Terahertz-based method for determining functional characteristic parameters of mineral insulating oil

Abstract

The invention discloses a method for determining functional characteristic parameters of mineral insulating oil based on terahertz, and relates to the technical field of insulating oil functional characteristic parameter detection.The method comprises the steps that a terahertz time-domain spectrum of an insulating oil degradation standard sample is obtained, characteristic parameters of the insulating oil degradation standard sample are extracted, and an insulating oil terahertz marked line is determined; determining the relationship between the moisture content and the breakdown voltage of the insulating oil degradation standard sample, and determining a breakdown voltage terahertz marked line based on the relationship between the moisture content and the breakdown voltage of the insulating oil degradation standard sample and the moisture terahertz marked line; obtaining a terahertz time-domain spectrum of the to-be-detected insulating oil, and extracting characteristic parameters of the to-be-detected insulating oil based on the terahertz time-domain spectrum; and based on the characteristic parameters of the to-be-detected insulating oil, the breakdown voltage terahertz marked line, the acid value terahertz marked line and the dielectric loss terahertz marked line, determining predicted values of the functional characteristic parameters of the to-be-detected insulating oil. According to the invention, the accuracy and convenience of functional characteristic parameter prediction of the to-be-tested insulating oil can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of insulating oil performance detection, and in particular to a method for determining functional characteristic parameters of mineral insulating oil based on terahertz. Background Art

[0002] Under the long-term operation conditions of electrical, thermal, and mechanical stress, the performance of the insulation material of oil-immersed power equipment gradually deteriorates, and the probability of failure increases year by year. The functional characteristics (breakdown voltage, dielectric loss, and acid value) of the insulating oil of oil-filled equipment can effectively reflect the operating risks of the equipment. According to DL / T596-2021 "Preventive Test Procedures for Power Equipment", the above indicators of each equipment must be evaluated at least once every 1 to 3 years.

[0003] The breakdown voltage of insulating oil is a measure of the ability of insulating oil to withstand voltage inside electrical equipment (also known as the dielectric strength of insulating oil) without being broken down. It is one of the main means of testing the performance of transformer oil. The voltage at which insulating oil breaks down under specified conditions is called the breakdown voltage of insulating oil. The unit is generally KV, which is actually the instantaneous breakdown voltage value of the insulating oil. The traditional measurement method - the boost method has complex test steps, requires professional equipment, high-voltage operation, and is dangerous, and the test results are highly dispersed.

[0004] The dielectric loss factor of insulating oil is an important indicator to measure the energy loss of insulating oil under the action of AC electric field. It reflects the dielectric performance of insulating oil under the action of electric field, that is, the loss characteristics of insulating oil. The smaller the value of dielectric loss factor, the better the insulation performance of insulating oil. The traditional measurement method, bridge method, is easily interfered by the outside world, and the test procedure is complicated, the automation level is low, the operation workload is large, and the human factors have a great influence. The accuracy of wattmeter method is low, the precision of resonant circuit method is not high, the measurement frequency is not fixed, and the measurement method is not standardized. The existing dielectric loss is mainly a full digital measurement method, which realizes the full digital filtering technology and vector method test principle through dielectric loss tester, and realizes detection through capacitor voltage division method. However, for different oil-filled equipment, the size of the equivalent test capacitor is different, and the boost mode of this variable frequency power supply is single. The dielectric loss measurement of test capacitors of different capacitance sizes has different accuracy and poor versatility.

[0005] The acid value of insulating oil indicates that the oil contains acidic substances, that is, the total value of organic acids and inorganic acids. It is generally expressed by the number of mg of potassium hydroxide required to neutralize 1g of acidic substances in insulating oil. Various acidic substances in insulating oil will increase the conductivity of the oil, reduce the insulation performance of the oil, and may also cause corrosion to metals. Under high operating temperatures (above 80°C), solid fiber paper insulation materials will age, thereby shortening the service life of the equipment. The traditional measurement method - neutralization titration is easily affected by external interference, and the test procedure is complex, the automation level is low, the operation workload is large, and the human factor has a great influence. Summary of the invention

[0006] The purpose of the present application is to provide a method for determining functional characteristic parameters of mineral insulating oil based on terahertz, so as to solve the problems of low accuracy and complex operation in determining the functional characteristic parameters of mineral insulating oil.

[0007] To achieve the above objectives, this application provides the following solutions:

[0008] The present application provides a method for determining functional characteristic parameters of mineral insulating oil based on terahertz, and the method for determining functional characteristic parameters of mineral insulating oil based on terahertz includes:

[0009] preparing insulating oil degradation standard samples and obtaining terahertz time-domain spectra of the insulating oil degradation standard samples;

[0010] Extracting characteristic parameters of the insulating oil deterioration standard sample based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample; the characteristic parameters include moisture characteristic parameters, acid value characteristic parameters and dielectric loss characteristic parameters;

[0011] Determine the insulating oil terahertz marking line based on the characteristic parameters of the insulating oil degradation standard sample; the insulating oil terahertz marking line includes a moisture terahertz marking line, an acid value terahertz marking line and a dielectric loss terahertz marking line;

[0012] Determine the relationship between the moisture content and the breakdown voltage of the insulating oil deterioration standard sample, and determine the breakdown voltage terahertz calibration line based on the relationship between the moisture content and the breakdown voltage of the insulating oil deterioration standard sample and the insulating oil moisture terahertz calibration line;

[0013] Acquire a terahertz time-domain spectrum of the insulating oil to be tested, and extract characteristic parameters of the insulating oil to be tested based on the terahertz time-domain spectrum of the insulating oil to be tested;

[0014] Based on the characteristic parameters of the insulating oil to be tested, the breakdown voltage terahertz line, the acid value terahertz line and the dielectric loss terahertz line, the predicted values ​​of the functional characteristic parameters of the insulating oil to be tested are determined; the functional characteristic parameters include the breakdown voltage, the acid value and the dielectric loss.

