A method, apparatus, and storage medium for evaluating the insulation condition of a transformer under high voltage.

Abstract

This invention discloses a method for evaluating the insulation condition of oil-immersed power transformers under high-voltage excitation, belonging to the field of insulation material aging detection technology. The method includes testing the dielectric response of oil-paper insulation under single triangular wave excitation, obtaining multiple harmonics through spectral analysis, and performing Fourier decomposition transform to obtain excitation and response signals under different harmonics. Based on the phase difference between the excitation and response signals, the loss factor of each harmonic at that frequency point is obtained. The above steps are repeated to complete the testing of all frequency points within a preset frequency range. An aging determination coefficient is extracted from the obtained frequency-domain dielectric response loss factor. Through fitting calculation, a quantitative characterization relationship between the aging determination coefficient γ and the degree of aging of the oil-paper insulation is obtained, achieving rapid detection under high-voltage excitation and eliminating the influence of nonlinear insulation changes on insulation condition assessment.

Description

Technical Field

[0001] This invention belongs to the field of insulation material aging detection technology, and in particular relates to a method, apparatus and storage medium for evaluating the insulation status of transformers under high voltage. Background Technology

[0002] With the rapid development of my country's economy, the demand for electricity and energy is increasing, requiring high stability and reliability of the power system during power transmission. As the core component in voltage level transformation and power transmission, the power transformer is one of the most important pieces of equipment for ensuring the safe, reliable, and high-quality operation of the power grid.

[0003] The main cause of power transformer failures is the decline in their insulation performance. The main insulation system of a power transformer consists primarily of an oil-paper insulation system composed of insulating oil and insulating paperboard. Its insulation performance declines exponentially with increasing operating time. Furthermore, external environmental conditions can further accelerate the aging process. Therefore, regularly inspecting the insulation performance of transformers and promptly monitoring their aging status is of paramount importance for maintaining the safe operation of the power grid.

[0004] Currently, most methods for diagnosing the insulation condition of oil-immersed power transformers rely on physicochemical state testing or traditional electrical performance testing methods. Physicochemical state testing primarily involves using liquid chromatography or gas chromatography to measure changes in the physicochemical properties of transformer oil, indirectly assessing the transformer's insulation condition. Alternatively, traditional electrical testing methods such as power frequency dielectric loss testing and partial discharge testing are used to qualitatively analyze the transformer's insulation condition. Currently, frequency domain dielectric response technology is increasingly used to conduct broadband dielectric response tests on transformer insulation. Quantitative analysis of the transformer insulation status is achieved through comparison of characteristic parameters of the curves, integral area values, or basic data. However, experiments have revealed a significant nonlinear variation in the transformer insulation loss factor under different amplitude excitations. Due to the nonlinear characteristics of insulation, accurate insulation status assessment cannot be obtained solely through single-amplitude voltage frequency sweep excitation, resulting in substantial errors. Furthermore, since a single frequency sweep test takes over an hour, multiple frequency sweep tests would severely impact the progress of power grid maintenance. Additionally, the current frequency sweep testing equipment can only reach a peak voltage of 2000 volts, which is insufficient to effectively characterize the insulation characteristics of transformers with higher voltage levels. Existing technologies cannot achieve high-voltage excitation and rapid detection, nor can they eliminate the impact of nonlinear insulation variations on insulation status assessment.

[0005] Therefore, there is an urgent need for a new technical solution to address this problem. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method, apparatus, and storage medium for evaluating the insulation status of oil-immersed power transformers under high-voltage excitation, which solves the problem of rapidly detecting insulation status under high-voltage excitation and eliminating the influence of nonlinear insulation changes on insulation status evaluation.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for evaluating the insulation status of a transformer under high voltage, comprising the following steps.

[0008] Step 1: Obtain the dielectric response curve by testing the dielectric response of the oil-paper insulation under single triangular wave excitation. Based on the spectral analysis of the dielectric response curve, obtain the fundamental, third, fifth, and seventh harmonics of the oil-paper insulation spectrum characteristics.

