Nondestructive testing method and equipment for aging degree of insulating oil, medium and product

Abstract

The invention discloses a nondestructive testing method and device for the aging degree of insulating oil, a medium and a product, and relates to the field of insulating oil quality evaluation. The method comprises the following steps: firstly, carrying out in-situ windowing on the oil-immersed transformer, and carrying out a terahertz test on insulating oil flowing through a window to obtain a terahertz time-domain spectrum; then, Fourier transform is adopted to convert the terahertz time-domain spectrum into a terahertz frequency-domain spectrum, and a terahertz absorption coefficient is calculated; calculating a terahertz absorption coefficient integral value according to the terahertz absorption coefficient; substituting the terahertz absorption coefficient integral value into a power frequency dielectric loss model, and calculating the current power frequency dielectric loss; and the aging degree of the insulating oil is determined according to the current power frequency dielectric loss, so that efficient, convenient, non-contact and nondestructive detection of the aging degree of the insulating oil can be realized.

Description

Technical Field

[0001] The present application relates to the technical field of insulating oil quality evaluation, and particularly to a non-destructive detection method, device, medium and product for the aging degree of insulating oil. Background Art

[0002] As the core device for power conversion in the power grid, the operation reliability of oil-immersed power transformers directly affects the power supply quality and safety level of the grid. Industry failure statistics reveal that more than about 52% of transformer shutdown failures can be traced back to the performance degradation of the oil-paper composite insulation system, and the performance of insulating oil directly affects the safe operation and reliability of transformer equipment. This makes it an important technical issue to build an effective insulation state evaluation system to ensure the safe operation of power equipment, and it has important engineering application value for realizing grid fault warning and extending the service life of equipment.

[0003] Insulating oil will age during long-term use, resulting in a decline in its performance. The current insulating oil quality evaluation system mainly relies on the detection of conventional physical and chemical indexes such as the dielectric loss factor and micro water content. The testing of these traditional parameters depends on cumbersome sample processing and slow testing processes, and the sampling and testing processes are destructive, making it difficult to meet the technical requirements of real-time monitoring in smart grids. Summary of the Invention

[0004] The purpose of the present application is to provide a non-destructive detection method, device, medium and product for the aging degree of insulating oil, so as to realize efficient, convenient, non-contact and non-destructive detection of the aging degree of insulating oil.

[0005] To achieve the above purpose, the present application provides the following solutions.

[0006] In the first aspect, the present application provides a non-destructive detection method for the aging degree of insulating oil, including:

[0007] Performing in-situ windowing on an oil-immersed transformer, and performing terahertz testing on the insulating oil flowing through the window to obtain a terahertz time-domain spectrum;

[0008] Using Fourier transform to convert the terahertz time-domain spectrum into a terahertz frequency-domain spectrum, and calculating the terahertz absorption coefficient;

[0009] Calculating the integral value of the terahertz absorption coefficient according to the terahertz absorption coefficient;

[0010] Substituting the integral value of the terahertz absorption coefficient into the power frequency dielectric loss model to calculate the current power frequency dielectric loss;

[0011] Determining the aging degree of the insulating oil according to the current power frequency dielectric loss.

[0012] Optionally, perform terahertz testing on the insulating oil flowing through the window to obtain a terahertz time-domain spectrum, specifically including:

[0013] Use a transmission terahertz time-domain spectroscopy system to perform terahertz testing on the insulating oil flowing through the window to obtain a terahertz time-domain spectrum; the abscissa of the terahertz time-domain spectrum is time, and the ordinate is the time-domain signal.

[0014] Optionally, the transmission terahertz time-domain spectroscopy system includes: a femtosecond laser, a beam splitter, a time delay device, a reflector, a terahertz emitter, a terahertz detector, a first parabolic mirror, a second parabolic mirror, a lock-in amplifier, and a PC control terminal;

[0015] The beam splitter is located on the outgoing optical path of the femtosecond laser; the laser pulse emitted by the femtosecond laser is split into a pump beam and a probe beam by the beam splitter;

[0016] The terahertz emitter is located on the reflected optical path of the beam splitter; the pump beam reflected by the beam splitter is incident on the terahertz emitter, and a terahertz pulse is generated by the terahertz emitter;

[0017] The first parabolic mirror is located on the outgoing optical path of the terahertz emitter, and is used to focus the terahertz pulse generated by the terahertz emitter onto the window of the oil-immersed transformer;

[0018] The second parabolic mirror is located on the transmitted optical path of the insulating oil at the window, and is used to re-collect and focus the terahertz pulse transmitted through the insulating oil onto the terahertz detector;

[0019] The time delay device is located on the transmitted optical path of the beam splitter; the probe beam transmitted through the beam splitter is incident on the reflector after passing through the time delay device, and is reflected by the reflector onto the terahertz detector;

[0020] The terahertz detector is connected to the PC control terminal via a lock-in amplifier; the PC control terminal is used to generate the terahertz time-domain spectrum of the insulating oil according to the terahertz pulse signal and the probe beam signal received by the terahertz detector.

