Method for evaluating the degree of electric field distortion of an oil-immersed high-voltage bushing

Abstract

The application discloses an evaluation method for oil-immersed high-voltage bushing electric field distortion degree, and belongs to the technical field of power transformer evaluation, which comprises the following steps: constructing a resistivity database of oil-immersed paper insulation samples; dividing the capacitor core under uneven damp into a right upper area, a right lower area, a left upper area and a left lower area according to the damp degree boundary line and the central axis of the capacitor core to study the damp condition; constructing an equivalent resistance model of the oil-immersed high-voltage bushing under uneven damp; calculating the equivalent resistance between each capacitor screen of the high-voltage bushing of the oil-immersed power transformer in the field according to the moisture content of the upper and lower areas of the oil-immersed high-voltage bushing and the right side zero screen damp distance corresponding to the curve with the highest curve fitting degree in the measured curve and the loss factor curve library, so as to obtain the electric field intensity borne by the insulation between each capacitor screen, and realize the quantitative and accurate evaluation of the electric field distribution of the local area in the oil-immersed bushing.

Description

Technical Field

[0001] This invention belongs to the field of power transformer evaluation technology, and in particular relates to a method for evaluating the degree of electric field distortion in oil-immersed high-voltage bushings. Background Technology

[0002] The reliability of bushings directly affects the stable operation of transformers. Oil-paper insulated bushings account for 70% of the total number of high-voltage bushings. Under complex operating conditions, since the insulating oil inside the bushing has no external cooling system, the internal insulation of the bushing will be subjected to more severe combined effects of electricity and heat. At the same time, the generation of bubbles after the bushing insulation becomes damp or the accelerated aging of the insulation will cause stress concentration in the electric field inside the bushing, resulting in partial discharge inside the bushing. Insulation defects, dampness, aging, and overheating problems inside oil-paper insulated bushings are the main causes of transformer shutdown accidents.

[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 bushing due to its high water density. This results in a non-uniform moisture distribution at the bottom of most bushings, with a clear boundary between different moisture levels. This phenomenon was observed during the disassembly and analysis of some faulty bushings. Furthermore, because the 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. The actual localized moisture state of the insulation directly determines the local electric field distribution characteristics of the bushing during operation. In severe cases, this can lead to localized electric field concentration, seriously threatening the safety and stability of the bushing. Traditional single-mode power frequency dielectric loss testing neglects the insulation state of the lower, locally moistened areas due to the influence of the well-insulated upper part of the bushing, and also fails to consider the effect of the tilt angle. Therefore, it is impossible to accurately quantify the electric field distribution in localized areas of the bushing.

[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 degree of electric field distortion in oil-immersed high-voltage bushings, which solves the problem of not being able to accurately quantify the electric field distribution in local areas of the bushing.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for evaluating the degree of electric field distortion in an oil-immersed high-voltage bushing, comprising the following steps:

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

[0008] Step 2: Perform resistivity tests on oil-impregnated paper insulation samples at different temperatures and moisture contents, and construct a resistivity database accordingly;

[0009] Step 3: Construct a theoretical model of the unevenly damped oil-immersed sleeve capacitor core structure; the theoretical model of the unevenly damped oil-immersed sleeve capacitor core structure 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; construct an equivalent resistance model between each capacitor screen under uneven moisture conditions;

[0010] Step 4: 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.

[0011] Step 5: Establish a composite model of oil-water-paper; obtain the complex dielectric constant expression of oil-impregnated paper under the influence of moisture content;

[0012] Step 6: Based on the theoretical model of the unevenly damp oil-immersed bushing capacitor core structure constructed in Step 3 and the complex dielectric constant of the oil-immersed paper under the influence of moisture content obtained in Step 5, construct the equivalent capacitance model of the capacitor core under uneven dampness.

[0013] Step 7: Combine the complex dielectric constant database of oil-impregnated paper insulation samples established in Step 4, which is unaffected by moisture, with the composite model in Step 5; 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.

[0014] Step 8: Substitute the first and second oil-impregnated paper complex dielectric constant databases established in Step 7 into the equivalent capacitance model established in Step 6 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.

[0015] Step 9: 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.