[0009] Step 2: Perform Fourier decomposition transform on the excitation and response signals to obtain the excitation and response signals under the fundamental, third, fifth, and seventh harmonics as described in Step 1.

[0010] Step 3: Select any point within the preset frequency range, and calculate the loss factor of each harmonic at that frequency point based on the phase difference between the excitation and response signals under different harmonics. Since the amplitude of the harmonics is different, the loss factor of different excitation amplitudes under the same test frequency can be obtained in a single test.

[0011] Step 4: After completing the test at this frequency point, the host computer will automatically switch to the next test frequency point. Repeat the above steps until all frequency points within the preset frequency range are tested, and plot the frequency domain dielectric response loss factor curve within the preset frequency range.

[0012] Step 5: Extract the aging determination coefficient from the frequency domain dielectric response loss factor curve obtained in Step 4. The aging determination coefficient γ is defined as follows:

[0013]

[0014] In the formula, α is the temperature coefficient, T is the ambient temperature of the test, in degrees Celsius, T0 is 25 degrees Celsius, S1 is the integral of the tanδ-f curve under the fundamental frequency over the test frequency range, S2 is the integral of the tanδ-f curve under the third harmonic over the test frequency range, S3 is the integral of the tanδ-f curve under the fifth harmonic over the test frequency range, S4 is the integral of the tanδ-f curve under the seventh harmonic over the test frequency range, U1 is the amplitude of the fundamental voltage, in volts; U3 is the amplitude of the third harmonic voltage, in volts; U5 is the amplitude of the fifth harmonic voltage, in volts; U7 is the amplitude of the seventh harmonic voltage, in volts.

[0015] Step 6: Accelerated aging tests were conducted on oil-paper insulation models with different aging degrees in a laboratory environment. Under the condition of clearly defined insulation aging degree, frequency domain dielectric response tests were performed on the aged samples under triangular wave excitation. The quantitative characterization relationship between the aging determination coefficient γ and the aging degree DP of oil-paper insulation was obtained by fitting calculation.

[0016] The quantitative characterization relationship between the aging determination coefficient γ and the aging degree DP of the oil paper insulation is as follows:

[0017] γ = 912.00502 × e (-DP / 342.49328) -22.67497 3

[0018] In the formula, DP represents the degree of aging of the oil paper insulation.

[0019] Step 7: Based on the value of the aging judgment coefficient γ obtained in Step 5, determine the aging degree of transformer oil paper insulation by means of the quantitative characterization relationship between γ and the aging degree DP of oil paper insulation.

[0020] The preferred method for obtaining the triangular wave excitation in step one is as follows: the AD9833 waveform generation module is connected to a multi-channel cascaded high-voltage amplifier module; the multi-channel cascaded high-voltage amplifier module is connected to the test object; the test object is connected to an I / V conversion sampling unit and a voltage divider; the I / V conversion sampling unit and the voltage divider are connected to an oscilloscope; and the AD9833 waveform generation module and the oscilloscope are connected to a host computer.

[0021] The host computer controls the AD9833 waveform generation module to generate a triangular wave excitation signal via a program. The multi-channel cascaded high-voltage amplifier module is constructed by cascading PA82J modules. The multi-channel cascaded high-voltage amplifier module amplifies the triangular wave excitation signal generated by the AD9833 waveform generation module to achieve the rated test voltage required for testing. The I / V conversion sampling unit uses an electrometer-level operational amplifier to build a phase-shift-free transimpedance amplifier circuit. The high-voltage relay switches the resistance value to realize the acquisition of response micro-current signals. At the same time, in the I / V conversion, the input side adopts a double differential comparison calculation method to eliminate the interference signals of series mode and common mode signals coupled from the outside in the test circuit, so as to realize the accurate acquisition of weak signals in a wide frequency range.

[0022] The preferred host computer uses LabVIEW to set the frequency bandwidth and voltage amplitude of the excitation signal, with a test frequency range of 0.01–1000 Hz and a voltage output range of 0–20 V. The multi-channel cascaded high-voltage amplifier module amplifies the triangular wave excitation signal by 3000 times to reach the rated test voltage.