[0015] Optionally, obtaining a terahertz time domain spectrum of an insulating oil degradation standard sample specifically includes:

[0016] Select a polystyrene standard cuvette with a set optical path as the sample cell, and use the corresponding empty cuvette as the reference sample cell;

[0017] Under a set temperature and set humidity environment, a transmission terahertz spectrometer is used to irradiate the insulating oil degradation standard sample contained in the sample pool and the reference sample pool, respectively, to obtain a terahertz time-domain spectrum of the insulating oil degradation standard sample and a corresponding reference terahertz time-domain spectrum.

[0018] Optionally, extracting characteristic parameters of the insulating oil degradation standard sample based on the terahertz time-domain spectrum of the insulating oil degradation standard sample specifically includes:

[0019] Determine the refractive index of the insulating oil deterioration standard sample based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample, and plot the terahertz refraction spectrum of the insulating oil deterioration standard sample based on the refractive index of the insulating oil deterioration standard sample;

[0020] Determine the absorption coefficient of the insulating oil deterioration standard sample based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample and the refractive index of the insulating oil deterioration standard sample, and plot the terahertz absorption spectrum of the insulating oil deterioration standard sample based on the absorption coefficient of the insulating oil deterioration standard sample;

[0021] Determine the dielectric loss of the insulating oil deterioration standard sample based on the refractive index of the insulating oil deterioration standard sample and the extinction coefficient of the insulating oil deterioration standard sample, and draw a terahertz dielectric loss spectrum of the insulating oil deterioration standard sample based on the dielectric loss of the insulating oil deterioration standard sample; the extinction coefficient is obtained based on the terahertz time domain spectrum of the insulating oil deterioration standard sample and the refractive index of the insulating oil deterioration standard sample;

[0022] Based on terahertz refraction spectrum and terahertz dielectric loss spectrum, the moisture characteristic parameters of insulating oil degradation standard samples are extracted;

[0023] Based on terahertz absorption spectroscopy, the acid value characteristic parameters of insulating oil deterioration standard samples are extracted;

[0024] Based on the terahertz dielectric loss spectrum, the dielectric loss characteristic parameters of the insulating oil degradation standard sample are extracted.

[0025] Optionally, determining the refractive index of the insulating oil deterioration standard sample based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample specifically includes:

[0026] Based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample, a terahertz frequency-domain spectrum of the insulating oil deterioration standard sample is obtained, and a frequency-domain phase of the terahertz frequency-domain spectrum of the insulating oil deterioration standard sample is determined;

[0027] Based on the reference terahertz time-domain spectrum, determining a reference terahertz frequency-domain spectrum, and determining a frequency-domain phase of the reference terahertz frequency-domain spectrum;

[0028] The refractive index of the insulating oil deterioration standard sample is determined based on the frequency domain phase of the terahertz frequency domain spectrum of the insulating oil deterioration standard sample and the frequency domain phase of the reference terahertz frequency domain spectrum.

[0029] Optionally, determining the absorption coefficient of the insulating oil deterioration standard sample based on the terahertz time domain spectrum of the insulating oil deterioration standard sample and the refractive index of the insulating oil deterioration standard sample specifically includes:

[0030] Based on the terahertz frequency domain spectrum of the insulating oil degradation standard sample, the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil degradation standard sample is determined;

[0031] Based on the reference terahertz frequency domain spectrum, determining the frequency domain amplitude of the reference terahertz frequency domain spectrum;

[0032] Determine the extinction coefficient of the insulating oil deterioration standard sample based on the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil deterioration standard sample, the frequency domain amplitude of the reference terahertz frequency domain spectrum, and the refractive index of the insulating oil deterioration standard sample;

[0033] Based on the extinction coefficient of the insulating oil deterioration standard sample, the absorption coefficient of the insulating oil deterioration standard sample is determined.

[0034] Alternatively, the expression for the extinction coefficient of the insulating oil degradation standard is:

[0035]

[0036] Wherein, κ(ω) is the extinction coefficient of the insulating oil deterioration standard sample; c is the speed of light in a vacuum; d is the thickness of the insulating oil deterioration standard sample; ω is the angular frequency; n is the refractive index of the insulating oil deterioration standard sample; A s (ω) is the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil degradation standard sample; A r (ω) is the frequency domain amplitude of the reference terahertz frequency domain spectrum;

[0037] The expression of the absorption coefficient of the insulating oil degradation standard is:

[0038] α(ω)=2κ(ω)ω / c;

[0039] Where α(ω) is the absorption coefficient of the insulating oil degradation standard.

[0040] Optionally, determining the dielectric loss of the insulating oil deterioration standard sample based on the refractive index of the insulating oil deterioration standard sample and the extinction coefficient of the insulating oil deterioration standard sample specifically includes:

[0041] Based on the refractive index and extinction coefficient of the insulating oil deterioration standard sample, the real part of the dielectric constant and the imaginary part of the dielectric constant of the insulating oil deterioration standard sample are determined;

[0042] The dielectric loss of the insulating oil deterioration standard sample is determined based on the real part of the dielectric constant and the imaginary part of the dielectric constant of the insulating oil deterioration standard sample.

