An accurate evaluation method for oil-paper insulation aging degree based on time-domain dielectric spectroscopy

Abstract

The present invention provides an accurate evaluation method for the aging degree of oil-paper insulation based on time-domain dielectric spectrum. The present invention extends the number of branches of the extended Debye model to infinity, uses infinite relaxation polarization time to characterize the polarization process inside the medium, and constructs a corresponding distributed Debye model. On this basis, according to the concept of relaxation time distribution, dielectric relaxation sensitively depends on the composition, structure, bond type and other physical and chemical properties of the material, especially the multi-level structure and two-phase structure of the insulating paper cellulose itself and the two-phase structure of the interface between the two materials of oil and paper, which determines the complexity and multiplicity of relaxation polarization inside the oil-paper composite insulation. By analyzing the relationship between the probability density peak value and the aging degree in the distributed Debye model of oil-paper insulation samples with different aging degrees, an aging state evaluation model is established. Compared with the traditional dielectric response model, the accurate extraction of the dielectric relaxation process is achieved, and the evaluation accuracy of the aging state is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil-paper insulation equipment status diagnosis, and in particular to a method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy. Background Art

[0002] Transformer bushings are the core equipment for power transmission and transformation, and their safe and stable operation is of great significance to the stability of the power grid. Failure of large power transformers in operation may cause a major power outage, causing huge economic losses and negative impacts on society.

[0003] Oil-paper insulation is a common insulation type used in transformer bushings, and reliable insulation diagnosis has important social and economic significance. The polarization / depolarization current (PDC) analysis method based on dielectric response theory is a non-destructive and long-term dielectric response analysis method that can intuitively and effectively obtain polarization information closely related to the dielectric state, and has attracted widespread attention from researchers at home and abroad.

[0004] At present, there are two main approaches to using PDC data to analyze insulation aging status: one is to establish a database based on a large number of PDC curves of oil-paper insulation in different aging states obtained from laboratory and field experiments, and then fit and compare the measured results with the database through a certain data analysis method to obtain the insulation condition of the transformer under test; the other is to use dielectric-related theory to decompose the measured results through dielectric response functions and circuit models, extract characteristic parameters that characterize the insulation state, and use the characteristic parameters to characterize the insulation condition of the transformer under test.

[0005] The first method relies on a database and requires a large number of experimental results of different parameters. The more complete the database, the higher the accuracy of the judgment. It is the most widely used method at present, and there are many commercial instruments, such as the PDC insulation state analyzer produced by ALFF of Switzerland and the DIRANA dielectric response analyzer developed by Omicron of Austria. Since a large number of transformers have been replaced in China, there is a lack of data tracking for multiple transformers from the beginning of service to retirement. There are certain problems with the validity and representativeness of the data, which requires time accumulation and a huge workload.

[0006] The second method relies on a suitable and effective dielectric response function and an appropriate circuit model, as well as advanced data acquisition and analysis algorithms. By mining PDC data, it is possible to provide characteristic quantities that characterize the insulation state, making the judgment concise and clear, and more suitable for field applications. However, due to the limitations of theory, experiment, and data processing technology, the application of this method in the field of oil-paper insulation is still immature and requires further research.

[0007] The extended Debye model is a widely used circuit model in oil-paper insulation. The unique material composition and multi-level structure of the oil-paper insulation system and the complex operating conditions of the equipment determine the complexity and multiplicity of relaxation polarization inside the insulation. These characteristics are suitable for description using the distributed Debye model.

[0008] However, the representativeness of each branch in the extended Debye model for oil and paper is unclear, the determination of the number of branches is subjective, and there is a lack of objective criteria. For a medium with a certain state, when the number of branches reaches a certain number, increasing the number of branches has little effect on the fitting results, which makes different researchers obtain different circuit parameters for the same sample, thus limiting the further application of the model.

[0009] In order to solve the above problems, the present invention constructs a corresponding distributed Debye model, and solves the relaxation time distribution function of the oil-paper insulation medium response from the PDC depolarization current data. On this basis, the relationship between the probability density peak value in the relaxation time distribution function and the aging state of the oil-paper insulation is established, and the accurate evaluation of the aging state of the transformer bushing insulation is achieved. Summary of the invention

[0010] In view of this, the object of the present invention is to provide a method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy, so as to at least solve the above problems.