[0016] Step 10: Calculate the goodness of fit between the measured curve from Step 9 and each curve in the loss factor curve library from Step 8 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 moisture content of the upper region, the moisture content of the lower region, and the moisture-receiving distance h of the right side of the capacitor core of the oil-immersed bushing capacitor corresponding to this curve. m The value;

[0017] Step 11: Combine the moisture content of the upper and lower regions of the capacitor core obtained in Step 10 with the on-site test temperature and the resistivity database from Step 2 to obtain the equivalent insulation resistivity between the capacitor screens in the upper right, lower right, upper left, and lower left regions of the capacitor core; combine the equivalent insulation resistivity between the capacitor screens in the upper right, lower right, upper left, and lower left regions of the capacitor core with the moisture distance h of the zero screen on the right side of the capacitor core obtained in Step 10. m The values ​​are substituted into the equivalent resistance model of the capacitor core under uneven moisture in step three to calculate the equivalent resistance between each capacitor panel of the high-voltage bushing of the oil-immersed power transformer on site.

[0018] Step 12: Based on the equivalent resistance between each capacitor screen obtained in Step 11, use the electric field strength calculation model to obtain the electric field strength borne by the insulation between each capacitor screen of the capacitor core, and determine whether the electric field is distorted and the degree of electric field distortion; the electric field strength calculation model is as follows:

[0019]

[0020] Where: E i R is the electric field strength borne by the insulation between the capacitor plates of the capacitor core, U is the applied voltage on the capacitor core, and R is the electric field strength. i Let r be the equivalent resistance between the capacitor plates of the capacitor core, i be the number of capacitor plate layers, and r be the equivalent resistance between the capacitor plates. i Let r be the radius of the i-th layer of capacitive touchscreen. i-1 Let be the radius of the (i-1)th layer of capacitive touchscreen.

[0021] Through the above design scheme, the present invention can bring the following beneficial effects:

[0022] The capacitor core under uneven moisture is divided into upper right, lower right, upper left, and lower left regions by the moisture degree boundary line and the central axis of the capacitor core. The moisture condition is studied, and an equivalent resistance model of the oil-immersed high-voltage bushing under uneven moisture is constructed to realize the quantitative and accurate assessment of the electric field distribution in the local area inside the oil-immersed bushing. Attached Figure Description

[0023] Figure 1This is a flowchart of a method for evaluating the degree of electric field distortion in an oil-immersed high-voltage bushing according to the present invention.

[0024] Figure 2 This is a first composite model diagram of oil-water-paper for the method of evaluating the degree of electric field distortion of an oil-immersed high-voltage bushing according to the present invention.

[0025] Figure 3 This is a second composite model diagram of oil-water-paper for the method of evaluating the degree of electric field distortion of an oil-immersed high-voltage bushing according to the present invention.

[0026] Figure 4 This is a diagram of the third composite model of oil-water-paper for the method of evaluating the degree of electric field distortion of an oil-immersed high-voltage bushing according to the present invention.

[0027] Figure 5 This is a theoretical model diagram of the capacitor core structure for the method of evaluating the degree of electric field distortion of an oil-immersed high-voltage bushing according to the present invention.

[0028] Figure 6 This is an example of an embodiment of the method for evaluating the degree of electric field distortion of an oil-immersed high-voltage bushing according to the present invention, showing the measurement curve and calculation curve of the loss factor of a 220 kV oil-immersed high-voltage bushing.

[0029] Figure 7 This is a diagram showing the electric field distribution inside the capacitor core in an embodiment of the method for evaluating the degree of electric field distortion in an oil-immersed high-voltage bushing according to the present invention.

[0030] 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

[0031] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] 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.

[0033] 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.

[0034] From the appendix Figures 1-7 As shown: A method for evaluating the degree of electric field distortion in an oil-immersed high-voltage bushing includes the following steps:

[0035] Step 1: Establish multiple oil-impregnated paper insulation samples under laboratory conditions; the oil-impregnated paper insulation samples are oil-impregnated paper insulation samples that simulate the internal insulation state of an oil-impregnated bushing.

[0036] Step 2: Perform resistivity tests on oil-impregnated paper insulation samples at different temperatures and moisture contents, and construct a resistivity database accordingly;

[0037] Step 3: Construct a theoretical model of the unevenly damped oil-immersed sleeve capacitor core structure; the theoretical model of the unevenly damped oil-immersed sleeve capacitor core structure 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; construct an equivalent resistance model between each capacitor screen under uneven moisture conditions;

[0038] Step 4: 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.

[0039] Step 5: Establish a composite model of oil-water-paper; obtain the complex dielectric constant expression of oil-impregnated paper under the influence of moisture content;

[0040] Step 6: Based on the theoretical model of the unevenly damp oil-immersed bushing capacitor core structure constructed in Step 3 and the complex dielectric constant of the oil-immersed paper under the influence of moisture content obtained in Step 5, construct the equivalent capacitance model of the capacitor core under uneven dampness.