[0043] Optionally, the real part of the dielectric constant D of the insulating oil degradation standard sample r The expression is:

[0044] D r (ω)=n(ω) 2 -κ(ω) 2 ;

[0045] Imaginary part D of dielectric constant of insulating oil deterioration standard sample i The expression is:

[0046] D i (ω) = 2n(ω)κ(ω);

[0047] Dielectric loss D of insulating oil deterioration standard sample T The expression is:

[0048]

[0049] Optionally, determining the insulating oil terahertz marking line based on the characteristic parameters of the insulating oil degradation standard sample specifically includes:

[0050] The dielectric loss, acid value and moisture content of the insulating oil deterioration standard sample are measured respectively to obtain the dielectric loss measurement value, acid value measurement value and moisture measurement value of the insulating oil deterioration standard sample;

[0051] The relationship between the moisture characteristic parameters of the insulating oil degradation standard sample and the moisture measurement value is fitted to obtain the moisture terahertz calibration line;

[0052] The relationship between the acid value characteristic parameters of the insulating oil degradation standard sample and the acid value measurement value is fitted to obtain the acid value terahertz calibration line;

[0053] The relationship between the dielectric loss characteristic parameters of the insulating oil degradation standard sample and the dielectric loss measurement value is fitted to obtain the dielectric loss terahertz calibration line.

[0054] Optionally, the expression for the relationship between the moisture content of the insulating oil deterioration standard sample and the breakdown voltage is:

[0055]

[0056] Among them, Breakdown represents the breakdown voltage; e represents the natural constant; Oilwater represents the water content of the insulating oil;

[0057] The expression of the terahertz line of the breakdown voltage of insulating oil is:

[0058]

[0059] Wherein, Breakdown represents the breakdown voltage; It represents the average refractive index in the low frequency band of the terahertz refraction spectrum; Indicates the average value of dielectric loss in the low frequency band of the terahertz dielectric loss spectrum; ΔPeak 1.7T The refractive index change value of 1.7THz band relative to the low frequency band in the terahertz refraction spectrum;

[0060] The expression of the dielectric loss terahertz line of insulating oil is:

[0061] tanδ . =-29.46733+1479.23534D Ta ;

[0062] Wherein, tanδ represents the power frequency dielectric loss; D Ta Indicates dielectric loss characteristic parameter;

[0063] The expression of the acid value terahertz line is:

[0064] acide=-0.80625+2.5795P 2.1THz ;

[0065] Wherein, acidide represents acid value; P 2.1THz Represents the characteristic parameter of acid value.

[0066] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0067] The present application discloses a method for determining functional characteristic parameters of mineral insulating oil based on terahertz. Based on the terahertz time-domain spectrum of a deteriorated insulating oil standard sample, a terahertz calibration line of the breakdown voltage, a terahertz calibration line of the acid value and a terahertz calibration line of the dielectric loss of the insulating oil are obtained. Then, based on the terahertz time-domain spectrum of the insulating oil to be tested, characteristic parameters of the insulating oil to be tested are extracted. In combination with the terahertz calibration line of the insulating oil, a predicted value of the breakdown voltage, a predicted value of the acid value and a predicted value of the dielectric loss of the insulating oil to be tested are determined. That is, only the terahertz time-domain spectrum of the insulating oil to be tested needs to be obtained and the terahertz calibration line of the insulating oil is determined, so that the non-destructive prediction of the breakdown voltage, the acid value and the dielectric loss of the insulating oil to be tested can be achieved, which not only improves the accuracy of the prediction of the functional characteristic parameters of the insulating oil to be tested, but also improves the convenience of the prediction of the functional characteristic parameters of the insulating oil to be tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0069] Figure 1 It is a flow chart of a method for determining functional characteristic parameters of mineral insulating oil based on terahertz in one embodiment of the present application;

[0070] Figure 2 A schematic diagram of the structure of a transmission terahertz spectrometer and a test process of a terahertz time-domain spectrum of an insulating oil degradation standard sample provided in an embodiment of the present application;

[0071] Figure 3 A schematic diagram of a terahertz time-domain spectrum of an insulating oil degradation standard sample and a reference terahertz time-domain spectrum provided in an embodiment of the present application;

[0072] Figure 4 A schematic diagram of amplifying the signal peak of a terahertz time-domain spectrum of an insulating oil degradation standard sample provided in one embodiment of the present application;

[0073] Figure 5 A schematic diagram of a terahertz refraction spectrum of a standard sample of insulating oil degradation provided in one embodiment of the present application;

[0074] Figure 6 A schematic diagram of a terahertz absorption spectrum of a standard sample of insulating oil degradation provided in one embodiment of the present application;

[0075] Figure 7 A schematic diagram of a terahertz dielectric loss spectrum of a standard sample of insulating oil degradation provided in one embodiment of the present application;

[0076] Figure 8 A schematic diagram of a terahertz absorption spectrum after baseline correction provided in one embodiment of the present application;

[0077] Fig. 9 A schematic diagram of a terahertz dielectric loss spectrum after baseline correction provided in an embodiment of the present application;

[0078] Fig.10 A schematic diagram of the fitting results of the relationship between the acid value characteristic parameters of the insulating oil degradation standard sample provided in one embodiment of the present application and the acid value measurement value obtained by the national standard test;

[0079] Fig.11 A schematic diagram of the fitting results of the relationship between the dielectric loss characteristic parameters of the insulating oil degradation standard sample provided in one embodiment of the present application and the dielectric loss measurement value obtained by the national standard test;

[0080] Fig.12 A schematic diagram of a curve showing the relationship between moisture and breakdown voltage provided in an embodiment of the present application. DETAILED DESCRIPTION

[0081] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0082] Terahertz time-domain spectroscopy (THz-TDS) shows great potential in the field of nondestructive testing of oil-paper insulation aging. The energy of terahertz waves is equivalent to the energy of polar molecular vibration, and its spectrum carries rich material fingerprint information. As a spectral testing technology that has emerged in recent years, THz-TDS has been successfully applied to some material detection and identification occasions as a supplement to traditional spectral technology. Substances such as acid, furfural and water produced by the deterioration of oil-paper insulation are polar molecules, which will cause increased dielectric loss, increased acid value and reduced breakdown voltage. Terahertz is sensitive to polar substances, so the performance of insulating oil breakdown voltage, dielectric loss and acid value can be nondestructively tested based on terahertz.