[0021] Optionally, use Fourier transform to convert the terahertz time-domain spectrum into a terahertz frequency-domain spectrum, and calculate the terahertz absorption coefficient, specifically including:

[0022] Use Fourier transform to convert the terahertz time-domain spectrum into a terahertz frequency-domain waveform; the abscissa of the terahertz frequency-domain waveform is frequency, and the ordinate is the frequency-domain amplitude;

[0023] According to the frequency-domain amplitude of the terahertz frequency-domain waveform, use the formula to calculate the terahertz absorption coefficient α(ω) at frequency ω; where n sRe(n)(ω) represents the real part of the refractive index at frequency ω, and Im(n)(ω) represents the imaginary part of the refractive index at frequency ω; c is the propagation speed of terahertz waves in air; d is the thickness of the insulating oil sample; A(ω) is the frequency-domain amplitude at frequency ω.

[0024] Optionally, calculating the integral value of the terahertz absorption coefficient according to the terahertz absorption coefficient specifically includes:

[0025] According to the terahertz absorption coefficient α(ω) at frequency ω, using the formula to calculate the integral value S of the terahertz absorption coefficient α ; where ω1 is the lower frequency limit; ω2 is the upper frequency limit.

[0026] Optionally, substituting the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model to calculate the current power-frequency dielectric loss specifically includes:

[0027] Substitute the integral value S of the terahertz absorption coefficient α into the power-frequency dielectric loss model Tanδ = 0.08364S α + 0.00818 to calculate the current power-frequency dielectric loss Tanδ.

[0028] Optionally, determining the aging degree of the insulating oil according to the current power-frequency dielectric loss specifically includes:

[0029] The greater the current power-frequency dielectric loss Tanδ, the higher the determined aging degree of the current insulating oil.

[0030] In a second aspect, the present application provides a computer device, including: a memory, a processor, and a computer program stored on the memory and executable on the processor, where the processor executes the computer program to implement a non-destructive detection method for the aging degree of insulating oil;

[0031] The non-destructive detection method for the aging degree of insulating oil includes:

[0032] Obtain the terahertz time-domain spectrum of the insulating oil in the oil-immersed transformer;

[0033] Use Fourier transform to convert the terahertz time-domain spectrum into a terahertz frequency-domain spectrum and calculate the terahertz absorption coefficient;

[0034] Calculate the integral value of the terahertz absorption coefficient according to the terahertz absorption coefficient;

[0035] Substitute the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model to calculate the current power-frequency dielectric loss;

[0036] Determine the aging degree of the insulating oil according to the current power-frequency dielectric loss.

[0037] In a third aspect, the present application provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, a non-destructive detection method for the aging degree of insulating oil is implemented;

[0038] The non-destructive detection method for the aging degree of insulating oil includes:

[0039] Obtain the terahertz time-domain spectrum of the insulating oil in the oil-immersed transformer;

[0040] Use Fourier transform to convert the terahertz time-domain spectrum into a terahertz frequency-domain spectrum, and calculate the terahertz absorption coefficient;

[0041] Calculate the integral value of the terahertz absorption coefficient according to the terahertz absorption coefficient;

[0042] Substitute the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model to calculate the current power-frequency dielectric loss;

[0043] Determine the aging degree of the insulating oil according to the current power-frequency dielectric loss.

[0044] In a fourth aspect, the present application provides a computer program product, including a computer program. When the computer program is executed by a processor, a non-destructive detection method for the aging degree of insulating oil is implemented;

[0045] The non-destructive detection method for the aging degree of insulating oil includes:

[0046] Obtain the terahertz time-domain spectrum of the insulating oil in the oil-immersed transformer;

[0047] Use Fourier transform to convert the terahertz time-domain spectrum into a terahertz frequency-domain spectrum, and calculate the terahertz absorption coefficient;

[0048] Calculate the integral value of the terahertz absorption coefficient according to the terahertz absorption coefficient;

[0049] Substitute the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model to calculate the current power-frequency dielectric loss;

[0050] Determine the aging degree of the insulating oil according to the current power-frequency dielectric loss.

[0051] According to the specific embodiments provided by the present application, the following technical effects are disclosed in the present application.

[0052] A non-destructive testing method, device, medium and product for the aging degree of insulating oil provided by this application can directly perform terahertz testing on the insulating oil in a running transformer, obtain its terahertz time-domain spectrum, and then calculate the current power-frequency dielectric loss according to the power-frequency dielectric loss model, thereby determining the aging degree of the insulating oil, realizing real-time, non-contact and non-destructive testing of the aging degree of insulating oil, and the testing process is very convenient, greatly improving the detection efficiency of the aging degree of insulating oil. Description of the Drawings

[0053] In order to more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0054] Figure 1 It is a schematic flow chart of a non-destructive testing method for the aging degree of insulating oil in this application;

[0055] Figure 2 It is a schematic diagram of the change of power-frequency dielectric loss with aging time;

[0056] Figure 3 It is a schematic diagram of the principle of a transmission terahertz time-domain spectroscopy system;

[0057] Figure 4 It is a schematic diagram of the terahertz time-domain spectrum of insulating oil with different aging degrees;

[0058] Figure 5 It is a schematic diagram of the terahertz frequency-domain waveform of insulating oil with different aging degrees;