[0041] Step 7: Combine the complex dielectric constant database of oil-impregnated paper insulation samples established in Step 4, which is unaffected by moisture, with the composite model in Step 5; 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.

[0042] Step 8: Substitute the first and second oil-impregnated paper complex dielectric constant databases established in Step 7 into the equivalent capacitance model established in Step 6 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.

[0043] Step 9: 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.

[0044] Step 10: Calculate the goodness of fit between the measured curve from Step 9 and each curve in the loss factor curve library from Step 8 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 moisture content of the upper region, the moisture content of the lower region, and the moisture-receiving distance h of the right side of the capacitor core of the oil-immersed bushing capacitor corresponding to this curve. m The value;

[0045] Step 11: Combine the moisture content of the upper and lower regions of the capacitor core obtained in Step 10 with the on-site test temperature and the resistivity database from Step 2 to obtain the equivalent insulation resistivity between the capacitor screens in the upper right, lower right, upper left, and lower left regions of the capacitor core; combine the equivalent insulation resistivity between the capacitor screens in the upper right, lower right, upper left, and lower left regions of the capacitor core with the moisture distance h of the zero screen on the right side of the capacitor core obtained in Step 10. m The values ​​are substituted into the equivalent resistance model of the capacitor core under uneven moisture in step three to calculate the equivalent resistance between each capacitor panel of the high-voltage bushing of the oil-immersed power transformer on site.

[0046] Step 12: Based on the equivalent resistance between each capacitor screen obtained in Step 11, use the electric field strength calculation model to obtain the electric field strength borne by the insulation between each capacitor screen of the capacitor core, and determine whether the electric field is distorted and the degree of electric field distortion; the electric field strength calculation model is as follows:

[0047]

[0048] Among them: E i R is the electric field strength borne by the insulation between the capacitor plates of the capacitor core, U is the applied voltage on the capacitor core, and R is the electric field strength. iLet r be the equivalent resistance between the capacitor plates of the capacitor core, i be the number of capacitor plate layers, and r be the equivalent resistance between the capacitor plates. i Let r be the radius of the i-th layer of capacitive touchscreen. i-1 Let be the radius of the (i-1)th layer of capacitive touchscreen.

[0049] The equivalent resistance model between the capacitor screens in step three, where the capacitor core is subjected to uneven moisture, is as follows:

[0050]

[0051] Where: R i ρ is the equivalent resistance between the capacitor plates of the capacitor core. rui ρ represents the equivalent insulation resistivity between the capacitor plates in the upper right region of the capacitor core. lui ρ represents the equivalent insulation resistivity between the capacitor plates in the upper left region of the capacitor core. rdi ρ represents the equivalent insulation resistivity between the capacitor plates in the lower right region of the capacitor core. ldi This represents the equivalent insulation resistivity between the capacitor screens in the lower left region of the capacitor core, where i is the number of capacitor screen layers, q is the total number of segments in a single layer of insulation of the capacitor core, and e1 is the equivalent resistance R between the capacitor screens in the upper right region of the capacitor core. rui The denominator, e2, represents the equivalent resistance R between the capacitor screens in the lower right region of the capacitor core. rdi The denominator, e3, represents the equivalent resistance R between the capacitor screens in the upper left region of the capacitor core. lui The denominator, e4, represents the equivalent resistance R between the capacitor screens in the lower left region of the capacitor core. ldi The denominator;

[0052] When the moisture level boundary line passes through all the capacitor screens, calculate the equivalent resistance between the capacitor screens in the upper right region, lower right region, upper left region, and lower left region of the capacitor core, respectively.

[0053] The equivalent resistance between the capacitor and the capacitor screen in the upper right area of ​​the capacitor core is

[0054]

[0055]

[0056] Where: R rui The value of j represents the equivalent resistance between the capacitor screens in the upper right region of the capacitor core, 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). m The distance from the right side of the capacitor core to the zero screen where moisture has accumulated, in millimeters. π is pi, approximately 3.14159. λ d R is the step length of the capacitor core, in millimeters; i is the number of layers in the capacitor screen; n is the total number of capacitor screens; the value of i ranges from (1, n); ri r is the radius of the i-th layer of capacitive touchscreen, in millimeters. i-1 Let e1 be the radius of the (i-1)th layer of the capacitor screen, and θ be the complementary angle of the sleeve tilt angle α. For ease of subsequent calculations, let e1 be R. rui The denominator, l i Let be the length of the i-th layer of capacitive touchscreen.

