Method for evaluating non-uniform wetting state of oil-immersed high-voltage bushing

Abstract

The application discloses an evaluation method for uneven moisture state of oil-immersed high-voltage bushing, and belongs to the technical field of power transformer operation and maintenance, which comprises the following steps: constructing a database of complex dielectric constant of oil-immersed paper insulation sample not affected by moisture; obtaining an expression of complex dielectric constant of oil-immersed paper under the influence of moisture content through a composite model of oil-water-paper complex dielectric constant; dividing the capacitor core under uneven moisture into a right upper region, a right lower region, a left upper region and a left lower region according to a moisture degree boundary line and a central axis of the capacitor core to study the moisture condition, constructing an equivalent capacitance model of the oil-immersed high-voltage bushing under uneven moisture, and thereby constructing a loss factor curve library of the capacitor core under uneven moisture; and according to moisture state parameters corresponding to a curve with the highest fitting degree in the loss factor curve library, accurately evaluating the uneven moisture degree of internal insulation of the oil-immersed bushing.

Description

Technical Field

[0001] This invention belongs to the field of power transformer operation and maintenance technology, and in particular relates to an assessment method for uneven moisture absorption of oil-immersed high-voltage bushings. Background Technology

[0002] Bushings are a crucial component of high-voltage oil-immersed power transformers, and their reliability directly impacts the transformer's stable operation. Based on bushing type, high-voltage bushings can be mainly divided into two categories: oil-paper insulated bushings and adhesive-paper insulated bushings, with oil-paper insulated bushings accounting for 70% of the total. Operational data statistics reveal that internal insulation defects, moisture absorption, aging, and overheating issues in oil-paper insulated bushings are the primary causes of transformer outages.

[0003] Based on on-site operation and maintenance experience, after long-term operation, bushings, due to their multi-layer equal-capacitance structure design and the limitation of limited and non-circulating insulating oil, tend to accumulate moisture at the bottom of the transformer inside the bushing due to its high moisture density. This results in a non-uniform moisture distribution at the bottom of most bushing insulation, with a clearly defined boundary between different moisture levels. This phenomenon was observed during the disassembly and analysis of some faulty bushings. Furthermore, because bushings are installed at a certain angle, the moisture content differs between the two sides of the bottom insulation of the core along the axial direction. Operational experience shows that the insulation condition of locally damp areas in the actual bushing capacitor core seriously threatens the safety and stability of the bushing. Traditional single-mode power frequency dielectric loss testing neglects the insulation condition of the lower, locally damp areas due to the influence of the well-insulated upper part of the bushing, thus failing to accurately quantify the moisture status of these localized areas.

[0004] Therefore, there is an urgent need for a new technical solution to address this problem. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for evaluating the uneven moisture state of oil-immersed high-pressure bushings, which solves the problem of not being able to accurately obtain the moisture state of unevenly moistened bushings.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for evaluating the uneven moisture state of an oil-immersed high-pressure bushing, comprising the following steps:

[0007] Step 1: Establish multiple oil-impregnated paper insulation samples simulating the internal insulation state of an oil-impregnated bushing under laboratory conditions;

[0008] Step 2: Aging treatment of oil-impregnated paper insulation samples to obtain oil-impregnated paper insulation samples with different aging degrees; test the complex dielectric constant of oil-impregnated paper insulation samples with different aging degrees at different temperatures, and construct a database of complex dielectric constants of oil-impregnated paper insulation samples that are not affected by moisture.

[0009] Step 3: Establish a composite model of the complex permittivity of oil-water-paper; obtain the expression for the complex permittivity of oil-impregnated paper under the influence of moisture content;

[0010] Step 4: Construct a theoretical model of an oil-immersed capacitive core structure with uneven moisture absorption; the theoretical model of the oil-immersed capacitive core structure with uneven moisture absorption is divided into upper and lower parts, with the moisture content of the upper region being lower than that of the lower region; the capacitor core is divided into upper right region, lower right region, upper left region, and lower left region by the moisture degree boundary line and the central axis of the capacitor core; based on the complex dielectric constant of the oil-immersed paper obtained in Step 3 under the influence of moisture content, construct an equivalent capacitance model of the capacitor core under uneven moisture absorption;

[0011] Step 5: Combine the complex dielectric constant database of oil-impregnated paper insulation samples established in Step 2, which is unaffected by moisture, with the composite model in Step 3; select an iteration range of 0.1% to 1% for moisture content and an iteration step size of 0.1% to establish the first complex dielectric constant database of oil-impregnated paper; select an iteration range of 1% to 7% for moisture content and an iteration step size of 0.1% to establish the second complex dielectric constant database of oil-impregnated paper.