[0083] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0084] In an exemplary embodiment, Figure 1 As shown, a method for determining the functional characteristic parameters of mineral insulating oil based on terahertz is provided, comprising the following steps S1 to S6. Among them:

[0085] Step S1, preparing an insulating oil degradation standard sample, and obtaining a terahertz time-domain spectrum of the insulating oil degradation standard sample.

[0086] Step S2, extracting characteristic parameters of the insulating oil deterioration standard sample based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample; the characteristic parameters include moisture characteristic parameters, acid value characteristic parameters and dielectric loss characteristic parameters.

[0087] Step S3, determining the insulating oil terahertz marking line based on the characteristic parameters of the insulating oil degradation standard sample; the insulating oil terahertz marking line includes a moisture terahertz marking line, an acid value terahertz marking line and a dielectric loss terahertz marking line.

[0088] Step S4, determining the relationship between the moisture content and the breakdown voltage of the insulating oil deterioration standard sample, and determining the breakdown voltage terahertz calibration line based on the relationship between the moisture content and the breakdown voltage of the insulating oil deterioration standard sample and the insulating oil moisture terahertz calibration line.

[0089] Step S5, obtaining a terahertz time-domain spectrum of the insulating oil to be tested, and extracting characteristic parameters of the insulating oil to be tested based on the terahertz time-domain spectrum of the insulating oil to be tested.

[0090] Step S6, determining predicted values ​​of functional characteristic parameters of the insulating oil to be tested based on characteristic parameters of the insulating oil to be tested, breakdown voltage terahertz line, acid value terahertz line and dielectric loss terahertz line; the functional characteristic parameters include breakdown voltage, acid value and dielectric loss.

[0091] As an optional implementation, in step S1, when preparing the insulating oil degradation standard sample, a gradient accelerated thermal aging experiment is used to prepare insulating oils with different dielectric loss values, and on-site transformer insulating oils of the same manufacturer with different operating years can also be used as degradation standards.

[0092] Aging can cause the oil or fiber to decompose, forming various polar products that dissolve in the oil, resulting in an increase in its acid value, increased dielectric loss, and reduced breakdown voltage. The insulating oil degradation standard sample was prepared by gradient accelerated thermal aging experiment. Karamay #25 mineral oil and sulfate cellulose insulating paper (0.12mm thick) were selected. The oil and paper were vacuum dried at 90℃ / 50Pa for 48h, and then the paper was immersed in insulating oil and vacuum immersed at 60℃ / 50Pa for 24h. After that, the oil and paper were taken out and divided into glass bottles with an oil-paper ratio of 10:1 (1L oil + 87g paper) and sealed to prepare the first batch of samples. The prepared first batch of samples were placed in a 130℃ aging box for gradient accelerated thermal aging experiment. The whole aging experiment lasted for 128 days, and sampling was performed at intervals. Part of the insulating oil was taken from each sample in a headspace gas phase bottle with strong airtightness, which was sealed and stored at a constant temperature of 4℃ to prevent the volatilization of polar substances in the oil, slow down the degradation rate of the insulating oil, prevent the reaction of internal substances, and ensure that the samples sampled before and after will not change. After all the sampling was completed, the insulating oil degradation standard sample was obtained, and finally the terahertz test was carried out uniformly.

[0093] As an optional implementation, in step S1, obtaining the terahertz time domain spectrum of the insulating oil degradation standard sample specifically includes:

[0094] Step S11, select a polystyrene standard cuvette with a set optical path as a sample cell, and use a corresponding empty cuvette as a reference sample cell. Specifically, select a polystyrene standard cuvette with a set optical path (capacity of 4.5 mL) with a 10 mm optical path.

[0095] Step S12, under a set temperature and set humidity environment, using a transmission terahertz spectrometer to irradiate the insulating oil degradation standard sample contained in the sample pool and the reference sample pool respectively, to obtain a terahertz time-domain spectrum of the insulating oil degradation standard sample and a corresponding reference terahertz time-domain spectrum.

[0096] Specifically, at 25°C and 5% humidity, the terahertz time-domain spectrum of the insulating oil degradation standard sample was tested. Two samples were taken for each sample, and the average value of 256 tests was taken for each sample (taking about 2 minutes). The structure of the transmission terahertz spectrometer and the schematic diagram of the test process of the terahertz time-domain spectrum of the insulating oil degradation standard sample are shown in the figure. Figure 2 As shown, it includes two parts: the main unit and the sample stage. The specific test process is as follows: the built-in femtosecond laser of the transmission terahertz spectrometer outputs femtosecond pulses, which are divided into pump light and detection light by a beam splitter. The detection light passes through a time delay device and a reflector and enters the terahertz receiving end. The pump light is transmitted to the terahertz transmitting end to generate terahertz waves and penetrates the sample pool containing the insulating oil degradation standard sample to reach the terahertz receiving end, and the terahertz time-domain spectrum of the insulating oil degradation standard sample can be collected and obtained; at the same time, the terahertz time-domain spectrum signal of the empty cuvette is tested under the same conditions as a reference signal (i.e., the reference terahertz time-domain spectrum). Among them, the schematic diagram of the terahertz time-domain spectrum of the insulating oil degradation standard sample and the reference terahertz time-domain spectrum is shown in the figure below. Figure 3 As shown in the figure, the signal peak magnification diagram of the terahertz time domain spectrum of the insulating oil degradation standard sample is as follows Figure 4 shown.