[0059] Figure 6 It is a schematic diagram of the terahertz frequency-domain spectrum of insulating oil samples with different aging degrees;

[0060] Figure 7 For S α And the power-frequency dielectric loss scatter plot;

[0061] Figure 8 For S α And the fitting straight line schematic diagram of the power-frequency dielectric loss;

[0062] Figure 9 It is a schematic diagram of the terahertz time-domain spectrum of the 130 °C sample;

[0063] Figure 10 It is a schematic diagram of the absorption coefficient of the 130 °C sample;

[0064] Figure 11 It is a schematic diagram of the validation result of the effectiveness of the linear model. Detailed implementation manners

[0065] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0066] The present application provides a non-destructive detection method, device, medium and product for the aging degree of insulating oil, aiming to achieve efficient, convenient, non-contact and non-destructive detection of the aging degree of insulating oil.

[0067] To make the above objects, features and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0068] In an exemplary embodiment, as Figure 1 shown, a non-destructive detection method for the aging degree of insulating oil is provided, including the following steps 1 to 5.

[0069] Before performing the non-destructive detection method for the aging degree of insulating oil in the present application, it is first necessary to determine the power frequency dielectric loss model of the insulating oil. By focusing on the forefront application of terahertz time-domain spectroscopy (THz-TDS) detection technology, based on the unique technical advantages demonstrated by terahertz waves in the field of non-destructive detection of insulating materials, such as generating characteristic absorption peaks in polar dielectrics and maintaining low-attenuation transmission characteristics in non-polar systems, samples with gradient aging degrees were prepared under thermal stress conditions of 120°C and 130°C, and the variation law of the absorption spectrum was obtained using a transmission terahertz time-domain spectroscopy system. A quantitative model of characteristic absorption and aging degree was established using the 120°C sample, and its effectiveness was verified using the 130°C sample, providing a new non-destructive detection scheme for the intelligent diagnosis of the insulation state of transformers. The determination process of the power frequency dielectric loss model of insulating oil in the present application includes the following S1 to S5.

[0070] S1. Prepare insulating oils with different aging degrees.

[0071] The materials for the accelerated thermal aging test are Karamay #25 mineral insulating oil, sulfate cellulose insulating paper (0.12 mm thick) and copper bars (3 mm thick). The test temperatures are respectively selected as 120°C and 130°C. The detailed steps include the following S1.1) to S1.5).

[0072] S1.1) Place the insulating oil in a wide-mouth bottle and vacuum dry the insulating paper and insulating oil at 5 kPa / 90°C for 48 hours and the copper strips for 72 hours to remove as much moisture and oxygen as possible.

[0073] S1.2) Place the insulating paper in mineral insulating oil at a mass ratio of 10:1, so that the insulating oil fully fills the pores of the insulating paper. Vacuum impregnate the paper at 5 kPa / 60°C for 24 hours to further remove moisture and gas.

[0074] S1.3) After vacuum impregnation, 5mm per gram of oil 2 Copper bars are added to form a sample. Each sample typically contains 1 liter of insulating oil and 87 grams of insulating paper. At least two groups should be set up, with at least 7 samples in each group.

[0075] S1.4) Simulate real transformer operating conditions and conduct accelerated thermal aging tests by placing jars containing at least 7 samples in aging chambers at 120°C and 130°C, respectively.

[0076] In a real oil-immersed transformer, insulating oil, insulating paper, and copper conductors coexist and contact each other for a long time. The simultaneous inclusion of all three in the test can simulate their synergistic chemical and physical aging effects: copper catalyzes the oxidation of the insulating oil → the acidic substances generated in the oil (such as low-molecular acids) accelerate the degradation of the insulating paper → the degradation products of the paper further deteriorate the performance of the oil, resulting in a decrease in performance such as power frequency dielectric loss, forming a vicious cycle.

[0077] S1.5) Take out samples regularly on the 2nd, 5th, 8th, 12th, 16th, 20th and 25th day of aging. Take 20ml of insulating oil for each sample and place it in a highly airtight headspace gas phase bottle, seal it with a sealing film, and store it in a constant temperature box at 4°C to prevent the volatilization of polar substances in the oil and further reaction of internal substances (such as water and acid), and ensure that the sample is consistent with the sampling time. Each sample in each group of samples is exactly the same, except for the number of days of thermal aging. After all sampling is completed, terahertz testing is carried out uniformly, and usually seven samples are tested together within one day. The remaining oil sample in each sample is tested according to the national standard for the sample power frequency dielectric loss (abbreviated as power frequency dielectric loss or dielectric loss).

[0078] S2. The test medium loss indicates the aging state.

[0079] Experiments were conducted to obtain 7 gradient-aged samples at 120°C and 130°C respectively. The aging state was represented by the dielectric loss of the insulating oil, and its dielectric loss was measured according to the national standard as shown in Table 1. The dielectric loss test method is usually as follows: According to the national standard GB / T 5654-2007 "Measurement of Relative Permittivity, Dielectric Dissipation Factor and DC Resistivity of Liquid Insulating Materials", first homogenize the oil sample and heat it to 90±5°C and keep it warm; thoroughly clean the electrode cup and rinse it 3 times with the oil to be tested, slowly fill it with the oil sample and remove the air bubbles; use the dielectric loss tester to keep the electrode cup at a constant temperature of 90±1°C, and after stabilization, the dielectric loss tester applies a 50Hz power frequency voltage (usually 2kV) to measure the dielectric dissipation factor tanδ; repeat the test twice, and take the average value as the final result.