[0012] Step Six: Substitute the first and second oil-impregnated paper complex dielectric constant databases established in Step Five into the equivalent capacitance model established in Step Four to calculate the equivalent complex capacitance of the capacitor core; the data from the first oil-impregnated paper complex dielectric constant database is used as the complex dielectric constant data for the upper region; the data from the second oil-impregnated paper complex dielectric constant database is used as the complex dielectric constant data for the lower region; extract the imaginary and real parts of the equivalent complex capacitance of the capacitor core, and calculate the loss factor of the capacitor core; set the zero-screen moisture distance h on the right side of the capacitor core. m The iteration range and iteration step size are determined to construct a library of loss factor curves for capacitor cores.

[0013] Step 7: Perform dielectric loss factor test on the high-voltage bushing of the oil-immersed power transformer on site to obtain its loss factor frequency domain curve and the on-site test temperature.

[0014] Step 8: Calculate the goodness of fit between the measured curve from Step 7 and each curve in the loss factor curve library from Step 6 at the field test temperature, and select the curve with the highest goodness of fit from the loss factor curve library; obtain the degree of aging of the oil-impregnated paper, the moisture content of the upper region of the capacitor core, the moisture content of the lower region, and the distance h of the zero screen on the right side of the capacitor core corresponding to this curve. m The value.

[0015] The preferred composite model of the complex permittivity of oil-water-paper in step three includes a first composite model, a second composite model, and a third composite model; the first composite model is:

[0016]

[0017] The second composite model is:

[0018]

[0019] The third composite model is:

[0020]

[0021] Where X1 and Y1, X2 and Y2, and X3 and Y3 are the scaling factors in the first composite model, the second composite model, and the third composite model, respectively, and ρ p The density of oil-impregnated paper, in grams per cubic centimeter (ρ). o The density of transformer oil, in grams per cubic centimeter (ρ). w υ is the density of water, in grams per cubic centimeter; M is the oil absorption rate of the insulating paper; and M is the moisture content of the oil-impregnated paper.

[0022] The expression for the complex permittivity of oil-impregnated paper under the influence of moisture content, as described in step three, is as follows:

[0023]

[0024] Where: ε r * (ω,M,T) represents the complex permittivity of the oil-impregnated paper under the influence of moisture content, ε p * (ω,M,T) is the complex permittivity of the oil-impregnated paper, unaffected by moisture, ε w * (ω,M,T) is the complex permittivity of water, ε o * (ω, M, T) represents the complex permittivity of the transformer oil, ω is the angular frequency of the test power supply (radians / second), T is the temperature (Kelvin), M is the moisture content in the oil-impregnated paper, and k1 and k2 are the mixing coefficients of the composite model. Based on the composite model of the complex permittivity, the basic data at different moisture contents are substituted into the equations, and the system of equations is solved to obtain k1 and k2. The expression is then derived through curve fitting.

[0025] k1=21.09218-21.09226×0.96237 M

[0026] k2=27.63244-38.17369×0.83627 M

[0027] Through the above design scheme, the present invention can bring the following beneficial effects:

[0028] 1. A composite model of the complex permittivity of oil-water-paper was established; the expression of the complex permittivity of oil-impregnated paper under the influence of moisture content was comprehensively considered; the universality of the model was enhanced.

[0029] 2. Divide the capacitor core under uneven moisture into upper right, lower right, upper left, and lower left regions based on the moisture degree boundary and the central axis of the capacitor core to study the moisture condition. Construct an equivalent capacitance model of the oil-immersed high-voltage bushing under uneven moisture condition to achieve an accurate assessment of the uneven moisture degree of the internal insulation of the oil-immersed bushing. Attached Figure Description

[0030] Figure 1 This is a flowchart of a method for evaluating the uneven moisture state of an oil-immersed high-pressure bushing according to the present invention.

[0031] Figure 2 This is a first composite model diagram of oil-water-paper for an evaluation method of uneven moisture state of an oil-immersed high-pressure bushing according to the present invention.

[0032] Figure 3 This is a second composite model diagram of oil-water-paper for an evaluation method of uneven moisture state of an oil-immersed high-pressure bushing according to the present invention.

[0033] Figure 4 This is a diagram of the third composite model of oil-water-paper for evaluating the uneven moisture state of an oil-immersed high-pressure bushing according to the present invention.

[0034] Figure 5 This is a theoretical model diagram of the capacitor core structure for an evaluation method of uneven moisture absorption in an oil-immersed high-voltage bushing according to the present invention.

[0035] Figure 6 This is an example of an evaluation method for uneven moisture absorption of an oil-immersed high-voltage bushing according to the present invention, showing the measurement and calculation curves of the loss factor of a 220 kV oil-immersed high-voltage bushing.