[0023] In the preferred step two, the excitation and response signal waveform sampling is based on a multiple simultaneous sampling calculation method to obtain accurate high-frequency voltage and current synchronous waveforms on the host computer, thereby improving the accuracy of sampling comparison. Excitation and response signals under different harmonic excitations of different amplitudes are obtained through high-precision Fourier decomposition.

[0024] An apparatus for evaluating the insulation state of a transformer under high voltage, used to implement the aforementioned method for evaluating the insulation state of a transformer under high voltage, includes a triangular wave excitation unit, a spectrum analysis unit, a data conversion unit, a calculation unit, a control unit, and an oil-paper insulation model; the triangular wave excitation unit is used to test the dielectric response of the oil-paper insulation under a single triangular wave excitation to obtain the dielectric response curve;

[0025] The spectrum analysis unit is used to obtain the fundamental, third, fifth, and seventh harmonics of the spectral characteristics of oil-paper insulation based on the dielectric response curve.

[0026] The data conversion unit is used to perform Fourier decomposition transform on the excitation and response signals to obtain the excitation and response signals under the fundamental, third harmonic, fifth harmonic, and seventh harmonic.

[0027] The calculation unit is used to select any point within a preset frequency range and calculate the loss factor of each harmonic at that frequency point based on the phase difference between the excitation and response signals under different harmonics.

[0028] The control unit is used to automatically switch to the next test frequency point under the control of the host computer 1, repeat the above steps until the test of all frequency points within the preset frequency range is completed, and plot the frequency domain dielectric response loss factor curve within the preset frequency range.

[0029] The calculation unit is used to extract the aging determination coefficient from the frequency domain dielectric response loss factor curve.

[0030] The oil-paper insulation model is used to conduct accelerated aging tests on oil-paper insulation models with different aging degrees in a laboratory environment. Under the condition of clearly defined insulation aging degree, the frequency domain dielectric response test of the aged sample under triangular wave excitation is carried out. The quantitative characterization relationship between the aging determination coefficient γ and the aging degree DP of oil-paper insulation is obtained by fitting calculation.

[0031] The preferred triangular wave excitation unit includes: a waveform generation module, a multi-channel cascaded high-voltage amplifier module, a test object, an I / V conversion sampling unit, a voltage divider, and an oscilloscope; the waveform generation module is connected to the multi-channel cascaded high-voltage amplifier module; the multi-channel cascaded high-voltage amplifier module is connected to the test object; the test object is connected to both the I / V conversion sampling unit and the voltage divider; the I / V conversion sampling unit and the voltage divider are connected to the oscilloscope; and the waveform generation module and the oscilloscope are connected to a host computer.

[0032] A computer-readable storage medium for storing computer-readable instructions; the computer-readable instructions, when executed, include steps one through seven described above:

[0033] Through the above design scheme, the present invention can bring the following beneficial effects:

[0034] 1. With just one test, the response voltage and excitation voltage curves of the fundamental, third, fifth and seventh harmonics can be obtained, and the loss factor curves under different excitation amplitudes can be obtained, reducing the test time by 75%.

[0035] 2. Effectively eliminates the influence of the nonlinear dielectric properties of oil-paper insulation under different excitation amplitudes on the evaluation results;

[0036] 3. By calculating the value of the aging determination coefficient γ, the degree of aging of the transformer can be quantitatively analyzed based on its fitting relationship with the degree of polymerization.

[0037] 4. A temperature correction factor α was introduced, which greatly improved the accuracy of the testing device in low-temperature environments.

[0038] 5. In I / V conversion, a double differential comparison calculation method is used on the input side to eliminate interference signals from external coupled series and common-mode signals in the test circuit, thereby achieving accurate acquisition of weak signals over a wide frequency range.

[0039] 6. The excitation and response signal waveform sampling is based on a multiple simultaneous sampling calculation method to achieve accurate synchronous waveforms of high-frequency voltage and current on the host computer, thereby improving the accuracy of sampling comparison. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the triangular wave excitation unit of a device for evaluating the insulation state of a transformer under high voltage according to the present invention.

[0041] Figure 2 This is a flowchart of a method for evaluating the insulation status of a transformer under high voltage according to the present invention.