[0011] The technical solution adopted by the present invention is as follows:

[0012] A method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy, the method comprising the following steps:

[0013] S1. Construct a distributed Debye model based on dielectric relaxation theory and determine the relaxation time distribution function;

[0014] S2. Based on the idea of ​​solving a linear equation system, the PDC depolarization current is used to solve the dielectric relaxation time distribution function;

[0015] S3. For oil-paper insulation samples in different aging states, the relationship between the probability density peak in the relaxation time distribution function and the aging state of the oil-paper insulation is constructed to achieve accurate assessment of the aging degree.

[0016] Furthermore, in step S1, a distributed Debye model is constructed according to the dielectric relaxation theory, and the relaxation time distribution function is determined to be:

[0017] Polarization relaxation time τ is a characteristic time constant that marks the speed of the relaxation polarization process. The larger the τ value, the longer the relaxation polarization process takes to establish and dissipate, and vice versa. The relaxation time τ depends on the characteristics of the dielectric itself and is closely related to the external temperature. As the temperature increases, τ decreases sharply according to the exponential law, which can be expressed as:

[0018]

[0019] Where η0 is a constant; a is the dipole radius, m; W η is the activation energy of molecular viscous flow, kJ / mol;

[0020] For the relaxation process of defect dipole orientation polarization, the relaxation time τ depends on the properties of the crystal and its defects and the external temperature, and changes exponentially with temperature:

[0021]

[0022] Where, ν is the ion thermal vibration frequency, Hz; U is the ion activation energy, kJ / mol;

[0023] When the polarization is provided by multiple relaxation motions with similar relaxation times, P r (t) can be expressed as the relaxation time τ i Unequal polarization components P ri (t) Sum:

[0024]

[0025] In order to indicate that the relaxation time τ takes continuous values ​​in the range of 0 to ∞, the distribution function g(τ) is used to represent the distribution of τ. g(τ) is the probability density of the relaxation time distribution, and g(τ)dτ represents the probability that the relaxation time is in the range of τ to τ+dτ. From the probability point of view, the relaxation time distribution function is normalized, that is, g(τ) is:

[0026]

[0027] Further, in step S2, based on the idea of ​​solving a linear equation system, the PDC depolarization current is used to solve the dielectric relaxation time distribution function, which is specifically:

[0028] In order to determine the relationship between the relaxation time distribution function and the PDC depolarization current curve, a transformation is performed based on the idea of ​​solving a linear equation system:

[0029] PDC polarization current polarization current i p The relationship with the polarization time t is as follows:

[0030]

[0031] Among them U c is the charging voltage, C0 is the geometric capacitance of the sample, σ is the conductivity of the sample, ε0 is the vacuum dielectric constant, f(t) is the relaxation function of the sample, i p It consists of two parts: conduction current and polarization current;

[0032] The relationship between depolarization current id and discharge time t:

[0033] i d (t) = -C0U c [f(t)-f(t+T c )]

[0034] Where T c Represents the charging time, i d It does not contain conductive current, but is only generated by the depolarization process, which is the sum of the discharge currents of various polarization types inside the medium;

[0035] When the charging cycle is long enough, it can be known from the properties of the dielectric response function:

[0036] i d (t) = -C0U c [f(t)-f(t+T c )]=-C0U c f(t)

[0037] Thus there is

[0038] f(t)=-i d (t) / C0U c

[0039] The current is reversed

[0040] f(t)=i' d (t) / C0U c

[0041] At the same time, through the known relationship:

[0042] j(t)=dP r / dt=(ε s -ε ∞ )ε0E0f(t)

[0043] If there is only a single relaxation mechanism in the medium, according to the Debye theory:

[0044] f(t)=e (-t / τ) / τ

[0045] At this time, g(τ) is a delta function. If there are finite relaxation times in the medium, then g(τ) is

[0046] g1(τ)=delta(τ)

[0047] g2(τ)=ρ1delta(τ1)+ρ2delta(τ2)

[0048] ………

[0049] gn (τ)=ρ1delta(τ1)+ρ2delta(τ2)+…ρ n delta(τ n )

[0050] at this time,

[0051]