[0057] l i =l1-(i-1)(λ d +λ u )

[0058] λ u l1 is the length of the upper step, and l1 is the length of the first layer of capacitive screen.

[0059] ρ rui The equivalent insulation resistivity between the capacitor screens in the upper right region of the capacitor core is expressed as follows:

[0060]

[0061] Where: ρ rui ρ represents the equivalent insulation resistivity between the capacitor screens in the upper right region of the capacitor core. u (M,T) represents the resistivity of the upper region of the capacitor core, where M is the moisture content of the oil-impregnated paper, T represents the temperature inside the capacitor core (unit: Kelvin), r represents the radial direction of the capacitor core, and y represents the axial direction of the capacitor core.

[0062] The equivalent resistance between the capacitor and the screen in the lower right area of ​​the capacitor core is:

[0063]

[0064]

[0065] Where: R rdi This represents the equivalent resistance between the capacitor plates in the lower right region of the capacitor core. For ease of subsequent calculations, e2 is taken as R. rdi The denominator, ρ rdi The equivalent insulation resistivity between the capacitor screen and the lower right side region of the capacitor core is expressed as follows:

[0066]

[0067] Where: ρ rdi ρ represents the equivalent insulation resistivity between the capacitor screens in the lower right region of the capacitor core. d (M,T) represents the resistivity value of the lower region of the capacitor core.

[0068] The equivalent resistance between the capacitor screen and the left upper region of the capacitor core is:

[0069]

[0070]

[0071] Where: R lui h represents the equivalent resistance between the capacitor plates in the upper left region of the capacitor core. 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:

[0072] h l =h m +2r0tanθ

[0073] Where: r0 is the zero-screen radius of the capacitor core, in millimeters. For ease of subsequent calculations, e3 is taken as R. lui The denominator, ρ lui The equivalent insulation resistivity between the capacitor screen and the left upper region of the capacitor core is expressed as follows:

[0074]

[0075] Where: ρ lui ρ represents the equivalent interlayer insulation resistivity of the upper left region of the capacitor core. u (M,T) represents the resistivity value of the upper region of the capacitor core.

[0076] The equivalent resistance between the capacitor plates in the lower left area of ​​the capacitor core is:

[0077]

[0078]

[0079] Where: R ldi This represents the equivalent resistance between the capacitor plates in the lower left region of the capacitor core. For ease of subsequent calculations, e4 is taken as R. ldi The denominator, ρ ldi The equivalent insulation resistivity between the capacitor plates in the lower left region of the capacitor core is expressed as follows:

[0080]

[0081] Where: ρ ldi ρd(M,T) represents the equivalent insulation resistivity between the capacitor screen and the lower left side of the capacitor core, where ρd(M,T) represents the resistivity value of the lower region of the capacitor core.

[0082] When the moisture level boundary line does not pass through all capacitive touchscreens, starting from the a-th layer of capacitive touchscreens, all subsequent capacitive touchscreens are located in the upper region of the capacitor core, that is, the right side region of the capacitor core begins to show h from the a-th layer of touchscreens. m -(a-1)λ d -(r a-r a-1 When tanθ≤0, the equivalent resistance between the capacitor plates in the upper right region of the capacitor core is:

[0083]

[0084]

[0085] Where 'a' represents the initial layer number where the right-side single-layer capacitive screen is completely located in the upper region of the capacitor core, and ρ rui The equivalent insulation resistivity between the capacitor screens in the upper right region of the capacitor core is expressed as follows:

[0086]

[0087] The expression for the equivalent resistance between the capacitor screens in the lower right region of the capacitor core is the same as the expression for the moisture level boundary line when it passes through all the capacitor screens. However, only the equivalent resistance between the first a-1 layers of capacitor screens is calculated. Starting from the a-th layer of capacitor screens, the equivalent resistance between the capacitor screens is calculated based on the equivalent resistance between the capacitor screens in the upper region of the capacitor core.

[0088] When the moisture level boundary line does not pass through all capacitive screens, that is, when the left side region of the capacitor core starts to show h from the b-th screen layer... l -(b-1)λ d -(r b -r b-1 When tanθ≤0, the equivalent resistance between the capacitor plates in the upper left region of the capacitor core is:

[0089]

[0090]

[0091] ρ lui The equivalent insulation resistivity between the capacitor screen and the left upper region of the capacitor core is expressed as follows:

[0092]

[0093] Where b is the starting layer number of the single-layer capacitive screen on the left side, which is completely located in the upper region of the capacitive core.