[0080] Table 1 Aging time and power frequency dielectric loss of samples

[0081]

[0082] Plot the data in Table 1 as Figure 2 to observe the variation law of dielectric loss with time. It is found that as the aging time increases, the dielectric loss increases, and at the same aging time, the higher the temperature, the greater the power frequency dielectric loss. This is because polar substances are generated in the oil-paper insulation during the aging process and dissolve in the insulating oil. The polar substances are polarized under the action of the electric field, resulting in an increase in dielectric loss. The higher the temperature, the faster the reaction rate, the more polar substances are generated, and the greater the dielectric loss.

[0083] S3. Obtain the terahertz time-domain spectra of insulating oils with different aging degrees at 120°C using the terahertz spectroscopy system, including the following S3.1) and S3.2).

[0084] S3.1) Build a transmission terahertz time-domain spectroscopy system.

[0085] To measure the terahertz absorption spectra of insulating oils with different aging degrees, a terahertz spectroscopy system for terahertz testing was built in this application, which is called a transmission terahertz time-domain spectroscopy system. Its principle is as Figure 3 shown, mainly including: a femtosecond laser, a beam splitter, a time delay device (delay line), a reflector, a terahertz emitter, a terahertz detector, a first parabolic mirror, a second parabolic mirror, a lock-in amplifier, and a PC control terminal. Among them, the femtosecond laser emits laser pulses, and the pump light and the probe light are obtained through the beam splitter. The pump light penetrates the insulating oil sample and reaches the terahertz detector together with the probe light passing through the time delay device (delay line) to obtain the terahertz time-domain spectrum. The time delay device is the delay line, which is located on the probe light path. The core function of the terahertz emitter is to generate terahertz pulses. The terahertz detector is used to receive the terahertz pulse time-domain signal after interacting with the insulating oil sample.

[0086] Figure 3In the specific embodiment shown, the beam splitter is located on the outgoing optical path of the femtosecond laser; the laser pulse emitted by the femtosecond laser is split into pump light and probe light by the beam splitter. The terahertz emitter is located on the reflected optical path of the beam splitter; the pump light reflected by the beam splitter is incident on the terahertz emitter, and terahertz pulses are generated by the terahertz emitter. The first parabolic mirror is located on the outgoing optical path of the terahertz emitter, and is used to focus the terahertz pulses generated by the terahertz emitter onto the surface of the insulating oil sample. The second parabolic mirror is located on the transmission optical path of the insulating oil sample, and is used to re-collect and focus the terahertz pulses transmitted through the insulating oil onto the terahertz detector.

[0087] The two parabolic mirrors are used to focus the terahertz wave onto the sample surface, and to re-collect and focus the terahertz wave transmitted through the sample onto the terahertz detector. This focusing and collection function is crucial for improving the spectral resolution and signal intensity of the system. Compared with lenses, parabolic mirrors have no dispersion, so they can focus the terahertz wave smaller, thereby improving the spatial resolution of the system.

[0088] Further as Figure 3 shown, the time delay device (delay line) is located on the transmitted optical path of the beam splitter. The probe light transmitted by the beam splitter passes through the time delay device (delay line) and then is incident on the reflector, and is reflected by the reflector onto the terahertz detector. The terahertz detector is connected to the PC control terminal via a lock-in amplifier. The PC control terminal is used to generate the terahertz time-domain spectrum of the insulating oil according to the terahertz pulse signal and the probe light signal received by the terahertz detector.

[0089] Among them, the lock-in amplifier is used in the terahertz time-domain spectroscopy system to improve the signal-to-noise ratio of the detection signal. It can phase-lock the detected weak terahertz pulse signal with the probe light signal, thereby effectively suppressing noise and improving the detectability of the signal. Through the lock-in amplification technology, the system can achieve high-precision time delay measurement, which is crucial for obtaining the time-domain waveform of the terahertz pulse. This high-precision measurement enables the system to accurately obtain the frequency-domain spectrum of the sample through Fourier transform. The lock-in amplifier can also significantly improve the dynamic range of the system, enabling the system to measure in a wider signal intensity range, so as to adapt to the characteristics of different samples.

[0090] S3.2) Time-domain signal analysis.

[0091] Figure 4 The terahertz time-domain spectra of insulating oils with different aging degrees at 120 °C obtained by experiments, where the abscissa is time and the ordinate is the time-domain signal. From Figure 4As can be seen from the results shown, as the aging time increases, the peak-to-peak value of the time-domain signal gradually decreases. As the aging time increases, the content of polar substances in the insulating oil increases, and the absorption of terahertz waves by the sample also gradually increases, resulting in a decrease in the transmission intensity, and thus the peak-to-peak value of the sample signal decreases. Based on the repeatability and reliability of the experimental data, it can be believed that the change in the main peak of the time-domain signal is not caused by experimental errors.