[0052] In the limit case, when the τ value is continuously distributed,

[0053]

[0054] By calculation

[0055]

[0056] Then the relationship between the measured PDC depolarization current and the required relaxation time distribution function g(τ) is simplified to:

[0057]

[0058] Since it is impossible to directly obtain the analytical expression of the relaxation time distribution function g(τ), the integral is discretized and its numerical solution is obtained. The current data before 1s is truncated, and τ is taken as 100 points in the logarithm of 1-Tc. The number of equation data points is based on the number obtained by actual measurement, which is set to m. An m×100 equation group with 100 variables is established, and the discretized equation group is as follows:

[0059]

[0060] The problem of solving the dielectric relaxation time distribution function using the PDC depolarization current is reduced to finding the numerical solution of the linear equation system A*x=b.

[0061] Furthermore, in step S3, for oil-paper insulation samples in different aging states, the relationship between the probability density peak value in the relaxation time distribution function and the aging state of the oil-paper insulation is constructed to achieve an accurate assessment of the aging degree:

[0062] The PDC curves of oil-paper insulation samples with different aging degrees were tested respectively, and the PDC data were converted into corresponding relaxation time distribution functions. The relationship between the probability density peak and the aging degree was constructed based on the least squares method. The transient and steady-state current characteristics of the tested samples were included in the PDC test results. For the oil-paper insulation samples, the polarization and depolarization times were both 1000s. Keithley 6517A and GPIB IEEE-488 were used to place the oil-paper insulation sample in a three-electrode structure for PDC testing. After a DC voltage U0 was applied to the tested sample, the maintenance time t pol, the current flowing through the medium is the polarization current i pol , remove the external voltage, short-circuit the sample under test, and maintain the time t depol , the current released in the medium is the depolarization current i depol According to the discrete equations, the relaxation time distribution function under the corresponding depolarization current is solved to obtain the aging state evaluation formula of oil-paper insulation:

[0063]

[0064] The accuracy of the evaluation was verified by using new oil-paper insulation samples, and the relative error index was used to measure its accuracy:

[0065]

[0066] Among them, DP is the calculated value of the evaluation model, DP 实测 It is the experimental test value.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] The present invention provides a method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy. Compared with the traditional dielectric response model, the present invention realizes the accurate extraction of the dielectric relaxation process and greatly improves the evaluation accuracy of the aging state.

[0069] The present invention utilizes the PDC depolarization current and realizes the solution of the medium relaxation time distribution function based on the idea of ​​solving a linear equation group.

[0070] The present invention establishes an index evaluation model for the aging state of oil-paper insulation by analyzing the relationship between the probability density peak value and the aging degree in a distributed Debye model. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only preferred embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0072] Figure 1 It is a schematic diagram of the overall process of a method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy provided by an embodiment of the present invention.

[0073] Figure 2 It is a schematic diagram of depolarization current curves of samples with different aging degrees according to a method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy provided by an embodiment of the present invention.

[0074] Figure 3 It is a schematic diagram of the relaxation time distribution function of samples with different aging degrees in a method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy provided by an embodiment of the present invention.

[0075] Figure 4 It is a schematic diagram of a curve showing the relationship between a probability density peak value and a sample polymerization degree of a method for accurately evaluating the degree of aging of oil-paper insulation based on time-domain dielectric spectroscopy provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0076] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The enumerated embodiments are only used to explain the present invention and are not used to limit the scope of the present invention.

[0077] Reference Figure 1 Figure 4 The present invention provides a method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy, the method comprising the following steps:

[0078] S1. Construct a distributed Debye model based on dielectric relaxation theory and determine the relaxation time distribution function;

[0079] S2. Based on the idea of ​​solving a linear equation system, the PDC depolarization current is used to solve the dielectric relaxation time distribution function;

[0080] S3. For oil-paper insulation samples in different aging states, the relationship between the probability density peak in the relaxation time distribution function and the aging state of the oil-paper insulation is constructed to achieve accurate assessment of the aging degree.