[0094] The equivalent resistance expression between the capacitor screens in the lower left region of the capacitor core is the same as the moisture level boundary line when it passes through all the capacitor screens, but only the equivalent resistance between the first b-1 layers of capacitor screens is calculated. Starting from the b-th layer of capacitor screens, the equivalent resistance between the capacitor screens is calculated according to the equivalent resistance between the capacitor screens in the upper region of the capacitor core.

[0095] The further step five 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 2-4As shown; the first composite model is:

[0096]

[0097] The second composite model is:

[0098]

[0099] The third composite model is:

[0100]

[0101] 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.

[0102] The expression for the complex permittivity of oil-impregnated paper under the influence of moisture content, as described in step five, is as follows:

[0103]

[0104] 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.

[0105] k1=21.09218-21.09226×0.96237 M

[0106] k2=27.63244-38.17369×0.83627 M .

[0107] The further step, step six, describes the expression for constructing the equivalent capacitance model of the capacitor core under uneven moisture conditions:

[0108]

[0109] 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.

[0110] 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;

[0111] The equivalent complex capacitance of the upper right region of the capacitor core is

[0112]

[0113]

[0114] 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)

[0115] The equivalent complex capacitance of the lower right region of the capacitor core is:

[0116]

[0117]

[0118] 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)

[0119] The equivalent complex capacitance of the upper left region of the capacitor core is

[0120]

[0121]

[0122] 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:

[0123] h l =h m +2r0tanθ

[0124] 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.

[0125] The equivalent complex capacitance of the lower left region of the capacitor core is:

[0126]

[0127]

[0128] 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)

[0129] 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,

[0130] The equivalent complex capacitance model for the upper right region of the capacitor core is as follows:

[0131]

[0132]

[0133] 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)

[0134] The equivalent complex capacitance of the lower right region of the capacitor core is:

[0135]

[0136]

[0137] 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)

[0138] 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,

[0139] The equivalent complex capacitance model for the upper left region of the capacitor core is as follows:

[0140]

[0141]

[0142] 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)

[0143] Equivalent complex capacitance in the lower left region of the capacitor core

[0144]

[0145]

[0146] 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).

[0147] Further step eight 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 ,

[0148] 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.

[0149] The formula for calculating the goodness of fit in further step ten is as follows:

[0150]

[0151] 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.

[0152] 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: -40℃, -30℃, -20℃, -10℃, 0℃, 10℃, 30℃, 50℃, 70℃, 90℃, and 100℃. Different moisture contents were also selected: 0.2%, 1.5%, 2.7%, 3.2%, 4.4%, 5.1%, 6.3%, and 7.1%. The resistivity database for different moisture contents was expanded using the gradient descent method to further obtain the resistivity of oil-impregnated paper at arbitrary moisture contents.

[0153] Different aging levels were selected as 0 days, 10 days, 20 days, 40 days, and 55 days of aging, with the zero-screen moisture distance h set on the right side of the capacitor core. m The initial iteration value was 9 mm, the final iteration value was 1980 mm, the iteration step size was 9 mm, and the moisture content in the upper region of the capacitor core was guaranteed to be less than that in the lower region. The number of capacitor screens inside the capacitor core was 57. The dielectric loss factor curve of a 220 kV oil-paper capacitor bushing was measured. The on-site test temperature was 26℃, and the measured curve is shown below. Figure 6 As shown.

[0154] The extracted frequency points for the low-frequency band are 0.0022 Hz, 0.046 Hz, and 0.22 Hz; the extracted frequency points for the mid-frequency band are 4.6 Hz, 40 Hz, and 70 Hz; and the extracted frequency points for 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, 1.8% in the lower region, and a moisture absorption distance h on the right side of the capacitor core. m The value is 873 mm, and the calculated curve is as follows: Figure 6 As shown.