[0042] Figure 3The diagram shows a triangular wave excitation signal with an amplitude of 9 kV at 110 Hz, which is part of the method for evaluating the insulation status of a transformer under high voltage according to the present invention.

[0043] Figure 4 The frequency domain analytical spectrum of a triangular wave excitation signal with an amplitude of 9 kV at 110 Hz is shown in the present invention, which is a method for evaluating the insulation state of a transformer under high voltage.

[0044] Figure 5 The diagram shows the triangular wave excitation signal and response signal with an amplitude of 9 kV, which is part of the method for evaluating the insulation status of a transformer under high voltage according to the present invention.

[0045] Figure 6 The graph shows the dielectric loss factor of the fundamental wave and each harmonic under a 9 kV triangular wave excitation signal, which is a method for evaluating the insulation status of a transformer under high voltage according to the present invention.

[0046] Figure 7 This is a graph showing the fitting relationship between the aging determination coefficient γ and the degree of polymerization of the insulating paperboard in a method for evaluating the insulation status of a transformer under high voltage according to the present invention.

[0047] Figure 8 This is a schematic diagram of the structure of a device for evaluating the insulation status of a transformer under high voltage according to the present invention.

[0048] In the diagram, 1-host computer, 2-waveform generation module, 3-multi-channel cascaded high-voltage amplifier module, 4-test sample, 5-I / V conversion sampling unit, 6-voltage divider, 7-oscilloscope, 10-triangular wave excitation unit, 20-spectral analysis unit, 30-spectral analysis unit, 40-calculation unit, 50-control unit, and 60-oil paper insulation model. Detailed Implementation

[0049] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0050] 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.

[0051] 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.

[0052] From the appendix Figures 1-8 The following steps are shown: A method for evaluating the insulation condition of a transformer under high voltage.

[0053] Step 1: Obtain the dielectric response curve by testing the dielectric response of the oil-paper insulation under single triangular wave excitation. Based on the spectral analysis of the dielectric response curve, obtain the fundamental, third, fifth, and seventh harmonics of the oil-paper insulation spectrum characteristics.

[0054] Step 2: Perform Fourier decomposition transform on the excitation and response signals to obtain the excitation and response signals under the fundamental, third, fifth, and seventh harmonics as described in Step 1.

[0055] Step 3: Select any point within the preset frequency range, and calculate the loss factor of each harmonic at that frequency point based on the phase difference between the excitation and response signals under different harmonics. Since the amplitude of the harmonics is different, the loss factor of different excitation amplitudes under the same test frequency can be obtained in a single test.

[0056] Step 4: After completing the test at this frequency point, the host computer 1 will automatically switch to the next test frequency point and repeat the above steps until all frequency points within the preset frequency range are tested and the frequency domain dielectric response loss factor curve within the preset frequency range is plotted.

[0057] Step 5: Extract the aging determination coefficient from the frequency domain dielectric response loss factor curve obtained in Step 4. The aging determination coefficient γ is defined as follows:

[0058]

[0059]

[0060] In the formula, α is the temperature coefficient, T is the ambient temperature of the test, in degrees Celsius, T0 is 25 degrees Celsius, S1 is the integral of the tanδ-f curve under the fundamental frequency over the test frequency range, S2 is the integral of the tanδ-f curve under the third harmonic over the test frequency range, S3 is the integral of the tanδ-f curve under the fifth harmonic over the test frequency range, S4 is the integral of the tanδ-f curve under the seventh harmonic over the test frequency range, U1 is the amplitude of the fundamental voltage, in volts; U3 is the amplitude of the third harmonic voltage, in volts; U5 is the amplitude of the fifth harmonic voltage, in volts; U7 is the amplitude of the seventh harmonic voltage, in volts.

[0061] Step 6: Accelerated aging tests were conducted on oil-paper insulation models with different aging degrees in a laboratory environment. Under the condition of clearly defined insulation aging degree, frequency domain dielectric response tests were performed on the aged samples under triangular wave excitation. The quantitative characterization relationship between the aging determination coefficient γ and the aging degree DP of oil-paper insulation was obtained by fitting calculation.