[0081] In step S1, a distributed Debye model is constructed according to the dielectric relaxation theory, and the relaxation time distribution function is determined as follows:

[0082] Polarization relaxation time τ is a characteristic time constant that marks the speed of the relaxation polarization process. The larger the τ value, the longer the relaxation polarization process takes to establish and dissipate, and vice versa. The relaxation time τ depends on the characteristics of the dielectric itself and is closely related to the external temperature. As the temperature increases, τ decreases sharply according to the exponential law, which can be expressed as:

[0083]

[0084] Where η0 is a constant; a is the dipole radius, m; W η is the activation energy of molecular viscous flow, kJ / mol;

[0085] For the relaxation process of defect dipole orientation polarization, the relaxation time τ depends on the properties of the crystal and its defects and the external temperature, and changes exponentially with temperature:

[0086]

[0087] Where, ν is the ion thermal vibration frequency, Hz; U is the ion activation energy, kJ / mol;

[0088] When the polarization is provided by multiple relaxation motions with similar relaxation times, P r (t) can be expressed as the relaxation time τ i Unequal polarization components P ri (t) Sum:

[0089]

[0090] In order to indicate that the relaxation time τ takes continuous values ​​in the range of 0 to ∞, the distribution function g(τ) is used to represent the distribution of τ. g(τ) is the probability density of the relaxation time distribution, and g(τ)dτ represents the probability that the relaxation time is in the range of τ to τ+dτ. From the probability point of view, the relaxation time distribution function is normalized, that is, g(τ) is:

[0091]

[0092] In step S2, based on the idea of ​​solving a linear equation system, the PDC depolarization current is used to solve the dielectric relaxation time distribution function, which is specifically:

[0093] In order to determine the relationship between the relaxation time distribution function and the PDC depolarization current curve, a transformation is performed based on the idea of ​​solving a linear equation system:

[0094] PDC polarization current polarization current i p The relationship with the polarization time t is as follows:

[0095]

[0096] Among them U c is the charging voltage, C0 is the geometric capacitance of the sample, σ is the conductivity of the sample, ε0 is the vacuum dielectric constant, f(t) is the relaxation function of the sample, i p It consists of two parts: conduction current and polarization current;

[0097] The relationship between depolarization current id and discharge time t:

[0098] i d (t) = -C0U c [f(t)-f(t+T c )]

[0099] Where T c Represents the charging time, i d It does not contain conductive current, but is only generated by the depolarization process, which is the sum of the discharge currents of various polarization types inside the medium;

[0100] When the charging cycle is long enough, it can be known from the properties of the dielectric response function:

[0101] i d (t) = -C0U c [f(t)-f(t+T c )]=-C0U c f(t)

[0102] Thus there is

[0103] f(t)=-i d (t) / C0U c

[0104] The current is reversed

[0105] f(t)=i' d (t) / C0U c

[0106] At the same time, through the known relationship:

[0107] j(t)=dP r / dt=(ε s -ε ∞ )ε0E0f(t)

[0108] If there is only a single relaxation mechanism in the medium, according to the Debye theory:

[0109] f(t)=e (-t / τ) / τ

[0110] At this time, g(τ) is a delta function. If there are finite relaxation times in the medium, then g(τ) is

[0111] g1(τ)=delta(τ)

[0112] g2(τ)=ρ1delta(τ1)+ρ2delta(τ2)

[0113] ………

[0114] g n (τ)=ρ1delta(τ1)+ρ2delta(τ2)+…ρ n delta(τ n )

[0115] at this time,

[0116]

[0117] In the limit case, when the τ value is continuously distributed,

[0118]

[0119] By calculation

[0120]

[0121] Then the relationship between the measured PDC depolarization current and the required relaxation time distribution function g(τ) is simplified to:

[0122]

[0123] Since it is impossible to directly obtain the analytical expression of the relaxation time distribution function g(τ), the integral is discretized and its numerical solution is obtained. The current data before 1s is truncated, and τ is taken as 100 points in the logarithm of 1-Tc. The number of equation data points is based on the number obtained by actual measurement, which is set to m. An m×100 equation group with 100 variables is established, and the discretized equation group is as follows:

[0124]

[0125] The problem of solving the dielectric relaxation time distribution function using the PDC depolarization current is reduced to finding the numerical solution of the linear equation system A*x=b.