[0092] S4. Convert the time-domain spectrum to the frequency-domain spectrum and calculate the absorption coefficient and refractive index.

[0093] For subsequent data processing and analysis, the time-domain signal is transformed into a frequency-domain waveform by Fourier transform, as Figure 5 shown. The abscissa is the frequency, and the ordinate is the frequency-domain amplitude. As Figure 5 can be seen, as the aging time increases, the change in the terahertz frequency-domain amplitude signal of insulating oils with different aging degrees is not obvious, but a significant characteristic peak appears at 0.5 THz. However, considering that the reference signal also shows a characteristic peak at this position and the change is not obvious compared with insulating oils of different aging degrees, this characteristic peak cannot be selected as the characteristic parameter for the aging degree of insulating oil.

[0094] Figure 5 The reference signal in refers to the signal obtained by measuring a standard reference sample with known properties (such as air or a certain standard material) in terahertz time-domain spectroscopy. Its function is to provide a benchmark for calibrating and comparing the sample signal to eliminate the influence of systematic errors and environmental factors. The sample signal refers to the signal obtained by measuring the actual insulating oil sample in terahertz time-domain spectroscopy. These signals contain information about the physical and chemical properties of the insulating oil, such as absorption peaks, refractive index, etc., and can reflect the aging degree of the insulating oil.

[0095] Based on the frequency-domain amplitude and phase after Fourier transform of the sample signal and the reference signal, their refractive index and absorption coefficient can be calculated, as shown in the following formulas (1) and (2):

[0096]

[0097] Among them, is the phase at frequency ω, A(ω) is the frequency-domain amplitude at frequency ω. c is the propagation speed of terahertz waves in air; d is the thickness of the insulating oil sample. n s (ω) represents the real part of the refractive index at frequency ω; k(ω) represents the imaginary part of the refractive index at frequency ω, that is, the extinction coefficient. α(ω) is the terahertz absorption coefficient at frequency ω. Among them, ω usually refers to the angular frequency. refers to the phase difference between the reference signal and the sample signal.

[0098] According to the refractive index and absorption coefficient calculation results of formulas (1) and (2), the terahertz frequency-domain spectra of insulating oils with different aging degrees shown in Figure 6 are plotted. Figure 6 Part (a) of shows the variation of the refractive index with frequency. It can be seen that the refractive indices of all samples do not change much overall, only changing at the level of one-thousandth. Therefore, the refractive index is not used as a characteristic parameter for the aging degree of insulating oil. In addition, there is an obvious stratification phenomenon in the refractive index. In the low-frequency band, it increases with the increase of frequency, and in the high-frequency band, there is an obvious downward trend in some samples. Figure 6 Part (b) of shows the variation of the absorption coefficient with frequency. It can be seen that the overall change of the absorption coefficient is relatively regular, and regular characteristic absorption peaks appear at 2 THz and 2.3 THz. Moreover, as the aging time increases, the overall absorption coefficient increases. As the aging time increases, the content of polar substances in the insulating oil increases, and the absorption of the sample to terahertz waves also gradually increases, resulting in an overall increase in the absorption coefficient.

[0099] Furthermore, considering that the power-frequency dielectric loss is used to characterize the aging degree of insulating oil, and the power-frequency dielectric loss is affected by the overall content of polar substances, therefore, in this application, the integral value of the terahertz absorption coefficient is selected as the terahertz aging degree characteristic parameter, and its calculation formula is as follows:

[0100]

[0101] In the formula, ω1 is the lower frequency limit, with the unit of THz, which is 0.3 THz in this application; ω2 is the upper frequency limit, with the unit of THz, which is 2.5 THz in this application. α(ω) is the terahertz absorption coefficient at frequency ω, with the unit of cm -1 . S α is the integral value of the terahertz absorption coefficient, dimensionless.

[0102] S5. Establish a power-frequency dielectric loss model to evaluate the aging degree of insulating oil.

[0103] Calculate the S α of insulating oil samples with different aging degrees and the power-frequency dielectric loss, and draw a scatter plot as shown in Figure 7 . The abscissa is the integral value S α of the terahertz absorption coefficient, and the ordinate is the power-frequency dielectric loss. It can be seen from Figure 7 that as the terahertz characteristic parameter - the integral value S α of the terahertz absorption coefficient increases, the power-frequency dielectric loss also gradually increases. Calculate its Pearson correlation coefficient to be 0.985. The Pearson correlation coefficient represents the degree of linear correlation between two variables. Generally, when the Pearson correlation coefficient is greater than 0.8, it can be considered that there is a strong linear correlation between the two. Greater than zero indicates a positive correlation, and less than zero represents a negative correlation. Therefore, it can be considered that S αThere is a very strong linear positive correlation with the power frequency dielectric loss. Therefore, a linear fitting is performed on it, and the following linear model is obtained:

[0104] Tanδ = 0.08364S α +0.00818 (4)

[0105] In the formula, Tanδ is the measured power frequency dielectric loss, with the unit of %; S α is the integral value of the terahertz absorption coefficient, dimensionless. S α The fitting straight line of S and the power frequency dielectric loss is as Figure 8 shown. Its coefficient of determination R 2 is greater than 0.97, indicating that the fitting effect is good. Therefore, the linear model corresponding to this fitting straight line is used as the power frequency dielectric loss model of this application.