[0036] In the diagram: 1 - Upper left area of ​​capacitor core; 2 - Lower left area of ​​capacitor core; 3 - Sleeve tilt angle; 4 - Lower right area of ​​capacitor core; 5 - Upper right area of ​​capacitor core; 6 - Distance between left-side zero screen of capacitor core; 7 - Distance between capacitor screens; 8 - Length of capacitor screen; 9 - Radius of capacitor screen; 10 - Complementary angles of sleeve tilt angle; 11 - Distance between right-side zero screen of capacitor core; 12 - Length of lower step of capacitor core. Detailed Implementation

[0037] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0038] It should be noted that the terms "front and back," "up and down," and "left and right" mentioned in the text are merely simplified descriptions of positional relationships based on the accompanying drawings, and are not intended to limit the technical solution.

[0039] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive, and users may make various changes to the following parameters without departing from the inventive mechanism and scope set forth in the claims. To avoid obscuring the essence of the invention, well-known methods and processes are not described in detail.

[0040] From the appendix Figures 1-6 As shown: A method for assessing the uneven moisture condition of an oil-immersed high-pressure bushing, comprising the following steps:

[0041] Step 1: Establish multiple oil-impregnated paper insulation samples simulating the internal insulation state of an oil-impregnated bushing under laboratory conditions;

[0042] Step 2: Aging treatment of oil-impregnated paper insulation samples to obtain oil-impregnated paper insulation samples with different aging degrees; test the complex dielectric constant of oil-impregnated paper insulation samples with different aging degrees at different temperatures, and construct a database of complex dielectric constants of oil-impregnated paper insulation samples that are not affected by moisture.

[0043] Step 3: Establish a composite model of the complex permittivity of oil-water-paper; obtain the expression for the complex permittivity of oil-impregnated paper under the influence of moisture content;

[0044] Step 4: Construct a theoretical model of an oil-immersed capacitive core structure with uneven moisture absorption; the theoretical model of the oil-immersed capacitive core structure with uneven moisture absorption is divided into upper and lower parts, with the moisture content of the upper region being lower than that of the lower region; the capacitor core is divided into upper right region, lower right region, upper left region, and lower left region by the moisture degree boundary line and the central axis of the capacitor core; based on the complex dielectric constant of the oil-immersed paper obtained in Step 3 under the influence of moisture content, construct an equivalent capacitance model of the capacitor core under uneven moisture absorption;

[0045] Step 5: Combine the complex dielectric constant database of oil-impregnated paper insulation samples established in Step 2, which is unaffected by moisture, with the composite model in Step 3; select an iteration range of 0.1% to 1% for moisture content and an iteration step size of 0.1% to establish the first complex dielectric constant database of oil-impregnated paper; select an iteration range of 1% to 7% for moisture content and an iteration step size of 0.1% to establish the second complex dielectric constant database of oil-impregnated paper.

[0046] Step Six: Substitute the first and second oil-impregnated paper complex dielectric constant databases established in Step Five into the equivalent capacitance model established in Step Four to calculate the equivalent complex capacitance of the capacitor core; the data from the first oil-impregnated paper complex dielectric constant database is used as the complex dielectric constant data for the upper region; the data from the second oil-impregnated paper complex dielectric constant database is used as the complex dielectric constant data for the lower region; extract the imaginary and real parts of the equivalent complex capacitance of the capacitor core, and calculate the loss factor of the capacitor core; set the zero-screen moisture distance h on the right side of the capacitor core. m The iteration range and iteration step size are determined to construct a library of loss factor curves for capacitor cores.

[0047] The loss factor of the capacitor core is calculated as follows:

[0048]

[0049] Where: tanδ represents the loss factor of the capacitor core, C"(ω,M,T) represents the imaginary part of the equivalent complex capacitance of the capacitor core, C'(ω,M,T) represents the real part of the equivalent complex capacitance of the capacitor core, ω is the angular frequency of the test power supply in radians per second, T is the temperature in Kelvin, and M is the moisture content of the oil-impregnated paper.

[0050] Step 7: Perform dielectric loss factor test on the high-voltage bushing of the oil-immersed power transformer on site to obtain its loss factor frequency domain curve and the on-site test temperature.

[0051] Step 8: Calculate the goodness of fit between the measured curve from Step 7 and each curve in the loss factor curve library from Step 6 at the field test temperature, and select the curve with the highest goodness of fit from the loss factor curve library; obtain the degree of aging of the oil-impregnated paper, the moisture content of the upper region of the capacitor core, the moisture content of the lower region, and the distance h of the zero screen on the right side of the capacitor core corresponding to this curve. m The value.