[0155] Substituting the moisture content of the upper region of the capacitor core (0.6%), the moisture content of the lower region (1.8%), and the on-site test temperature (26℃) into the resistivity database in step two, the resistivity ρ of the upper region of the capacitor core is obtained. u (M,T) is 1.65×10 12 Ω / m, resistivity ρ of the lower region d (M,T) is 2.77 × 10 11 Ω / m; The complementary angle θ of the high-voltage bushing tilt angle of the field oil-immersed power transformer is 10 degrees, the total number of segments q is set to 30, and the lower step length λ of the capacitor core is... d It is 9mm; the upper step length λ u The length is 22 mm, and the length l1 of the first layer of capacitive screen is 3251 mm. Iterative calculation is used to determine whether h appears in the right region of the capacitor core starting from the a-th layer of screen. m -(a-1)λ d -(r a -r a-1 In the case where tanθ≤0, a is calculated to be 57, meaning the moisture boundary line does not completely pass through the 57th screen layer in the right region; iterative calculation is used to determine whether h appears in the left region of the capacitor core starting from the bth screen layer. l -(b-1)λ d -(r b -r b-1 When tanθ≤0, b is calculated to be 57, meaning the moisture boundary line does not completely pass through the 57th screen in the left region; therefore, the equivalent resistance and equivalent insulation resistance between the capacitor screens in the upper right region of the capacitor core are .

[0156]

[0157]

[0158]

[0159] The equivalent resistance and equivalent insulation resistance between the capacitor plates in the upper left area of ​​the capacitor core are _____.

[0160]

[0161]

[0162]

[0163] The equivalent resistance and equivalent insulation resistance of the capacitor core in the lower right region between the capacitor screens are 100%.

[0164]

[0165]

[0166]

[0167] The equivalent resistance and equivalent insulation resistance between the capacitor plates in the lower left area of ​​the capacitor core are 100%.

[0168]

[0169]

[0170] The resistivity ρ of the upper region of the capacitor core u (M,T) and resistivity ρ of the lower region d (M,T) and the distance h of the zero screen moisture on the right side of the capacitor core obtained in step ten. m Substituting the 873 mm, the equivalent resistance between the capacitor screens in the above-mentioned regions, and the equivalent insulation resistivity into the equivalent resistance model of the capacitor core under uneven moisture in step three, the equivalent resistance between each capacitor screen of the high-voltage bushing of the field oil-immersed power transformer is calculated; the electric field strength borne by the insulation between each capacitor screen of the capacitor core is obtained using the electric field strength calculation model.

[0171] The degree of electric field distortion can be assessed based on the electric field distribution curve, such as... Figure 7 As shown, the electric field within the capacitor core is distorted at the 57th layer of the capacitor screen, i.e., the last screen, where the electric field strength is 42.25 kV / mm. This causes a flashover discharge, which breaks down the bushing.

[0172] 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 degree of electric field distortion in an oil-immersed high-voltage bushing, characterized in that, Includes the following steps: Step 1: Establish multiple oil-impregnated paper insulation samples under laboratory conditions; the oil-impregnated paper insulation samples are oil-impregnated paper insulation samples that simulate the internal insulation state of an oil-impregnated bushing. Step 2: Perform resistivity tests on oil-impregnated paper insulation samples at different temperatures and moisture contents, and construct a resistivity database accordingly; Step 3: Construct a theoretical model of the unevenly damped oil-immersed sleeve capacitor core structure; the theoretical model of the unevenly damped oil-immersed sleeve capacitor core structure 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; construct an equivalent resistance model between each capacitor screen under uneven moisture conditions; Step 4: 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 5: Establish a composite model of oil-water-paper; obtain the complex dielectric constant expression of oil-impregnated paper under the influence of moisture content; Step 6: Based on the theoretical model of the unevenly damp oil-immersed bushing capacitor core structure constructed in Step 3 and the complex dielectric constant of the oil-immersed paper under the influence of moisture content obtained in Step 5, construct the equivalent capacitance model of the capacitor core under uneven dampness. Step 7: Combine the complex dielectric constant database of oil-impregnated paper insulation samples established in Step 4, which is unaffected by moisture, with the composite model in Step 5; 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 8: Substitute the first and second oil-impregnated paper complex dielectric constant databases established in Step 7 into the equivalent capacitance model established in Step 6 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. Step 9: 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 10: Calculate the goodness of fit between the measured curve from Step 9 and each curve in the loss factor curve library from Step 8 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 moisture content of the upper region, the moisture content of the lower region, and the moisture-receiving distance h of the right side of the capacitor core of the oil-immersed bushing capacitor corresponding to this curve. m The value; Step 11: Combine the moisture content of the upper and lower regions of the capacitor core obtained in Step 10 with the on-site test temperature and the resistivity database from Step 2 to obtain the equivalent insulation resistivity between the capacitor screens in the upper right, lower right, upper left, and lower left regions of the capacitor core; combine the equivalent insulation resistivity between the capacitor screens in the upper right, lower right, upper left, and lower left regions of the capacitor core with the moisture distance h of the zero screen on the right side of the capacitor core obtained in Step 10. m The values ​​are substituted into the equivalent resistance model of the capacitor core under uneven moisture in step three to calculate the equivalent resistance between each capacitor panel of the high-voltage bushing of the oil-immersed power transformer on site. Step 12: Based on the equivalent resistance between each capacitor screen obtained in Step 11, use the electric field strength calculation model to obtain the electric field strength borne by the insulation between each capacitor screen of the capacitor core, and determine whether the electric field is distorted and the degree of electric field distortion. The electric field strength calculation model is as follows: Among them: E i R is the electric field strength borne by the insulation between the capacitor plates of the capacitor core, U is the applied voltage on the capacitor core, and R is the electric field strength. i Let r be the equivalent resistance between the capacitor plates of the capacitor core, i be the number of capacitor plate layers, and r be the equivalent resistance between the capacitor plates. i Let r be the radius of the i-th layer of capacitive touchscreen. i-1 Let be the radius of the (i-1)th layer of capacitive touchscreen.