[0106] To verify the universality of this linear model, samples with a 130°C gradient aging degree are used as verification data. The terahertz time-domain spectra and absorption coefficients of the 130°C samples are obtained according to the above process, as shown in Figure 9 and Figure 10 shown respectively. It can be seen from Figure 9 that for insulating oil samples with different aging degrees at different aging temperatures, the peak-to-peak values of the terahertz time-domain signals also gradually decrease with the increase of the aging time. It can be seen from Figure 10 that the absorption coefficient gradually increases as a whole with the increase of the aging time. According to formula (3), calculate the terahertz characteristic parameter of the 130°C gradient aging degree sample - the integral value S of the terahertz absorption coefficient α , and substitute it into the established power frequency dielectric loss model (4) to verify its effectiveness. The results are as Figure 11 shown.

[0107] It can be seen from Figure 11 that all data points fall within the ±0.05% error band and the ±25% error band. The national standard GB / T 5654-2007 "Measurement of Relative Permittivity, Dielectric Dissipation Factor and DC Resistivity of Liquid Insulating Materials" requires that the measurement error of the power frequency dielectric loss of insulating oil is: the difference between the two measured tanδ values should not be greater than 0.0001 plus 25% of the larger of the two values. It can be seen that the power frequency dielectric loss model (4) established in this application not only meets the national standard detection accuracy, but also has a smaller error compared with the national standard at high power frequency dielectric loss data points. Therefore, the power frequency dielectric loss model (4) established in this application can effectively predict the power frequency dielectric loss of samples with different aging degrees at 130°C, and then reflect the aging degree of insulating oil, with extremely high accuracy.

[0108] In summary, this application proves that there is a good linear relationship between the integral value of the terahertz absorption coefficient and the aging degree of insulating oil. Therefore, the aging degree of insulating oil can be judged according to the fitting model (4) combined with the terahertz test results, realizing real-time, rapid and non-destructive evaluation of the aging degree of insulating oil. The specific non-destructive detection method for the aging degree of insulating oil is as described in Steps 1 to 5 below.

[0109] Step 1: In-situ windowing is performed on the oil-immersed transformer, and terahertz testing is carried out on the insulating oil flowing through the window to obtain the terahertz time-domain spectrum.

[0110] Based on the power frequency dielectric loss model (4) established in this application, real-time and in-situ online detection of the insulating oil in the transformer can be achieved. Specifically, for the monitored oil-immersed transformer, a window is directly opened on the transformer to allow the insulating oil of the operating transformer to flow through this window, and terahertz testing is carried out on the insulating oil flowing through the window. This method is equivalent to sampling during the test, except that the sampling process is in-situ (at the window opening), non-destructive, and real-time monitoring can be achieved.

[0111] Use Figure 3 the shown transmission terahertz time-domain spectroscopy system to perform terahertz testing on the insulating oil flowing through the window to obtain the terahertz time-domain spectrum; the abscissa of the terahertz time-domain spectrum is time, and the ordinate is the time-domain signal. It should be noted that when directly performing terahertz testing on the insulating oil in the transformer, the position of the parabolic mirror needs to be adjusted to ensure Figure 3 the terahertz pulse emitted by the terahertz emitter (corresponding to the pump light) in

[0112] can enter the insulating oil at the window, and the terahertz pulse transmitted through the insulating oil can be collected again and focused on the terahertz detector, so as to obtain the real-time terahertz time-domain spectrum.

[0113] The terahertz time-domain spectrum is converted into a terahertz frequency-domain spectrum by Fourier transform; the abscissa of the terahertz frequency-domain waveform is frequency, and the ordinate is the frequency-domain amplitude.

[0114] According to the frequency-domain amplitude of the terahertz frequency-domain waveform, the terahertz absorption coefficient α(ω) at frequency ω can be calculated using the above formula (2).

[0115] Step 3: Calculate the integral value of the terahertz absorption coefficient according to the terahertz absorption coefficient.

[0116] According to the terahertz absorption coefficient α(ω) at frequency ω, the integral value S of the terahertz absorption coefficient can be calculated using formula (3) α .

[0117] Step 4: Substitute the integrated value of the terahertz absorption coefficient into the power frequency dielectric loss model to calculate the current power frequency dielectric loss.

[0118] The determination process of the power frequency dielectric loss model of the insulating oil in this application is as described in S1 to S5 above. Substitute the integrated value S of the terahertz absorption coefficient currently detected α into the power frequency dielectric loss model (4), and the current power frequency dielectric loss Tanδ can be calculated.

[0119] Step 5: Determine the aging degree of the insulating oil according to the current power frequency dielectric loss.

[0120] This application represents the aging state of the insulating oil by its dielectric loss. That is to say, the larger the current power frequency dielectric loss Tanδ, the higher the aging degree of the current insulating oil.