[0052] The further step three describes a composite model for the complex permittivity of the oil-water-paper system, which includes a first composite model, a second composite model, and a third composite model, such as... Figures 2-4 As shown; the first composite model is:

[0053]

[0054] The second composite model is:

[0055]

[0056] The third composite model is:

[0057]

[0058] Where X1 and Y1, X2 and Y2, and X3 and Y3 are the scaling factors in the first composite model, the second composite model, and the third composite model, respectively, and ρ p The density of oil-impregnated paper, in grams per cubic centimeter (ρ). o The density of transformer oil, in grams per cubic centimeter (ρ). w υ is the density of water, in grams per cubic centimeter; M is the oil absorption rate of the insulating paper; and M is the moisture content of the oil-impregnated paper.

[0059] The expression for the complex permittivity of oil-impregnated paper under the influence of moisture content, as described in step three, is as follows:

[0060]

[0061] Where: ε r * (ω,M,T) represents the complex permittivity of the oil-impregnated paper under the influence of moisture content, ε p * (ω,M,T) is the complex permittivity of the oil-impregnated paper, unaffected by moisture, ε w * (ω,M,T) is the complex permittivity of water, ε o * (ω, M, T) represents the complex permittivity of the transformer oil, ω is the angular frequency of the test power supply (radians / second), T is the temperature (Kelvin), M is the moisture content in the oil-impregnated paper, and k1 and k2 are the mixing coefficients of the composite model. Based on the composite model of the complex permittivity, the basic data at different moisture contents are substituted into the equations, and the system of equations is solved to obtain k1 and k2. The expression is then derived through curve fitting.

[0062] k1=21.09218-21.09226×0.96237 M

[0063] k2=27.63244-38.17369×0.83627 M

[0064] Further step four describes dividing the capacitor core under uneven moisture conditions into upper right, lower right, upper left, and lower left regions using the moisture level boundary and the central axis of the capacitor core; the expression for constructing the equivalent capacitance model of the capacitor core under uneven moisture conditions is as follows:

[0065]

[0066] C *(ω,M,T) represents the equivalent complex capacitance of the capacitor core, ω represents the angular frequency of the test power supply in radians per second, T represents the temperature in Kelvin, M represents the moisture content in the oil-impregnated paper, d1 represents the denominator of the equivalent complex capacitance of the upper right region of the capacitor core, d2 represents the denominator of the equivalent complex capacitance of the lower right region of the capacitor core, d3 represents the denominator of the equivalent complex capacitance of the upper left region of the capacitor core, and d4 represents the denominator of the equivalent complex capacitance of the lower left region of the capacitor core.

[0067] When the moisture level boundary line passes through all capacitive screens, calculate the equivalent complex capacitance of the upper right region, lower right region, upper left region, and lower left region of the capacitor core respectively;

[0068] The equivalent complex capacitance of the upper right region of the capacitor core is

[0069]

[0070]

[0071] Where: C ru * (ω,M,T) represents the equivalent complex capacitance of the upper right region of the capacitor core, ε r1 * (ω, M, T) represents the complex permittivity of the oil-impregnated paper in the upper region of the capacitor core, and ε0 is the vacuum permittivity, ε0 ​​= 8.854 × 10⁻⁶. -12 Fab / meter, ω is the angular frequency of the test power supply (radians / second), T is the temperature (Kelvin), M is the moisture content of the oil-impregnated paper, π is pi (π≈3.14159), j is the number of segments in a single layer of insulation of the capacitor core, q is the total number of segments, and the value range of j is (0, q), h m The distance from the right side of the capacitor core to the zero screen where moisture has accumulated, in millimeters, λ. d R is the step length of the capacitor core, in millimeters (mm). i is the number of layers in the capacitor screen, and n is the total number of capacitor screens. The value of i ranges from (1, n). i r is the radius of the i-th layer of capacitive touchscreen, in millimeters. i-1 The radius of the (i-1)th layer of capacitive touchscreen, in millimeters, l i Let d1 be the length of the i-th layer of the capacitive touchscreen, in millimeters, and θ be the complementary angle of the sleeve tilt angle α. For ease of subsequent calculations, let d1 be C. ru * The denominator of (ω,M,T)

[0072] The equivalent complex capacitance of the lower right region of the capacitor core is:

[0073]

[0074]

[0075] Where: C rd * (ω,M,T) represents the equivalent complex capacitance of the lower right region of the capacitor core, ε r2 * (ω,M,T) represents the complex permittivity of the oil-impregnated paper in the lower region of the capacitor core. For ease of subsequent calculations, d2 is taken as C. rd * The denominator of (ω,M,T)

[0076] The equivalent complex capacitance of the upper left region of the capacitor core is

[0077]

[0078]

[0079] Where: C lu * (ω,M,T) represents the equivalent complex capacitance of the upper left region of the capacitor core, ε r1 * (ω,M,T) represents the complex permittivity of the oil-impregnated paper in the upper region of the capacitor core. For ease of subsequent calculations, d3 is taken as C. lu * The denominator of (ω,M,T), h l The distance from the left side of the capacitor core to the zero screen where moisture has accumulated, in millimeters, is expressed as follows:

[0080] h l =h m +2r0 tanθ

[0081] Where: r0 is the zero-screen radius of the capacitor core, in millimeters, h m The distance from the right side of the capacitor core to the zero screen where moisture is absorbed is measured in millimeters. θ is the complementary angle to the bushing tilt angle α.