[0126] For example, in practical applications, it is impossible to find an analytical expression for the relaxation time distribution function g(τ), and it is necessary to discretize the integral on the left side of the above equation and find its numerical solution. Considering the experimental conditions, the current data before 1s is cut off. The relaxation time constant τ is theoretically continuously distributed, but for representativeness and research convenience, τ is taken as 1-T c The number of data points on the right side of the equation is based on the actual number of measured data points, set to m. Establish an m×100 equation group with 100 variables.

[0127] In step S3, for oil-paper insulation samples in different aging states, the relationship between the probability density peak value in the relaxation time distribution function and the aging state of the oil-paper insulation is constructed to achieve an accurate assessment of the aging degree:

[0128] The PDC curves of oil-paper insulation samples with different aging degrees were tested respectively, and the PDC data were converted into corresponding relaxation time distribution functions. The relationship between the probability density peak and the aging degree was constructed based on the least squares method. The transient and steady-state current characteristics of the tested samples were included in the PDC test results. For the oil-paper insulation samples, the polarization and depolarization times were both 1000s. Keithley 6517A and GPIB IEEE-488 were used to place the oil-paper insulation sample in a three-electrode structure for PDC testing. After a DC voltage U0 was applied to the tested sample, the maintenance time t pol , the current flowing through the medium is the polarization current i pol, remove the external voltage, short-circuit the sample under test, and maintain the time t depol , the current released in the medium is the depolarization current i depol According to the discrete equations, the relaxation time distribution function under the corresponding depolarization current is solved to obtain the aging state evaluation formula of oil-paper insulation:

[0129]

[0130] The accuracy of the evaluation was verified by using new oil-paper insulation samples, and the relative error index was used to measure its accuracy:

[0131]

[0132] Among them, DP is the calculated value of the evaluation model, DP 实测 It is the experimental test value.

[0133] For example, the PDC test results include transient and steady-state current characteristics of the tested sample. According to IEC61620 and IEC60247 standards, for oil-paper insulation samples, the polarization and depolarization time are both 1000s. Keithley6517A and GPIB IEEE-488 are used to place the oil-paper insulation sample in a three-electrode structure for PDC testing. The three-electrode structure avoids the influence of surface leakage current on the tested sample.

[0134] In particular, such as Figure 2 As described above, as the aging degree increases, the depolarization current curve shows an overall increasing trend. The depolarization current curves of different aging degrees have obvious differences, which provides a theoretical basis for using the PDC curve to evaluate the aging state.

[0135] After obtaining the depolarization current of the sample, the corresponding relaxation time distribution function is extracted and calculated as Figure 3 As shown in Figure 2, the main peak moves to the upper left as the aging degree increases. These characteristics are consistent with the influence of aging on PDC.

[0136] On this basis, the relationship curve between the probability density peak and the aging state was obtained as the basis for evaluating the aging degree, such as Figure 4 shown.

[0137] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy, characterized in that: The method comprises the following steps: S1. Construct a distributed Debye model based on dielectric relaxation theory and determine the relaxation time distribution function; S2. Based on the idea of ​​solving a linear equation system, the PDC depolarization current is used to solve the dielectric relaxation time distribution function; S3. For oil-paper insulation samples with different aging states, the relationship between the probability density peak value in the relaxation time distribution function and the aging state of the oil-paper insulation is constructed to achieve accurate evaluation of the aging degree; In step S2, based on the idea of ​​solving a linear equation system, the PDC depolarization current is used to solve the dielectric relaxation time distribution function, which is specifically: In order to determine the relationship between the relaxation time distribution function and the PDC depolarization current curve, a transformation is performed based on the idea of ​​solving a linear equation system: PDC polarization current polarization current i p The relationship with the polarization time t is as follows: Among them U c is the charging voltage, C0 is the geometric capacitance of the sample, σ is the conductivity of the sample, ε0 is the vacuum dielectric constant, f(t) is the relaxation function of the sample, i p It consists of two parts: conduction current and polarization current; The relationship between depolarization current id and discharge time t: i d (t)=-C0U c [f(t)-f(t+T c )] Where T c Represents the charging time, i d It does not contain conductive current, but is only generated by the depolarization process, which is the sum of the discharge currents of various polarization types inside the medium; When the charging cycle is long enough, it can be known from the properties of the dielectric response function: i d (t)=-C0U c [f(t)-f(t+T c )]=-C0U c f(t) Thus there is f(t)=-i d (t) / C0U c The current is reversed f(t)=i' d (t) / C0U c At the same time, through the known relationship: j(t)=dP r / dt=(ε s -ε ∞ )ε0E0f(t) If there is only a single relaxation mechanism in the medium, according to the Debye theory: f(t)=e (-t / τ) / t At this time, g(τ) is a delta function. If there are finite relaxation times in the medium, then g(τ) is g1(τ)=delta(τ) g2(τ)=ρ1delta(τ1)+ρ2delta(τ2) … g n (τ)=ρ1delta(τ1)+ρ2delta(τ2)+…ρ n delta(t n ) at this time, In the limit case, when the τ value is continuously distributed, Calculated Then the relationship between the measured PDC depolarization current and the required relaxation time distribution function g(τ) is simplified to: Since it is impossible to directly obtain the analytical expression of the relaxation time distribution function g(τ), the integral is discretized and its numerical solution is obtained. The current data before 1s is truncated, and τ is taken as 100 points in the logarithm of 1-Tc. The number of equation data points is based on the number obtained by actual measurement, which is set to m. An m×100 equation group with 100 variables is established, and the discretized equation group is as follows: The problem of solving the dielectric relaxation time distribution function using the PDC depolarization current is reduced to finding the numerical solution of the linear equation system A*x=b.