[0121] Currently, the process of directly testing the dielectric loss relies on cumbersome sample processing and a slow testing process. In this application, by performing real-time terahertz testing on the insulating oil in the transformer and then calculating, the power frequency dielectric loss can be obtained without cumbersome sample processing and a slow testing process. Therefore, the operation is more convenient and the detection efficiency is higher. Moreover, the transmission terahertz time-domain spectroscopy system used in this application can perform non-contact, non-destructive real-time in-situ detection on the insulating oil, which is efficient and fast. Terahertz characteristic parameter of 120°C gradient aging sample - integrated value S of terahertz absorption coefficient α has a linear positive correlation with the aging degree of the insulating oil. The Pearson correlation coefficient is greater than 0.985, and the goodness of fit of the established linear model is greater than 0.97. The effectiveness of this linear model was verified using 130°C gradient aging samples. All samples fall within the ±0.05% error band, indicating that the power frequency dielectric loss model (4) can effectively evaluate the aging degree of the insulating oil, and the error is smaller compared to the national standard at high power frequency dielectric loss data points, and the detection accuracy is higher.

[0122] In an exemplary embodiment, the present application further provides a computer device, which may be a server or a terminal. The computer device includes a processor, a memory, an input / output interface, and a communication interface. Among them, the processor, the memory, and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The input / output interface of the computer device is used to exchange information between the processor and external devices. The communication interface of the computer device is used to communicate with external terminals through a network connection. When the computer program is executed by the processor, it implements the non-destructive detection method for the aging degree of insulating oil, specifically including: obtaining the terahertz time-domain spectrum of the insulating oil in the oil-immersed transformer; using Fourier transform to convert the terahertz time-domain spectrum into a terahertz frequency-domain spectrum, and calculating the terahertz absorption coefficient using formula (2); according to the terahertz absorption coefficient, calculating the integral value of the terahertz absorption coefficient using formula (3); substituting the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model (4) to calculate the current power-frequency dielectric loss; and determining the aging degree of the insulating oil according to the current power-frequency dielectric loss.

[0123] In an exemplary embodiment, the present application further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements the non-destructive detection method for the aging degree of insulating oil, specifically including: obtaining the terahertz time-domain spectrum of the insulating oil in the oil-immersed transformer; using Fourier transform to convert the terahertz time-domain spectrum into a terahertz frequency-domain spectrum, and calculating the terahertz absorption coefficient using formula (2); according to the terahertz absorption coefficient, calculating the integral value of the terahertz absorption coefficient using formula (3); substituting the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model (4) to calculate the current power-frequency dielectric loss; and determining the aging degree of the insulating oil according to the current power-frequency dielectric loss.

[0124] In an exemplary embodiment, the present application further provides a computer program product, including a computer program. When the computer program is executed by a processor, it implements the non-destructive detection method for the aging degree of insulating oil, specifically including: obtaining the terahertz time-domain spectrum of the insulating oil in the oil-immersed transformer; using Fourier transform to convert the terahertz time-domain spectrum into a terahertz frequency-domain spectrum, and calculating the terahertz absorption coefficient using formula (2); according to the terahertz absorption coefficient, calculating the integral value of the terahertz absorption coefficient using formula (3); substituting the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model (4) to calculate the current power-frequency dielectric loss; and determining the aging degree of the insulating oil according to the current power-frequency dielectric loss.

[0125] Those of ordinary skill in the art can understand that all or part of the processes in the above-described embodiment methods can be completed by hardware related to computer program instructions. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiment methods as described above. Among them, any reference to a memory or other medium provided in the various embodiments of the present application can include at least one of non-volatile and volatile memories. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0126] It should be noted that the information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the present application are all information and data authorized by the user or fully authorized by all parties, and the collection, use, and processing of the relevant data need to comply with the relevant regulations.

[0127] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0128] In this article, specific examples are used to elaborate on the principles and implementation manners of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A non-destructive testing method for the aging degree of insulating oil, characterized in that, Including: Performing in-situ windowing on an oil-immersed transformer, conducting terahertz testing on the insulating oil flowing through the window, and obtaining a terahertz time-domain spectrum; Converting the terahertz time-domain spectrum to a terahertz frequency-domain spectrum by Fourier transform and calculating the terahertz absorption coefficient; Calculating the integral value of the terahertz absorption coefficient based on the terahertz absorption coefficient; Substituting the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model to calculate the current power-frequency dielectric loss; Determining the aging degree of the insulating oil based on the current power-frequency dielectric loss.

2. The non-destructive testing method for the aging degree of insulating oil according to claim 1, wherein The conducting terahertz testing on the insulating oil flowing through the window and obtaining the terahertz time-domain spectrum specifically includes: Using a transmission terahertz time-domain spectroscopy system to conduct terahertz testing on the insulating oil flowing through the window and obtaining the terahertz time-domain spectrum; the abscissa of the terahertz time-domain spectrum is time, and the ordinate is the time-domain signal.