[0062] γ = 912.00502 × e (-DP / 342.49328)-22.67497 3

[0063] In the formula, DP represents the degree of aging of the oil paper insulation.

[0064] Step 7: Based on the value of the aging judgment coefficient γ obtained in Step 5, determine the degree of aging of the transformer oil paper insulation using Formula 3.

[0065] The further step in obtaining the triangular wave excitation is as follows: the AD9833 waveform generation module 2 is connected to the multi-channel cascaded high-voltage amplifier module 3; the multi-channel cascaded high-voltage amplifier module 3 is connected to the test object 4; the test object 4 is connected to the I / V conversion sampling unit 5 and the voltage divider 6 respectively; the I / V conversion sampling unit 5 and the voltage divider 6 are respectively connected to the oscilloscope 7; the AD9833 waveform generation module 2 and the oscilloscope 7 are respectively connected to the host computer 1.

[0066] The host computer 1 controls the AD9833 waveform generation module 2 to generate a triangular wave excitation signal via a program. The multi-channel cascaded high-voltage amplifier module 3 is constructed by cascading PA82J modules. The multi-channel cascaded high-voltage amplifier module 3 amplifies the triangular wave excitation signal generated by the AD9833 waveform generation module 2 to achieve the rated test voltage required for testing. The I / V conversion sampling unit 5 uses an electrometer-level operational amplifier to build a phase-shift-free transimpedance amplifier circuit. Through multi-channel switching by a high-voltage relay, the resistance value is changed to achieve the acquisition of the response micro-current signal. Simultaneously, in the I / V conversion, a double differential comparison calculation method is used on the input side to eliminate interference signals from externally coupled series-mode and common-mode signals in the test circuit, achieving accurate acquisition of weak signals over a wide frequency range. The acquisition current range is 1×10⁻⁶. -15 Up to 1×10 -8 Amperes, sampling frequency range in 10 -2 ~10 3 hertz.

[0067] The host computer 1 further sets the frequency bandwidth and voltage amplitude of the excitation signal through a LabVIEW program. The test frequency range is 0.01 to 1000 Hz, and the voltage output range is 0 to 20 V. The host computer controls the digital signal generator to generate a triangular wave excitation signal with a precision of 16 bits through AT commands.

[0068] The multi-channel cascaded high-voltage amplifier module 3 amplifies the triangular wave excitation signal by 3000 times to reach the rated test voltage.

[0069] In the further step two, the sampling of the excitation and response signal waveforms is based on a multiple simultaneous sampling calculation method to achieve accurate high-frequency voltage and current synchronous waveforms on the host computer 1, thereby improving the accuracy of sampling comparison. Excitation and response signals under different harmonic excitations of different amplitudes are obtained through high-precision Fourier decomposition.

[0070] A device for evaluating the insulation state of a transformer under high voltage includes a triangular wave excitation unit 10, a spectrum analysis unit 20, a data conversion unit 30, a calculation unit 40, a control unit 50, and an oil-paper insulation model 60; the triangular wave excitation unit 10 is used to test the dielectric response of the oil-paper insulation under a single triangular wave excitation to obtain the dielectric response curve.

[0071] The spectrum analysis unit 20 is used to obtain the fundamental, third, fifth, and seventh harmonics of the spectrum characteristics of the oil-paper insulation based on the spectrum analysis of the dielectric response curve.

[0072] The data conversion unit 30 is used to perform Fourier decomposition transform on the excitation and response signals to obtain the excitation and response signals under the fundamental, third harmonic, fifth harmonic, and seventh harmonic.

[0073] The calculation unit 40 is used to select any point within a preset frequency range and calculate the loss factor of each harmonic at that frequency point based on the phase difference between the excitation and response signals under different harmonics.

[0074] The control unit 50 is used to automatically switch to the next test frequency point under the control of the host computer 1, repeat the above steps until the test of all frequency points within the preset frequency range is completed, and plot the frequency domain dielectric response loss factor curve within the preset frequency range.

[0075] The calculation unit 40 is used to extract the aging determination coefficient from the frequency domain dielectric response loss factor curve.