[0082] The equivalent complex capacitance of the lower left region of the capacitor core is:

[0083]

[0084]

[0085] Where: C ld * (ω,M,T) represents the equivalent complex capacitance of the lower left region of the capacitor core, ε r2 * (ω,M,T) represents the complex permittivity of the oil-impregnated paper in the lower region of the capacitor core. For ease of subsequent calculations, d4 is taken as C. ld * The denominator of (ω,M,T)

[0086] When the moisture level boundary does not pass through all capacitive screens, consider the area on the right side of the capacitor core starting from the a-th screen, where h appears. m -(a-1)λ d -(r a -r a-1 In the case where tanθ≤0,

[0087] The equivalent complex capacitance model for the upper right region of the capacitor core is as follows:

[0088]

[0089] Where: C ru * (ω,M,T) represents the equivalent complex capacitance of the upper right region of the capacitor core, ε r1 * (ω,M,T) represents the complex permittivity of the oil-impregnated paper in the upper region of the capacitor core, a is the initial number of the single-layer capacitor screen on the right side completely located in the upper region of the capacitor core, i is the number of capacitor screen layers, n is the total number of capacitor screens, and the value of i ranges from (1,n). d1 is C ru * The denominator of (ω,M,T)

[0090] The equivalent complex capacitance of the lower right region of the capacitor core is:

[0091]

[0092]

[0093] Where: C rd * (ω,M,T) represents the equivalent complex capacitance of the lower right region of the capacitor core, ε r2 * (ω,M,T) represents the complex permittivity of the oil-impregnated paper in the lower region of the capacitor core, a is the initial layer number of the single-layer capacitor screen on the right that is completely located in the upper region of the capacitor core, and i ranges from (1,a-1). For ease of subsequent calculations, d2 is taken as C. rd * The denominator of (ω,M,T)

[0094] When the moisture level boundary does not pass through all capacitive screens, consider starting from the left side of the capacitor core, beginning with the b-th layer of screen, where h appears. l -(b-1)λ d +(r b -r b-1 In the case where tanθ≤0,

[0095] The equivalent complex capacitance model for the upper left region of the capacitor core is as follows:

[0096]

[0097] Where: C lu * (ω,M,T) represents the equivalent complex capacitance of the upper left region of the capacitor core, ε r1 * (ω,M,T) represents the complex permittivity of the oil-impregnated paper in the upper region of the capacitor core, i is the number of layers of the capacitor screen, n is the total number of capacitor screens, and the value of i ranges from (1,n). b is the starting layer number where the single-layer capacitor screen on the left is completely located in the upper region of the capacitor core. For ease of subsequent calculations, d3 is taken as C. lu * The denominator of (ω,M,T)

[0098] Equivalent complex capacitance in the lower left region of the capacitor core

[0099]

[0100]

[0101] Where: C ld * (ω,M,T) represents the equivalent complex capacitance of the lower left region of the capacitor core, ε r2 * (ω,M,T) represents the complex permittivity of the oil-impregnated paper in the lower region of the capacitor core, and the value of i ranges from (1,b-1). For ease of subsequent calculations, d4 is taken as C. ld * The denominator of (ω,M,T).

[0102] Further step six describes the moisture distance h of the right-side zero screen. m The iteration range is (λ d ,l1 / 2+λ d The iteration step size is λ. d ,

[0103] Where: λ d l1 is the length of the lower step of the capacitor core, in millimeters; l1 is the length of the first layer of the capacitor screen, in millimeters.

[0104] The formula for calculating the goodness of fit in further step eight is as follows:

[0105]

[0106] Where: J represents the goodness of fit between the calculated curve and the measured curve, and its value range is (0,1). The closer J is to 1, the better the goodness of fit. p is the extracted loss points, p = 1~3 represents 3 points extracted in the low frequency band, p = 4~6 represents 3 points extracted in the mid frequency band, p = 7~9 represents 3 points extracted in the high frequency band, and z 1p To calculate the loss factor value of the curve, z 2p This represents the loss factor value of the measured curve.