2. The method for evaluating the degree of electric field distortion in an oil-immersed high-voltage bushing according to claim 1, characterized in that, The equivalent resistance model between the capacitor screens under uneven moisture conditions, as described in step three, is as follows: Where: R i ρ is the equivalent resistance between the capacitor plates of the capacitor core. rui ρ represents the equivalent insulation resistivity between the capacitor plates in the upper right region of the capacitor core. lui ρ represents the equivalent insulation resistivity between the capacitor plates in the upper left region of the capacitor core. rdi ρ represents the equivalent insulation resistivity between the capacitor plates in the lower right region of the capacitor core. ldi This represents the equivalent insulation resistivity between the capacitor screens in the lower left region of the capacitor core, where i is the number of capacitor screen layers, q is the total number of segments in a single layer of insulation of the capacitor core, and e1 is the equivalent resistance R between the capacitor screens in the upper right region of the capacitor core. rui The denominator, e2, represents the equivalent resistance R between the capacitor screens in the lower right region of the capacitor core. rdi The denominator, e3, represents the equivalent resistance R between the capacitor screens in the upper left region of the capacitor core. lui The denominator, e4, represents the equivalent resistance R between the capacitor screens in the lower left region of the capacitor core. ldi The denominator; When the moisture level boundary line passes through all the capacitor screens, calculate the equivalent resistance between the capacitor screens in the upper right region, lower right region, upper left region, and lower left region of the capacitor core, respectively. The equivalent resistance between the capacitor and the capacitor screen in the upper right area of ​​the capacitor core is Where: R rui The value of j represents the equivalent resistance between the capacitor screens in the upper right region of the capacitor core, 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). m The distance from the right side of the capacitor core to the zero screen where moisture has accumulated, in millimeters. π is pi, approximately 3.14159. λ d R is the step length of the capacitor core, in millimeters; i is the number of layers in the capacitor screen; n is the total number of capacitor screens; the value of i ranges from (1, n); r 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 e1 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 e1 be R. rui The denominator, ρ rui The equivalent insulation resistivity between the capacitor screens in the upper right region of the capacitor core is expressed as follows: Where: ρ rui ρ represents the equivalent insulation resistivity between the capacitor screens in the upper right region of the capacitor core. u (M,T) represents the resistivity of the upper region of the capacitor core, where M is the moisture content of the oil-impregnated paper, T represents the temperature inside the capacitor core (unit: Kelvin), r represents the radial direction of the capacitor core, and y represents the axial direction of the capacitor core. The equivalent resistance between the capacitor and the screen in the lower right area of ​​the capacitor core is: Where: R rdi This represents the equivalent resistance between the capacitor plates in the lower right region of the capacitor core. For ease of subsequent calculations, e2 is taken as R. rdi The denominator, ρ rdi The equivalent insulation resistivity between the capacitor screen and the lower right side region of the capacitor core is expressed as follows: Where: ρ rdi ρ represents the equivalent insulation resistivity between the capacitor screens in the lower right region of the capacitor core. d (M,T) represents the resistivity value of the lower region of the capacitor core. The equivalent resistance between the capacitor screen and the left upper region of the capacitor core is: Where: R lui h represents the equivalent resistance between the capacitor plates in the upper left region of the capacitor core. 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: h l =h m +2r0 tanθ Where: r0 is the zero-screen radius of the capacitor core, in millimeters. For ease of subsequent calculations, e3 is taken as R. lui The denominator, ρ lui The equivalent insulation resistivity between the capacitor screen and the left upper region of the capacitor core is expressed as follows: Where: ρ lui ρ represents the equivalent interlayer insulation resistivity of the upper left region of the capacitor core. u (M,T) represents the resistivity value of the upper region of the capacitor core. The equivalent resistance between the capacitor plates in the lower left area of ​​the capacitor core is: Where: R ldi This represents the equivalent resistance between the capacitor plates in the lower left region of the capacitor core. For ease of subsequent calculations, e4 is taken as R. ldi The denominator, ρ ldi The equivalent insulation resistivity between the capacitor plates in the lower left region of the capacitor core is expressed as follows: Where: ρ ldi ρ represents the equivalent insulation resistivity between the capacitor screens in the lower left region of the capacitor core. d (M,T) represents the resistivity value of the lower region of the capacitor core. When the moisture level boundary line does not pass through all capacitive touchscreens, starting from the a-th layer of capacitive touchscreens, all subsequent capacitive touchscreens are located in the upper region of the capacitor core, that is, the right side region of the capacitor core begins to show h from the a-th layer of touchscreens. m -(a-1)λ d -(r a -r a-1 When tanθ≤0, the equivalent resistance between the capacitor plates in the upper right region of the capacitor core is: Where 'a' represents the initial layer number where the right-side single-layer capacitive screen is completely located in the upper region of the capacitor core, and ρ rui The equivalent insulation resistivity between the capacitor screen and the upper right side region of the capacitor core is expressed as follows: The expression for the equivalent resistance between the capacitor screens in the lower right region of the capacitor core is the same as the expression for the moisture level boundary line when it passes through all the capacitor screens. However, only the equivalent resistance between the first a-1 layers of capacitor screens is calculated. Starting from the a-th layer of capacitor screens, the equivalent resistance between the capacitor screens is calculated based on the equivalent resistance between the capacitor screens in the upper region of the capacitor core. When the moisture level boundary line does not pass through all the capacitive screens, that is, when the left side region of the capacitor core starts to show h from the b-th screen... l -(b-1)λ d -(r b -r b-1 When tanθ≤0, the equivalent resistance between the capacitor plates in the upper left region of the capacitor core is: ρ lui The equivalent insulation resistivity between the capacitor screen and the left upper region of the capacitor core is expressed as follows: Where b is the starting layer number of the single-layer capacitive screen on the left side, which is completely located in the upper region of the capacitive core. The equivalent resistance expression between the capacitor screens in the lower left region of the capacitor core is the same as the moisture level boundary line when it passes through all the capacitor screens, but only the equivalent resistance between the first b-1 layers of capacitor screens is calculated. Starting from the b-th layer of capacitor screens, the equivalent resistance between the capacitor screens is calculated according to the equivalent resistance between the capacitor screens in the upper region of the capacitor core.