[0076] The oil-paper insulation model 60 is used to conduct accelerated aging tests on oil-paper insulation models with different aging degrees in a laboratory environment. Under the condition of clearly defined insulation aging degree, the frequency domain dielectric response test of the aged sample under triangular wave excitation is carried out. The quantitative characterization relationship between the aging determination coefficient γ and the aging degree DP of the oil-paper insulation is obtained by fitting calculation.

[0077] The triangular wave excitation unit 10 further includes: a waveform generation module 2, a multi-channel cascaded high-voltage amplifier module 3, a test object 4, an I / V conversion sampling unit 5, a voltage divider 6, and an oscilloscope 7; the waveform generation module 2 is connected to the multi-channel cascaded high-voltage amplifier module 3; the multi-channel cascaded high-voltage amplifier module 3 is connected to the test object 4; the test object 4 is connected to both the I / V conversion sampling unit 5 and the voltage divider 6; the I / V conversion sampling unit 5 and the voltage divider 6 are connected to the oscilloscope 7; and the waveform generation module 2 and the oscilloscope 7 are connected to the host computer 1.

[0078] A computer-readable storage medium for storing computer-readable instructions; the computer-readable instructions, when executed, include steps one through seven described above:

[0079] In practice, on the interface of the host computer 1, the test frequency range, signal bandwidth, and voltage amplitude are selected. After the test starts, the signal generator receives the instruction from the host computer 1 and sends out the corresponding triangular wave excitation signal. In this embodiment, the applied frequency values ​​are 1000, 470, 220, 110, 70, 40, 20, 10, 4.6, 2.2, 1, 0.46, 0.22, 0.1, 0.046, 0.022, and 0.01 Hz. Taking 110 Hz as an example, the triangular wave voltage waveform is as follows: Figure 3 As shown, the frequency domain analytical spectrum of the excitation voltage is as follows: Figure 4 As shown, the multi-channel cascaded linear high-voltage amplifier module 3 amplifies the 3V triangular wave excitation signal by 3000 times to reach the rated test voltage of 9000V, which is then applied to the test object 4. The I / V conversion sampling unit 5, through automatic transimpedance adjustment, matches different discharge transimpedances at different test frequencies to achieve micro-current testing over a wide frequency band, and converts it into a voltage signal, which is then transmitted to the oscilloscope 7. The voltage divider 6 is connected in parallel with the test object 4, and the excitation voltage signal is transmitted to the oscilloscope 7 after passing through the voltage divider 6. The waveforms of the excitation voltage and response voltage received by the oscilloscope 7 are shown below. Figure 5 As shown, the host computer 1 performs high-precision Fourier analysis on the waveform data to obtain the curves showing the variation of the loss factor of the insulating material under triangular wave excitation with the test frequency for the fundamental, third, fifth, and seventh harmonics. After obtaining the tanδ-f curves for each harmonic, the curves for each harmonic are integrated within the test frequency range to obtain S1, S2, and S3. Then, the aging determination coefficient γ is calculated using the definition of aging determination coefficient γ. Finally, based on γ, a quantitative assessment of the aging degree of the transformer is achieved.

[0080] A 35kV oil-immersed transformer that had been decommissioned and used for 25 years was selected as the test specimen. Frequency domain dielectric response tests were conducted on the transformer under a 0-degree Celsius test environment. After the test, spectral analysis yielded frequency domain dielectric loss factor curves under different harmonics, as shown below. Figure 6 As shown, for Figure 6 The tanδ-f curves under each harmonic are integrally processed, and the results are as follows: Figure 7 As shown. The calculated aging determination coefficient γ is 253.6, and the calculated DP value is 409. According to power industry standards, when the degree of polymerization of the insulating paperboard inside the transformer drops to around 500, the dielectric loss of the insulating paperboard increases, the breakdown field strength decreases to a certain extent, and the mechanical properties will decline significantly. At this point, the insulating paperboard inside the transformer can be considered to have reached the middle of its aging life. When the degree of polymerization is between 350 and 450, the degradation of the insulating paper is close to the critical point, and it is recommended to resample and test within 1 to 2 years.