[0107] In practice, multiple oil-impregnated paper insulation samples established under laboratory conditions were aged to obtain oil-impregnated paper insulation samples with different aging degrees. Different temperatures were selected: 10℃, 20℃, 40℃, 60℃, 80℃, and 100℃. Different aging degrees were selected: 0 days, 10 days, 20 days, 40 days, and 55 days of aging. The constructed database of the dielectric constant of oil-impregnated paper was substituted into the equivalent capacitance model, and the moisture-receiving distance h on the right side of the capacitor core was set. m The initial iteration value is 9 mm, the final iteration value is 1980 mm, the iteration step size is 9 mm, and the moisture content in the upper region of the capacitor core is less than that in the lower region. The number of capacitor screens in the capacitor core is 57.

[0108] The dielectric loss factor curve of a 220 kV oil-paper capacitor bushing was measured at an on-site test temperature of 26℃. The measured curve is shown below. Figure 6 As shown.

[0109] The extracted frequencies in the low-frequency band are 0.0022 Hz, 0.046 Hz, and 0.22 Hz; the extracted frequencies in the mid-frequency band are 4.6 Hz, 40 Hz, and 70 Hz; and the extracted frequencies in the high-frequency band are 220 Hz, 470 Hz, and 1000 Hz. Using the method of this invention, the highest fitting degree J between the calculated curve and the measured curve is 0.9613. The calculated curve corresponds to a moisture content of 0.6% in the upper region of the capacitor core and a degree of polymerization of 695 for the oil-impregnated paper. The moisture content in the lower region of the capacitor core is 1.8%, and the degree of polymerization of the oil-impregnated paper is also 695. The distance h from the zero-screen moisture absorption point on the right side of the capacitor core is also considered. m The value is 873 mm, and the calculated curve is as follows: Figure 6 As shown.

[0110] Obviously, the embodiments described above are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for evaluating the uneven moisture absorption state of an oil-immersed high-pressure bushing, characterized in that, Includes the following steps: Step 1: Establish multiple oil-impregnated paper insulation samples simulating the internal insulation state of an oil-impregnated bushing under laboratory conditions; Step 2: Aging treatment of oil-impregnated paper insulation samples to obtain oil-impregnated paper insulation samples with different aging degrees; test the complex dielectric constant of oil-impregnated paper insulation samples with different aging degrees at different temperatures, and construct a database of complex dielectric constants of oil-impregnated paper insulation samples that are not affected by moisture. Step 3: Establish a composite model of the complex permittivity of oil-water-paper; the composite model of the complex permittivity of oil-water-paper includes a first composite model, a second composite model, and a third composite model; the first composite model is: The second composite model is: The third composite model is: in, X 1 and Y 1. X 2 and Y 2. X 3 and Y 3 represents the proportionality coefficients in the first, second, and third composite models, respectively. ρ p This refers to the density of oil-impregnated paper, in grams per cubic centimeter. ρ o This refers to the density of transformer oil, in grams per cubic centimeter. ρ w The density of water, in grams per cubic centimeter. υ This refers to the oil absorption rate of the insulating paper. M This refers to the moisture content within the oil-impregnated paper. The complex dielectric constant expression of oil-impregnated paper under the influence of moisture content was obtained; Step 4: Construct a theoretical model of an oil-immersed capacitive core structure with uneven moisture absorption; the theoretical model of the oil-immersed capacitive core structure with uneven moisture absorption is divided into upper and lower parts, with the moisture content of the upper region being lower than that of the lower region; the capacitor core is divided into upper right region, lower right region, upper left region, and lower left region by the moisture degree boundary line and the central axis of the capacitor core; based on the complex dielectric constant of the oil-immersed paper obtained in Step 3 under the influence of moisture content, construct an equivalent capacitance model of the capacitor core under uneven moisture absorption; Step 5: Combine the complex dielectric constant database of oil-impregnated paper insulation samples established in Step 2, which is unaffected by moisture, with the composite model in Step 3; select an iteration range of 0.1% to 1% for moisture content and an iteration step size of 0.1% to establish the first complex dielectric constant database of oil-impregnated paper; select an iteration range of 1% to 7% for moisture content and an iteration step size of 0.1% to establish the second complex dielectric constant database of oil-impregnated paper. Step Six: Substitute the first and second oil-impregnated paper complex dielectric constant databases established in Step Five into the equivalent capacitance model established in Step Four to calculate the equivalent complex capacitance of the capacitor core; the data from the first oil-impregnated paper complex dielectric constant database is used as the complex dielectric constant data for the upper region; the data from the second oil-impregnated paper complex dielectric constant database is used as the complex dielectric constant data for the lower region; extract the imaginary and real parts of the equivalent complex capacitance of the capacitor core, and calculate the loss factor of the capacitor core; set the zero-screen moisture distance on the right side of the capacitor core. The iteration range and iteration step size are determined to construct a library of loss factor curves for capacitor cores. Step 7: Perform dielectric loss factor test on the high-voltage bushing of the oil-immersed power transformer on site to obtain its loss factor frequency domain curve and the on-site test temperature. Step 8: Calculate the goodness of fit between the measured curve from Step 7 and each curve in the loss factor curve library from Step 6 at the field test temperature. Select the curve in the loss factor curve library with the highest goodness of fit to the measured curve. Obtain the corresponding oil-impregnated paper aging degree, moisture content in the upper region of the capacitor core, moisture content in the lower region, and the distance to the zero screen on the right side of the capacitor core. The value.