2. According to claim 1, a method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy is characterized in that: In step S1, a distributed Debye model is constructed according to the dielectric relaxation theory, and the relaxation time distribution function is determined as follows: Polarization relaxation time τ is a characteristic time constant that marks the speed of the relaxation polarization process. The larger the τ value, the longer the relaxation polarization process takes to establish and dissipate, and vice versa. The relaxation time τ depends on the characteristics of the dielectric itself and is closely related to the external temperature. As the temperature increases, τ decreases sharply according to the exponential law, which can be expressed as: Where η0 is a constant; a is the dipole radius, m; W η is the activation energy of molecular viscous flow, kJ / mol; For the relaxation process of defect dipole orientation polarization, the relaxation time τ depends on the properties of the crystal and its defects and the external temperature, and changes exponentially with temperature: Where, ν is the ion thermal vibration frequency, Hz; U is the ion activation energy, kJ / mol; When the polarization is provided by multiple relaxation motions with similar relaxation times, P r (t) can be expressed as the relaxation time τ i Unequal polarization components P ri (t) Sum: In order to indicate that the relaxation time τ takes continuous values ​​in the range of 0 to ∞, the distribution function g(τ) is used to represent the distribution of τ. g(τ) is the probability density of the relaxation time distribution, and g(τ)dτ represents the probability that the relaxation time is in the range of τ to τ+dτ. From the probability point of view, the relaxation time distribution function is normalized, that is, g(τ) is:

3. The method for accurately evaluating the aging degree of oil-paper insulation based on time-domain dielectric spectroscopy according to claim 1 is characterized in that: In step S3, for oil-paper insulation samples in different aging states, the relationship between the probability density peak value in the relaxation time distribution function and the aging state of the oil-paper insulation is constructed to achieve an accurate assessment of the aging degree: The PDC curves of oil-paper insulation samples with different aging degrees were tested respectively, and the PDC data were converted into corresponding relaxation time distribution functions. The relationship between the probability density peak and the aging degree was constructed based on the least squares method. The transient and steady-state current characteristics of the tested samples were included in the PDC test results. For the oil-paper insulation samples, the polarization and depolarization times were both 1000s. Keithley 6517A and GPIB IEEE-488 were used to place the oil-paper insulation sample in a three-electrode structure for PDC testing. After a DC voltage U0 was applied to the tested sample, the maintenance time t pol , the current flowing through the medium is the polarization current i pol , remove the external voltage, short-circuit the sample under test, and maintain the time t depol , the current released in the medium is the depolarization current i depol According to the discrete equations, the relaxation time distribution function under the corresponding depolarization current is solved to obtain the aging state evaluation formula of oil-paper insulation: The accuracy of the evaluation was verified by using new oil-paper insulation samples, and the relative error index was used to measure its accuracy: Among them, DP is the calculated value of the evaluation model, DP 实测 It is the experimental test value.

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