[0081] 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 insulation condition of a transformer under high voltage, characterized in that, Includes the following steps, Step 1: Obtain the dielectric response curve by testing the dielectric response of the oil-paper insulation under single triangular wave excitation. Based on the spectral analysis of the dielectric response curve, obtain the fundamental, third, fifth, and seventh harmonics of the oil-paper insulation spectrum characteristics. Step 2: Perform Fourier decomposition transform on the excitation and response signals to obtain the excitation and response signals under the fundamental, third, fifth, and seventh harmonics as described in Step 1. Step 3: Select any point within the preset frequency range, and calculate the loss factor of each harmonic at that frequency point based on the phase difference between the excitation and response signals under different harmonics. Step 4: After completing the test at this frequency point, the host computer (1) automatically switches to the next test frequency point and repeats the above steps until the test of all frequency points within the preset frequency range is completed, and the frequency domain dielectric response loss factor curve within the preset frequency range is plotted. Step 5: Extract the aging determination coefficient from the frequency domain dielectric response loss factor curve obtained in Step 4. The aging determination coefficient γ is defined as follows: In the formula, α is the temperature coefficient, T is the ambient temperature of the test, in degrees Celsius, T0 is 25 degrees Celsius, S1 is the integral of the tanδ-f curve under the fundamental frequency over the test frequency range, S2 is the integral of the tanδ-f curve under the third harmonic over the test frequency range, S3 is the integral of the tanδ-f curve under the fifth harmonic over the test frequency range, S4 is the integral of the tanδ-f curve under the seventh harmonic over the test frequency range, and U1 is the amplitude of the fundamental voltage, in volts. U3 is the amplitude of the third harmonic voltage, in volts; U5 is the amplitude of the fifth harmonic voltage, in volts. U7 is the amplitude of the seventh harmonic voltage, in volts. Step 6: Accelerated aging tests were conducted on oil-paper insulation models with different aging degrees in a laboratory environment. Under the condition of clearly defined insulation aging degree, frequency domain dielectric response tests were performed on the aged samples under triangular wave excitation. The quantitative characterization relationship between the aging determination coefficient γ and the aging degree DP of oil-paper insulation was obtained by fitting calculation. The quantitative characterization relationship between the aging determination coefficient γ and the aging degree DP of the oil paper insulation is as follows: γ=912.00502×e (-DP / 342.49328) -22.67497 (3) In the formula, DP represents the degree of aging of the oil paper insulation; Step 7: Based on the value of the aging judgment coefficient γ obtained in Step 5, determine the aging degree of transformer oil paper insulation by means of the quantitative characterization relationship between γ and the aging degree DP of oil paper insulation.

2. The method for evaluating the insulation status of a transformer under high voltage according to claim 1, characterized in that, The triangular wave excitation in step one is obtained as follows: the waveform generation module (2) is connected to the multi-channel cascaded high-voltage amplifier module (3); the multi-channel cascaded high-voltage amplifier module (3) is connected to the test object (4); the test object (4) is connected to the I / V conversion sampling unit (5) and the voltage divider (6) respectively; the I / V conversion sampling unit (5) and the voltage divider (6) are connected to the oscilloscope (7) respectively; the waveform generation module (2) and the oscilloscope (7) are connected to the host computer (1) respectively. The host computer (1) generates a triangular wave excitation signal through the waveform generation module (2) controlled by the program; the multi-channel cascaded high voltage amplification module (3) is constructed by cascading PA82J modules. The multi-channel cascaded high voltage amplification module (3) amplifies the triangular wave excitation signal generated by the AD9833 waveform generation module (2) to achieve the rated test voltage required for the test; the I / V conversion sampling unit (5) uses an electrometer-level operational amplifier to build a phase-shift-free transimpedance amplifier circuit. The high voltage relay switches the resistance value to realize the acquisition of the response micro current signal. At the same time, in the I / V conversion, the input side adopts the double differential comparison calculation method to eliminate the interference signal of series mode and common mode signals coupled from the outside in the test circuit, so as to realize the accurate acquisition of weak signals in a wide frequency range.