[0097] As an optional implementation, step S2 specifically includes:

[0098] Step S21, based on the terahertz time domain spectrum of the insulating oil deterioration standard sample, determine the refractive index of the insulating oil deterioration standard sample, and draw the terahertz refraction spectrum of the insulating oil deterioration standard sample based on the refractive index of the insulating oil deterioration standard sample. The terahertz refraction spectrum of the insulating oil deterioration standard sample is as follows: Figure 5 shown.

[0099] Step S22, determining the absorption coefficient of the insulating oil deterioration standard sample based on the terahertz time domain spectrum of the insulating oil deterioration standard sample and the refractive index of the insulating oil deterioration standard sample, and plotting the terahertz absorption spectrum of the insulating oil deterioration standard sample based on the absorption coefficient of the insulating oil deterioration standard sample. The terahertz absorption spectrum of the insulating oil deterioration standard sample is as follows: Figure 6 shown.

[0100] Step S23, determining the dielectric loss of the insulating oil deterioration standard sample based on the refractive index of the insulating oil deterioration standard sample and the extinction coefficient of the insulating oil deterioration standard sample, and plotting the terahertz dielectric loss spectrum of the insulating oil deterioration standard sample based on the dielectric loss of the insulating oil deterioration standard sample; the extinction coefficient is obtained based on the terahertz time domain spectrum of the insulating oil deterioration standard sample and the refractive index of the insulating oil deterioration standard sample. The terahertz dielectric loss spectrum of the insulating oil deterioration standard sample is as follows: Figure 7 shown.

[0101] Step S24, extracting characteristic parameters of moisture in the insulating oil degradation standard sample based on the terahertz refraction spectrum and the terahertz dielectric loss spectrum.

[0102] Among them, the breakdown voltage is inverted from the moisture content, so the moisture content of the insulating oil deterioration standard sample is evaluated first. For the insulating oil, as the aging time increases, its dielectric loss and refractive index both increase, but as the moisture content increases, its dielectric loss increases (the polar substance (water) increases), and the refractive index decreases (the refractive index of water is lower than that of oil), that is, the refractive index includes the influence of both moisture and aging factors, and the influence of aging factors can be characterized by dielectric loss. Therefore, the moisture content relationship can be obtained by eliminating the influence of aging in the refraction spectrum.

[0103] At the same time, considering that the test process includes the propagation of terahertz waves in the air, it is necessary to remove the influence of air moisture, and the change value of the refractive index at 1.7THz of water terahertz is expressed as ΔPeak1.7T:

[0104] Oilwater=A+B×n+C×tanδ THz +D×ΔPeak 1.7T (1)

[0105] Among them, A, B, C, and D all represent coefficients; n is the refractive index of the insulating oil degradation standard sample, and the average value of 0.3-1THz is used as the input of the refractive index, tanδ THz is the stable dielectric loss mean value of the dielectric loss spectrum of insulating oil at 0.3-1THz, tanδ THz As dielectric loss input, ΔPeak 1.7T It is the refractive index change value of the 1.7THz band relative to the low-frequency band in the terahertz refraction spectrum, that is, the difference between the peak value of the refractive index of the deteriorated insulating oil standard at 1.7THz and the average refractive index of the low-frequency band.

[0106] Step S25, based on the terahertz absorption spectrum, extract the acid value characteristic parameter of the insulating oil deterioration standard sample. The acid value in the insulating oil is calculated by the number of milligrams of potassium hydroxide neutralized per gram, that is, the acid that produces the effect is the acid containing carboxyl, and the characteristic peak of acetic acid is 2.1THz, so the 2.1THz peak value P after baseline correction is selected. 2.1THzAcid value characteristic parameter as a standard sample of insulating oil deterioration.

[0107] Step S26, extracting dielectric loss characteristic parameters of the insulating oil degradation standard sample based on the terahertz dielectric loss spectrum.

[0108] As for dielectric loss, whether in the terahertz frequency band or at power frequency, the dielectric loss of insulating oil represents the loss caused by polar substances through various polarization types in a physical sense. Although there are large differences in the loss values ​​in different frequency bands, as the concentration of polar substances increases, the losses in each frequency band should show a similar growth law. In addition, various types of polar substances will respond in a very wide terahertz frequency band. Here, the average value DTa of the terahertz dielectric loss spectrum in the 0.5-1THz frequency band (the specific value range of the frequency band is determined by the signal-to-noise ratio of the instrument) is selected to study its relationship with the power frequency dielectric loss, as shown in formula (2).

[0109]

[0110] Where, f1 is the lower frequency limit, in THz, which is 0.5 THz in formula (2); f2 is the upper frequency limit, in THz, which is 1 THz in formula (2); N is the minimum 2 times the length of the THz time domain spectrum of the insulating oil degradation standard sample. k Number, dimensionless, 8192 in formula (2); F S is the instrument sampling frequency, in THz, which is 150 THz in formula (2).