2. The method for evaluating the uneven moisture state of an oil-immersed high-pressure bushing according to claim 1, characterized in that, The expression for the complex permittivity of oil-impregnated paper under the influence of moisture content, as described in step three, is as follows: in: ε r * ( ω , M , T ( ) represents the complex dielectric constant of oil-impregnated paper under the influence of moisture content. ε p * ( ω , M , T ( ) represents the complex permittivity of oil-impregnated paper, which is unaffected by moisture. ε w * ( ω , M , T Let be the complex permittivity of water. ε o * ( ω , M , T Let be the complex permittivity of the transformer oil. ω To test the angular frequency of the power supply, the unit is radians per second. T Temperature, unit: Kelvin M This refers to the moisture content within the oil-impregnated paper. k 1. k 2 represents the mixing coefficient of the composite model; .

3. The method for evaluating the uneven moisture state of an oil-immersed high-pressure bushing according to claim 1, characterized in that, The expression for constructing the equivalent capacitance model of the capacitor core under uneven moisture conditions, as described in step four, is as follows: C * ( ω , M , T ) is the equivalent complex capacitance of the capacitor core. ω To test the angular frequency of the power supply, the unit is radians per second. T Temperature, unit: Kelvin M This refers to the moisture content within the oil-impregnated paper. d 1 is the denominator of the equivalent complex capacitance of the upper right region of the capacitor core. d 2 is the denominator of the equivalent complex capacitance of the lower right region of the capacitor core. d 3 is the denominator of the equivalent complex capacitance of the upper left region of the capacitor core. d 4 is the denominator of the equivalent complex capacitance of the lower left region of the capacitor core; When the moisture level boundary line passes through all capacitive screens, calculate the equivalent complex capacitance of the upper right region, lower right region, upper left region, and lower left region of the capacitor core respectively; The equivalent complex capacitance of the upper right region of the capacitor core is in: C ru * ( ω , M , T The symbol ) represents the equivalent complex capacitance of the upper right region of the capacitor core. ε r1 * ( ω , M , T () represents the complex permittivity of the oil-impregnated paper in the upper region of the capacitor core. ε 0 is the vacuum permittivity. ε 0 = 8.854 × 10 -12 Fab / meter, ω To test the angular frequency of the power supply, the unit is radians per second. T Temperature, unit: Kelvin M The value represents the moisture content of the oil-impregnated paper, and π represents pi (π ≈ 3.14159). j This refers to the number of segments in the single layer of insulation of the capacitor core. q This represents the total number of segments. j The range of values ​​for is (0, q ), h m The distance from the right side of the capacitor core to the zero screen where moisture has accumulated, in millimeters. λ d The lower step length of the capacitor core, in millimeters. i This refers to the number of layers in the capacitive touchscreen. n This represents the total number of capacitive touchscreens. i The range of values ​​for is (1, ...). n ), r i For the first i The radius of a capacitive touchscreen, in millimeters. r i-1 For the first i -1 layer capacitive touchscreen radius, unit: millimeters. l i For the first i Length of the capacitive touchscreen, in millimeters. θ The casing tilt angle α The complementary angles are taken as follows for ease of subsequent calculations. d 1 is C ru * ( ω , M , T The denominator of the fraction is... The equivalent complex capacitance of the lower right region of the capacitor core is: in: C rd * ( ω , M , T The symbol ) represents the equivalent complex capacitance in the lower right region of the capacitor core. ε r2 * ( ω , M , T Let represent the complex permittivity of the oil-impregnated paper in the lower region of the capacitor core. For ease of subsequent calculations, let be . d 2 is C rd * ( ω , M , T The denominator of the fraction is... The equivalent complex capacitance of the upper left region of the capacitor core is in: C lu * ( ω , M , T The symbol represents the equivalent complex capacitance of the upper left region of the capacitor core. ε r1 * ( ω , M , T Let represent the complex permittivity of the oil-impregnated paper in the upper region of the capacitor core. For ease of subsequent calculations, let be . d 3 is C lu * ( ω , M , T The denominator of the fraction is... h l The distance from the left side of the capacitor core to the zero screen where moisture has accumulated, in millimeters, is expressed as follows: in: r 0 represents the zero-radius of the capacitor core, in millimeters. h m The distance from the right side of the capacitor core to the zero screen where moisture has accumulated, in millimeters. θ The casing tilt angle α complementary angles, The equivalent complex capacitance of the lower left region of the capacitor core is: in: C ld * ( ω , M , T The symbol ) represents the equivalent complex capacitance in the lower left region of the capacitor core. ε r2 * ( ω , M , T Let represent the complex permittivity of the oil-impregnated paper in the lower region of the capacitor core. For ease of subsequent calculations, let be . d 4 C ld * ( ω , M , T The denominator of the fraction is... When the moisture level boundary does not pass through all capacitive screens, consider the right side region of the capacitor core from the first... a Layered screens begin to appear h m -( a -1) λ d -( r a - r a-1 )tan θ In the case of ≤0, The equivalent complex capacitance model for the upper right region of the capacitor core is as follows: in: C ru * ( ω , M , T The symbol ) represents the equivalent complex capacitance of the upper right region of the capacitor core. ε r1 * ( ω , M , T () represents the complex permittivity of the oil-impregnated paper in the upper region of the capacitor core. a This refers to the starting layer number where the single-layer capacitive screen on the right is completely located in the upper region of the capacitor core. i This refers to the number of layers in the capacitive touchscreen. n This represents the total number of capacitive touchscreens. i The range of values ​​for is (1, ...). n ), d 1 is C ru * ( ω , M , T The denominator of the fraction is... The equivalent complex capacitance of the lower right region of the capacitor core is: in: C rd * ( ω , M , T The symbol ) represents the equivalent complex capacitance in the lower right region of the capacitor core. ε r2 * ( ω , M , T () represents the complex permittivity of the oil-impregnated paper in the lower region of the capacitor core. a This refers to the starting layer number where the single-layer capacitive screen on the right is completely located in the upper region of the capacitor core. i The range of values ​​for is (1, ...). a -1), for ease of subsequent calculations, take d 2 is C rd * ( ω , M , T The denominator of the fraction is... When the moisture level boundary does not pass through all capacitive screens, consider starting from the left side of the capacitor core, beginning with the... b Layered screens begin to appear h l -( b -1) λ d +( r b - r b-1 )tan θ In the case of ≤0, The equivalent complex capacitance model for the upper left region of the capacitor core is as follows: in: C lu * ( ω , M , T The symbol represents the equivalent complex capacitance of the upper left region of the capacitor core. ε r1 * ( ω , M , T () represents the complex permittivity of the oil-impregnated paper in the upper region of the capacitor core. i This refers to the number of layers in the capacitive touchscreen. n This represents the total number of capacitive touchscreens. i The range of values ​​for is (1, ...). n ), b Let be the starting layer number where the single-layer capacitive screen on the left is completely located in the upper region of the capacitor core. For ease of subsequent calculations, let be... d 3 is C lu * ( ω , M , T The denominator of the fraction is... Equivalent complex capacitance in the lower left region of the capacitor core in: C ld * ( ω , M , T The symbol ) represents the equivalent complex capacitance in the lower left region of the capacitor core. ε r2 * ( ω , M , T () represents the complex permittivity of the oil-impregnated paper in the lower region of the capacitor core. i The range of values ​​for is (1, ...). b -1), for ease of subsequent calculations, take d 4 C ld * ( ω , M , T The denominator of ).