3. The method for evaluating the insulation status of a transformer under high voltage according to claim 2, characterized in that, The host computer (1) sets the frequency bandwidth and voltage amplitude of the excitation signal through the program. The test frequency range is 0.01 to 1000 Hz, and the voltage output range is 0 to 20 V. The multi-channel cascaded high voltage amplifier module (3) amplifies the triangular wave excitation signal by 3000 times to reach the rated test voltage.

4. The method for evaluating the insulation status of a transformer under high voltage according to claim 1, characterized in that, Step 2 describes the sampling of excitation and response signal waveforms based on a multiple simultaneous sampling calculation method. This enables the acquisition of accurate high-frequency voltage and current synchronous waveforms on the host computer (1), improving the accuracy of sampling comparison. High-precision Fourier decomposition is used to obtain excitation and response signals under different harmonic excitations of varying amplitudes.

5. An apparatus for evaluating the insulation condition of a transformer under high voltage, used to implement the method for evaluating the insulation condition of a transformer under high voltage as described in claim 1, characterized in that, It includes a triangular wave excitation unit (10), a spectrum analysis unit (20), a data conversion unit (30), a calculation unit (40), a control unit (50), and an oil-paper insulation model (60); the triangular wave excitation unit (10) is used to test the dielectric response of oil-paper insulation under a single triangular wave excitation to obtain the dielectric response curve; The spectrum analysis unit (20) is used to obtain the fundamental, third, fifth, and seventh harmonics of the oil paper insulation spectrum characteristics based on the spectrum analysis of the dielectric response curve. The data conversion unit (30) is used to perform Fourier decomposition transformation on the excitation and response signals to obtain the excitation and response signals under the fundamental, third harmonic, fifth harmonic and seventh harmonic. The calculation unit (40) is used to select any point within a preset frequency range and calculate the loss factor of each harmonic at that frequency point based on the phase difference between the excitation and response signals under different harmonics. The control unit (50) is used to automatically switch to the next test frequency point under the control of the host computer (1), repeat the above steps until the test of all frequency points within the preset frequency range is completed, and draw the frequency domain dielectric response loss factor curve within the preset frequency range. The calculation unit (40) is used to extract the aging determination coefficient from the frequency domain dielectric response loss factor curve; The oil-paper insulation model (60) is used to conduct accelerated aging tests on oil-paper insulation models with different aging degrees in a laboratory environment. Under the condition of clearly defined insulation aging degree, the frequency domain dielectric response test of the aged sample under triangular wave excitation is carried out. The quantitative characterization relationship between the aging determination coefficient γ and the aging degree DP of oil-paper insulation is obtained by fitting calculation.

6. The apparatus for evaluating the insulation condition of a transformer under high voltage according to claim 5, characterized in that, The triangular wave excitation unit (10) includes: a waveform generation module (2), a multi-channel cascaded high-voltage amplifier module (3), a test object (4), an I / V conversion sampling unit (5), a voltage divider (6), and an oscilloscope (7); the waveform generation module (2) is connected to the multi-channel cascaded high-voltage amplifier module (3); the multi-channel cascaded high-voltage amplifier module (3) is connected to the test object (4); the test object (4) is connected to the I / V conversion sampling unit (5) and the voltage divider (6) respectively; the I / V conversion sampling unit (5) and the voltage divider (6) are connected to the oscilloscope (7) respectively; the waveform generation module (2) and the oscilloscope (7) are connected to the host computer (1) respectively.

7. The apparatus for evaluating the insulation condition of a transformer under high voltage according to claim 6, characterized in that, The host computer (1) sets the frequency bandwidth and voltage amplitude of the excitation signal through a program. The test frequency range is 0.01 to 1000 Hz, and the voltage output range is 0 to 20 V. The multi-channel cascaded high voltage amplifier module (3) amplifies the triangular wave excitation signal by 3000 times to reach the rated test voltage.

8. A computer-readable storage medium, characterized in that, Used to store computer-readable instructions; when executed, the computer-readable instructions include steps one through seven as described in any one of claims 1 to 4.

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