[0111] As an optional implementation, in step S21, determining the refractive index of the insulating oil deterioration standard sample based on the terahertz time domain spectrum of the insulating oil deterioration standard sample specifically includes:

[0112] Step S211, based on the terahertz time domain spectrum of the insulating oil deterioration standard sample, obtain the terahertz frequency domain spectrum of the insulating oil deterioration standard sample, and determine the frequency domain phase of the terahertz frequency domain spectrum of the insulating oil deterioration standard sample; wherein, the calculation formula for converting the terahertz time domain spectrum of the insulating oil deterioration standard sample into the terahertz frequency domain spectrum is as follows:

[0113]

[0114] Among them, E s (ω) is the terahertz frequency domain spectrum signal of the insulating oil degradation standard sample; ω is the angular frequency; E s (t) is the terahertz time domain spectrum signal of the insulating oil degradation standard sample; A s (ω) is the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil degradation standard sample; φ s (ω) is the frequency domain phase of the terahertz frequency domain spectrum of the insulating oil degradation standard sample; i represents the imaginary unit.

[0115] Step S212, based on the reference terahertz time domain spectrum, determine the reference terahertz frequency domain spectrum, and determine the frequency domain phase of the reference terahertz frequency domain spectrum; wherein the calculation formula for converting the reference terahertz time domain spectrum into the reference terahertz frequency domain spectrum is as follows:

[0116]

[0117] Among them, E r (ω) is the reference terahertz time-domain spectroscopy signal, E r (t) is A r (ω) is the frequency domain amplitude of the reference terahertz spectrum, φ r (ω) is the frequency domain phase of the reference THz spectrum.

[0118] Step S213, determining the refractive index of the insulating oil deterioration standard sample based on the frequency domain phase of the terahertz frequency domain spectrum of the insulating oil deterioration standard sample and the frequency domain phase of the reference terahertz frequency domain spectrum. The calculation formula of the refractive index of the insulating oil deterioration standard sample is as follows:

[0119] n(ω)=1+[φ s (ω)-φ r (ω)]c / dω(5)

[0120] Among them, φ s (ω) is the frequency domain phase of the terahertz frequency domain spectrum of the insulating oil degradation standard; c is the speed of light in vacuum; d is the thickness of the sample.

[0121] As an optional implementation, in step S22, the absorption coefficient of the insulating oil deterioration standard sample is determined based on the terahertz time domain spectrum of the insulating oil deterioration standard sample and the refractive index of the insulating oil deterioration standard sample, specifically including:

[0122] Step S221 : determining the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil deterioration standard sample based on the terahertz frequency domain spectrum of the insulating oil deterioration standard sample.

[0123] Step S222: determining the frequency domain amplitude of the reference terahertz frequency domain spectrum based on the reference terahertz frequency domain spectrum.

[0124] Step S223, based on the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil deterioration standard sample, the frequency domain amplitude of the reference terahertz frequency domain spectrum and the refractive index of the insulating oil deterioration standard sample, determine the extinction coefficient of the insulating oil deterioration standard sample. The expression of the extinction coefficient of the insulating oil deterioration standard sample is:

[0125]

[0126] Wherein, κ(ω) is the extinction coefficient of the insulating oil deterioration standard sample; c is the speed of light in a vacuum; d is the thickness of the insulating oil deterioration standard sample; ω is the angular frequency; n(ω) is the refractive index of the insulating oil deterioration standard sample; A s (ω) is the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil degradation standard sample; A r (ω) is the frequency domain amplitude of the reference terahertz frequency domain spectrum;

[0127] Step S224, based on the extinction coefficient of the insulating oil deterioration standard sample, determine the absorption coefficient of the insulating oil deterioration standard sample. The expression of the absorption coefficient of the insulating oil deterioration standard sample is:

[0128] α(ω)=2κ(ω)ω / c (7)

[0129] Where α(ω) is the absorption coefficient of the insulating oil degradation standard.

[0130] As an optional implementation, in step S23, the dielectric loss of the insulating oil deterioration standard sample is determined based on the refractive index of the insulating oil deterioration standard sample and the extinction coefficient of the insulating oil deterioration standard sample, specifically including:

[0131] Step S231, based on the refractive index and extinction coefficient of the insulating oil deterioration standard sample, determine the real part of the dielectric constant and the imaginary part of the dielectric constant of the insulating oil deterioration standard sample; the real part of the dielectric constant D of the insulating oil deterioration standard sample r The expression is:

[0132] D r (ω)=n(ω) 2 -κ(ω) 2 (8)

[0133] Imaginary part D of dielectric constant of insulating oil deterioration standard sample i The expression is:

[0134] D i (ω)=2n(ω)κ(ω)(9)

[0135] Step S232, based on the real part of the dielectric constant and the imaginary part of the dielectric constant of the insulating oil deterioration standard sample, determine the dielectric loss of the insulating oil deterioration standard sample. T The expression is:

[0136]

[0137] Among them, the optical properties and dielectric properties of the dielectric can be described by Maxwell's equations. Ignoring the influence of the magnetic field, the relationship between the complex dielectric constant D* and the complex refractive index n* is shown in formula (11):

[0138] D * =(n *) 2 (11)

[0139] n * =n+iκ(12)

[0140] As an optional implementation, before step S3, the method further includes: performing baseline correction on the terahertz absorption spectrum and the terahertz dielectric loss spectrum using an adaptive iterative reweighted penalized least squares method (ie, airPLS algorithm).