4. The method for evaluating the uneven moisture state of an oil-immersed high-pressure bushing according to claim 1, characterized in that, Step six describes the moisture distance of the right-side zero screen. h m The iteration range is ( λ d , l 1 / 2+ λ d The iteration step size is λ d , in: λ d The lower step length of the capacitor core, in millimeters. The length of the first layer of capacitive touchscreen, in millimeters.

5. The method for evaluating the uneven moisture state of an oil-immersed high-pressure bushing according to claim 1, characterized in that, The formula for calculating the goodness of fit in step eight is as follows: in: J This represents the goodness of fit between the calculated curve and the measured curve, and its value range is (0,1). J The closer a value is to 1, the higher the degree of fit. p The extracted loss points, p =1~3 represents 3 points extracted in the low-frequency band. p =4~6 represents 3 points extracted in the mid-frequency band. p =7~9 indicates 3 points extracted from the high-frequency band. z 1p To calculate the loss factor value of the curve, z 2p This represents the loss factor value of the measured curve.

6. The method for evaluating the uneven moisture state of an oil-immersed high-pressure bushing according to claim 5, characterized in that, The extracted frequencies for the low-frequency band are 0.0022 Hz, 0.046 Hz, and 0.22 Hz; the extracted frequencies for the mid-frequency band are 4.6 Hz, 40 Hz, and 70 Hz; and the extracted frequencies for the high-frequency band are 220 Hz, 470 Hz, and 1000 Hz.

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