory as the research object, and the insulation structure parameters are X = 0.33 and Y = 0.2, as Figure 1 shown. After building the main insulation model, seal it and evacuate it, and place the whole device in a constant temperature oven at 45°C for 48 h so that the temperature and moisture content are fully stable. Measure the frequency-domain dielectric spectrum of the main insulation, the frequency measurement range is 1 mHz - 10 kHz, the effective value of the excitation voltage is 140 V, and the measurement results are as Figure 2 shown.

[0036] S2: Measure the complex capacitance C oil * (ω) of the insulating oil, and calculate the frequency-domain dielectric spectrum ε oil * (ω);

[0037] Take oil from the main insulation model and measure its frequency-domain dielectric spectrum. The test temperature is consistent with the dielectric measurement of the main insulation, both being 45 °C. The measurement results are as Figure 3 shown.

[0038] S3: According to the frequency-domain dielectric spectra ε all * (ω) and ε oil * of the main insulation and insulating oil, calculate the frequency-domain dielectric spectrum ε paper * (ω) of oil-impregnated paper under different insulation structure parameters;

[0039] According to the measured frequency-domain dielectric spectra ε all * (ω) and ε all * of the main insulation and insulating oil, calculate the frequency-domain dielectric spectrum ε paper * (ω) of oil-impregnated paper according to the following formula.

[0040]

[0041] The value range of the insulation structure parameter X is 0.1 - 0.5, and the value range of Y is 0.1 - 0.3. The step size is 0.01 for both. A total of 861 groups of ε paper * (ω) are calculated, Figure 4 and 4 groups of the calculation results are shown.

[0042] S4: Use the dielectric spectrum model to fit the oil-impregnated paper frequency spectra obtained under different insulation structures. The group with the smallest fitting residual is the desired frequency-domain dielectric spectrum of the oil-impregnated paper.

[0043] Use the dielectric spectrum model formula (2) to fit the 861 groups of frequency-domain dielectric spectra of oil-impregnated paper obtained under different insulation structure parameters:

[0044]

[0045] And calculate the fitting residual λ of each group of frequency-domain dielectric spectra of oil-impregnated paper according to formula (3):

[0046]

[0047] Figure 5 The distribution diagram of the fitting residuals of the 861 groups of frequency-domain dielectric spectra of oil-impregnated paper obtained under different insulation structure parameters is shown. When the structure parameters X = 0.34 and Y = 0.19 are taken, the fitting residual is the smallest, and the corresponding calculated frequency-domain dielectric spectrum of the oil-impregnated paper is the desired one. Figure 6 The obtained frequency-domain dielectric spectrum of the oil-impregnated paper and its fitting curve of the dielectric spectrum model are shown.

[0048] The beneficial effects of the present invention are as follows. Compared with the prior art, the present invention can obtain the frequency-domain dielectric spectrum of the oil-impregnated paper inside the transformer without knowing the insulation structure parameters.

[0049] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in a transformer, characterized in that, It includes the following steps: S1: Measure the complex capacitance C of the main insulation of the transformer all * (ω), and calculate the frequency-domain dielectric spectrum ε all * (ω); S2: Measure the complex capacitance C of the insulating oil oil * (ω), and calculate the frequency-domain dielectric spectrum ε oil * (ω); S3: Calculate the frequency-domain dielectric spectrum ε all * (ω) of the main insulation and the frequency-domain dielectric spectrum ε oil * (ω) of the insulating oil, and calculate the frequency-domain dielectric spectrum ε paper * (ω) of the oil-impregnated paper under different insulation structure parameters; S4: The oil-immersed paper spectrum ε calculated under different insulation structures using the dielectric spectrum model paper * (ω) is fitted, and the group with the smallest fitting residual is the desired frequency domain dielectric spectrum of the oil-immersed paper; Specifically, S3 includes the following steps: S31: Calculate the frequency-domain dielectric spectrum ε of oil-impregnated paper according to the following formula paper * (ω): Where X is the ratio of the total thickness of each layer of oil-impregnated paper in the main insulation to the distance of the main insulation, and Y is the ratio of the total width of the spacers at each place to the average circumference of the high- and low-voltage windings. The initial values of X and Y are both 0.

1. S32: Gradually change the values of the insulation structure parameters X and Y, and calculate ε(ω) under different structure parameters. The value range of X is 0.1 - 0.5, the value range of Y is 0.1 - 0.3, and the step size is 0.01 for both. paper * (ω), the value range of X is 0.1 - 0.5, the value range of Y is 0.1 - 0.3, and the step size is 0.01 for both. The dielectric spectroscopy model in S4 is as follows: The fitting residual λ is defined as: Among them, ε' 拟合 and ε' 计算 are the real parts of the complex permittivity obtained by fitting and calculating using the dielectric spectroscopy model, respectively, and ε” 拟合 and ε” 计算 are the imaginary parts of the complex permittivity obtained by fitting and calculating using the dielectric spectroscopy model, respectively.

2. The method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in a transformer according to claim 1, characterized in that, The complex capacitance C in S1 and S2 all * (ω) and C oil * (ω) are directly measured by an impedance spectrometer, the frequency measurement range is 1 mHz - 10 kHz, and the frequency-domain dielectric spectrum ε * (ω) is calculated according to the following formula: where ω is the angular frequency, C * (ω) is the complex capacitance of the main insulation of the transformer or the insulating oil, and C0 is the geometric capacitance of the insulation.

3. The method for obtaining the frequency-domain dielectric spectrum of oil-impregnated paper in a transformer according to claim 1, wherein The basis for selecting the group with the smallest fitting residual in S4 as the solution result is as follows: The true frequency-domain dielectric spectrum ε paper * (ω) satisfies the dielectric spectrum model described by Equation (2), and its corresponding fitting residual is very small; while ε paper * (ω) calculated using incorrect structural parameter values X and Y has a large difference from the true value and cannot be accurately described by Equation (2), and its corresponding fitting residual is also large. Therefore, the group with the smallest fitting residual is the true ε paper * (ω).

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