[0141] Specifically, the terahertz absorption spectrum has a tendency to drift upward as a whole. Due to the deterioration of insulating oil, a large amount of polar substances will be produced, such as furfural, methanol, ethanol, formic acid, acetic acid, acetone and water. These polar substances have an absorption effect on terahertz waves. Therefore, the adaptive iterative reweighted penalty least squares method is selected to perform baseline correction on the terahertz absorption spectrum and the terahertz dielectric loss spectrum. The terahertz absorption spectrum and the dielectric loss spectrum after eliminating the baseline drift are as follows: Figure 8 and Fig. 9 As shown in Figure 2, the airPLS method adopts an error-based iterative weighting strategy, and the weight update of each point is based on the difference between the baseline of the previous cycle fitting and the original signal.

[0142] As an optional implementation, step S3 specifically includes:

[0143] Step S31 , measuring the dielectric loss, acid value and moisture content of the insulating oil deterioration standard sample respectively, and obtaining the dielectric loss measurement value, acid value measurement value and moisture measurement value of the insulating oil deterioration standard sample.

[0144] Specifically, the dielectric loss of the insulating oil deterioration standard sample was measured according to the measurement of relative permittivity, dielectric loss factor and DC resistivity of liquid insulating materials in GB / T5654-2007. The acid value of the insulating oil deterioration standard sample was measured according to the acid value determination method of petroleum products in GB / T 264-1983. The moisture content of the insulating oil deterioration standard sample was measured according to the moisture content determination method (coulometric method) of transformer oil and turbine oil in operation in GB / T7600-2014. The acid value of each insulating oil deterioration standard sample was tested twice, and the results were averaged. The parameter test results of the insulating oil deterioration standard sample are shown in Table 1.

[0145] Table 1 Parameter test results of insulating oil degradation standard sample

[0146]

[0147]

[0148] Step S32, fitting the relationship between the moisture characteristic parameter of the insulating oil degradation standard sample and the moisture measurement value to obtain the moisture terahertz calibration line.

[0149] The first 85 days of data were used for fitting calculations, and the following 95 and 128 days of data were used for verification. The fitting results of the moisture terahertz line are as follows:

[0150]

[0151] Step S33, fitting the relationship between the acid value characteristic parameter of the insulating oil degradation standard sample and the acid value measurement value to obtain the acid value terahertz calibration line.

[0152] According to the acid value characteristic parameters of the insulating oil deterioration standard sample and the acid value measurement value obtained by the national standard test, a scatter plot is drawn, such as Fig.10 As shown, it can be seen that there is a good positive correlation trend between the acid value characteristic parameters of the insulating oil deterioration standard sample and the acid value measurement value obtained by the national standard test. The Pearson correlation coefficient PCCS of the acid value characteristic parameters of the insulating oil deterioration standard sample and the acid value measurement value obtained by the national standard test is calculated, and the PCCS is 0.95905, which is close to 1. This proves that there is a strong correlation between the acid value characteristic parameters of the insulating oil deterioration standard sample and the acid value measurement value obtained by the national standard test. The expression of the straight line obtained by fitting the data is as follows:

[0153] acide.=-0.80625+2.5795P 2.1THz (14)

[0154] Wherein, acidide represents acid value; P 2.1THz Represents the characteristic parameter of acid value.

[0155] Calculate the goodness of fit R of the acid value characteristic parameters of the insulating oil deterioration standard sample and the acid value measurement value obtained by the national standard test 2 , and get R 2 It is greater than 0.9 and close to 1, indicating that the straight line can well represent the relationship between the acid value characteristic parameters of the insulating oil deterioration standard sample and the acid value measurement value obtained by the national standard test, and can be used as the terahertz calibration line of the insulating oil acid value.

[0156] Step S34, fitting the relationship between the dielectric loss characteristic parameter of the insulating oil degradation standard sample and the dielectric loss measurement value to obtain a dielectric loss terahertz calibration line.

[0157] According to the dielectric loss characteristic parameter DTa of the extracted insulating oil deterioration standard sample and the dielectric loss measurement value obtained by the national standard test, a scatter plot is drawn, such as Fig.11 As shown in the figure, it can be seen that there is a good positive correlation trend between the dielectric loss characteristic parameter DTa of the insulating oil deterioration standard sample and the dielectric loss measurement value obtained by the national standard test. The Pearson correlation coefficient PCCS is 0.92548, which is close to 1, proving that the dielectric loss characteristic parameter DTa of the insulating oil deterioration standard sample is TaThere is a strong correlation between the dielectric loss measurement value obtained by the national standard test and the expression of the straight line obtained by fitting the data is as follows:

[0158] tanδ . =-29.46733+1479.23534D Ta (15)

[0159] Wherein, tanδ represents the power frequency dielectric loss; D Ta Represents dielectric loss characteristic parameter.

[0160] R2 was calculated and found to be greater than 0.9 and close to 1, indicating that the straight line can well represent the relationship between the dielectric loss characteristic parameter DTa of the insulating oil degradation standard sample and the dielectric loss measurement value obtained by the national standard test, and can be used as the dielectric loss terahertz calibration line of the insulating oil.

[0161] As an optional implementation, in step S4, according to existing literature, there is a negative correlation between moisture content and breakdown voltage, and the negative correlation is related to the maximum applicable electric field of the insulating oil. Therefore, for the insulating oil, the relationship curve between moisture content and breakdown voltage can be obtained by fitting as follows: Fig.12 shown.

[0162] The breakdown voltage of the insulating oil is evaluated by evaluating the moisture content of the insulating oil. The relationship between the moisture content of the insulating oil deterioration standard sample and the breakdown voltage is expressed as:

[0163]

[0164] Wherein, Breakdown is the breakdown voltage of the insulating oil degradation standard sample, in kV; Oilwater is the water content of the insulating oil degradation standard sample, in ppm.