3. The non-destructive testing method for the aging degree of insulating oil according to claim 2, characterized in that The transmission terahertz time-domain spectroscopy system includes: a femtosecond laser, a beam splitter, a time-delay device, a reflector, a terahertz emitter, a terahertz detector, a first parabolic mirror, a second parabolic mirror, a lock-in amplifier, and a PC control terminal; The beam splitter is located on the output optical path of the femtosecond laser; the laser pulse emitted by the femtosecond laser is divided into a pump light and a probe light by the beam splitter; The terahertz emitter is located on the reflected optical path of the beam splitter; the pump light reflected by the beam splitter is incident on the terahertz emitter, and a terahertz pulse is generated by the terahertz emitter; The first parabolic mirror is located on the output optical path of the terahertz emitter and is used to focus the terahertz pulse generated by the terahertz emitter onto the window of the oil-immersed transformer; The second parabolic mirror is located on the transmission optical path of the insulating oil at the window and is used to re-collect and focus the terahertz pulse transmitted through the insulating oil onto the terahertz detector; The time-delay device is located on the transmission optical path of the beam splitter; the probe light transmitted by the beam splitter passes through the time-delay device and then is incident on the reflector, and is reflected by the reflector to the terahertz detector; The terahertz detector is connected to the PC control terminal via a lock-in amplifier; the PC control terminal is used to generate the terahertz time-domain spectrum of the insulating oil according to the terahertz pulse signal and the probe light signal received by the terahertz detector.

4. The non-destructive testing method for the aging degree of insulating oil according to claim 2, wherein The converting the terahertz time-domain spectrum to a terahertz frequency-domain spectrum by Fourier transform and calculating the terahertz absorption coefficient specifically includes: Converting the terahertz time-domain spectrum to a terahertz frequency-domain waveform by Fourier transform; the abscissa of the terahertz frequency-domain waveform is frequency, and the ordinate is the frequency-domain amplitude; According to the frequency-domain amplitude of the terahertz frequency-domain waveform, the formula is used to calculate the terahertz absorption coefficient α(ω) at the frequency ω; where n s (ω) represents the real part of the refractive index at the frequency ω, k(ω) represents the imaginary part of the refractive index at the frequency ω; c is the propagation speed of the terahertz wave in air; d is the thickness of the insulating oil sample; A(ω) is the frequency-domain amplitude at the frequency ω.

5. The non-destructive detection method for the aging degree of insulating oil according to claim 4, wherein, The calculating the integral value of the terahertz absorption coefficient based on the terahertz absorption coefficient specifically includes: According to the terahertz absorption coefficient α(ω) at the frequency ω, the formula is used to calculate the integral value S of the terahertz absorption coefficient α ; where ω1 is the lower frequency limit; ω2 is the upper frequency limit.

6. The non-destructive testing method for the aging degree of insulating oil according to claim 5, characterized in that, The substituting the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model to calculate the current power-frequency dielectric loss specifically includes: Integrate the terahertz absorption coefficient value S α Substitute it into the power frequency dielectric loss model Tanδ = 0.08364S α + 0.00818 to calculate the current power frequency dielectric loss Tanδ.

7. The non-destructive detection method for the aging degree of insulating oil according to claim 6, characterized in that, The determining the aging degree of the insulating oil based on the current power-frequency dielectric loss specifically includes: The greater the current power-frequency dielectric loss Tanδ, the higher the determined aging degree of the current insulating oil.

8. A computer device, comprising: A memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that the processor executes the computer program to implement a non-destructive detection method for the aging degree of insulating oil; The non-destructive testing method for the aging degree of the insulating oil includes: Obtaining the terahertz time-domain spectrum of the insulating oil in the oil-immersed transformer; Converting the terahertz time-domain spectrum into a terahertz frequency-domain spectrum by Fourier transform and calculating the terahertz absorption coefficient; Calculating the integral value of the terahertz absorption coefficient according to the terahertz absorption coefficient; Substituting the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model to calculate the current power-frequency dielectric loss; Determining the aging degree of the insulating oil according to the current power-frequency dielectric loss.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements a non-destructive testing method for the aging degree of the insulating oil; The non-destructive testing method for the aging degree of the insulating oil includes: Obtaining the terahertz time-domain spectrum of the insulating oil in the oil-immersed transformer; Converting the terahertz time-domain spectrum into a terahertz frequency-domain spectrum by Fourier transform and calculating the terahertz absorption coefficient; Calculating the integral value of the terahertz absorption coefficient according to the terahertz absorption coefficient; Substituting the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model to calculate the current power-frequency dielectric loss; Determining the aging degree of the insulating oil according to the current power-frequency dielectric loss.

10. A computer program product comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements a non-destructive testing method for the aging degree of the insulating oil; The non-destructive testing method for the aging degree of the insulating oil includes: Obtaining the terahertz time-domain spectrum of the insulating oil in the oil-immersed transformer; Converting the terahertz time-domain spectrum into a terahertz frequency-domain spectrum by Fourier transform and calculating the terahertz absorption coefficient; Calculating the integral value of the terahertz absorption coefficient according to the terahertz absorption coefficient; Substituting the integral value of the terahertz absorption coefficient into the power-frequency dielectric loss model to calculate the current power-frequency dielectric loss; Determining the aging degree of the insulating oil according to the current power-frequency dielectric loss.

Images