3. The method for evaluating the degree of electric field distortion in an oil-immersed high-voltage bushing according to claim 1, characterized in that, The composite model of the complex permittivity of oil-water-paper described in step five 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: 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. The expression for the complex permittivity of oil-impregnated paper under the influence of moisture content, as described in step five, is as follows: 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 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, and k1 and k2 represent the mixing coefficients of the composite model. k1＝21.09218-21.09226×0.96237 M k2＝27.63244-38.17369×0.83627 M 。 4. The method for evaluating the degree of electric field distortion in an oil-immersed high-voltage 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 six, is as follows: 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. 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 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 Moisture-proof distance on the right side of the capacitor core, unit: 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) The equivalent complex capacitance of the lower right region of the capacitor core is: 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) The equivalent complex capacitance of the upper left region of the capacitor core is 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: h l =h m +2r0 tanθ 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 of the bushing tilt angle α. The equivalent complex capacitance of the lower left region of the capacitor core is: 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) 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, The equivalent complex capacitance model for the upper right region of the capacitor core is as follows: 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) The equivalent complex capacitance of the lower right region of the capacitor core is: 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) 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, The equivalent complex capacitance model for the upper left region of the capacitor core is as follows: 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) Equivalent complex capacitance in the lower left region of the capacitor core 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).

5. The method for evaluating the degree of electric field distortion in an oil-immersed high-voltage bushing according to claim 1, characterized in that, Step 8 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 , 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.

6. The method for evaluating the degree of electric field distortion in an oil-immersed high-voltage bushing according to claim 1, characterized in that, The formula for calculating the goodness of fit in step ten is as follows: 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.

7. The method for evaluating the degree of electric field distortion in an oil-immersed high-voltage bushing according to claim 6, 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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