[0165] The expression of the terahertz line of the breakdown voltage of insulating oil is:

[0166]

[0167] Wherein, Breakdown represents the breakdown voltage; It represents the average refractive index in the low frequency band of the terahertz refraction spectrum; Indicates the average value of dielectric loss in the low frequency band of the terahertz dielectric loss spectrum; ΔPeak 1.7T The refractive index change value of the 1.7THz band relative to the low-frequency band in the terahertz refraction spectrum.

[0168] Beneficial effects of this application:

[0169] The present application can perform contactless and nondestructive testing on the functional characteristic parameters of mineral insulating oil. The method is simple and fast, and does not require sample extraction. While ensuring the accuracy of traditional methods, the present application overcomes the shortcomings of the existing acid value testing technology, such as the need for extraction, complexity and time-consuming, and poor anti-interference. The present application overcomes the shortcomings of the existing dielectric loss testing technology, such as the long testing time, susceptibility to external interference, low level of automation, and poor versatility. The present application overcomes the large dispersion of the existing breakdown voltage testing technology and the high-voltage lossy testing (a sample needs to be broken down multiple times, and the national standard requires more than 6 times, but in fact the sample is different after being broken down once, and the breakdown will produce impurities, such as carbon particles, methanol, etc., which is equivalent to each breakdown being the result of several breakdowns of the original performance). The present application can realize on-site nondestructive and rapid testing of the functional characteristic parameters of transformer insulating oil, and effectively ensure the safe operation of the transformer.

[0170] Furthermore, the following will use the method for determining the functional characteristic parameters of mineral insulating oil based on terahertz of the present application to obtain the dielectric loss prediction value, acid value prediction value and breakdown voltage prediction value of the insulating oil to be tested, and test the breakdown voltage, dielectric loss and acid value of the insulating oil to be tested according to the national standard method, and compare them to verify the feasibility of the method for determining the functional characteristic parameters of mineral insulating oil based on terahertz of the present application. The specific results of the dielectric loss prediction value, acid value prediction value and breakdown voltage prediction value of the insulating oil to be tested are shown in Tables 2-4.

[0171] 1) Dielectric loss

[0172] Table 2 Dielectric loss prediction results of the tested insulating oil

[0173] Insulating oil to be tested Dielectric loss prediction value for this application (%) GB / T5654-2007 dielectric loss test value (%) High dielectric loss 11.987 12.039 Low dielectric loss 0.265 0.319

[0174] It can be found that, for both high dielectric loss insulating oil and low dielectric loss insulating oil, the dielectric loss prediction value obtained by the present application is basically consistent with the standard measurement method, with an error of less than 0.1% and high accuracy.

[0175] 2) Acid value

[0176] Table 3 Acid value prediction results of the tested insulating oil

[0177] Insulating oil to be tested Acid value prediction for this application (mgKOH / g) GB / T264-1983 acid value test value (mgKOH / g) High acid value 1.579 1.586 Low acid value 0.049 0.034

[0178] It can be seen that, whether it is the insulating oil with high acid value or the insulating oil with low acid value, the predicted acid value obtained by the present application is basically consistent with the standard measurement method, the error is less than 0.02 mgKOH / g, and the accuracy is relatively high.

[0179] 3) Breakdown voltage

[0180] Table 4 Prediction results of breakdown voltage of tested insulating oil

[0181] Insulating oil to be tested Predicted breakdown voltage of this application (kV) GB / T7600-2014 Breakdown voltage test value (kV) High breakdown voltage 47.372 49.5 Low breakdown voltage 30.816 33.4

[0182] It can be seen that for the breakdown voltage, the error is less than 3kV. Although the effect is not as small as the errors of dielectric loss and acid value, the national standard boost method for breakdown voltage testing also has dispersion. At present, this result can meet actual needs.

[0183] In summary, the method for determining the functional characteristic parameters of mineral insulating oil based on terahertz in the present application has good feasibility and accuracy.

[0184] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0185] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and 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 embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. 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), magnetic 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 may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0186] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0187] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0188] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for determining the functional characteristic parameters of mineral insulating oil based on terahertz, characterized in that: The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz comprises: preparing insulating oil degradation standard samples and obtaining terahertz time-domain spectra of the insulating oil degradation standard samples; Extracting characteristic parameters of the insulating oil deterioration standard sample based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample; the characteristic parameters include moisture characteristic parameters, acid value characteristic parameters and dielectric loss characteristic parameters; Determine the insulating oil terahertz marking line based on the characteristic parameters of the insulating oil degradation standard sample; the insulating oil terahertz marking line includes a moisture terahertz marking line, an acid value terahertz marking line and a dielectric loss terahertz marking line; Determine the relationship between the moisture content and the breakdown voltage of the insulating oil deterioration standard sample, and determine the breakdown voltage terahertz calibration line based on the relationship between the moisture content and the breakdown voltage of the insulating oil deterioration standard sample and the insulating oil moisture terahertz calibration line; Acquire a terahertz time-domain spectrum of the insulating oil to be tested, and extract characteristic parameters of the insulating oil to be tested based on the terahertz time-domain spectrum of the insulating oil to be tested; Based on the characteristic parameters of the insulating oil to be tested, the breakdown voltage terahertz line, the acid value terahertz line and the dielectric loss terahertz line, the predicted values ​​of the functional characteristic parameters of the insulating oil to be tested are determined; the functional characteristic parameters include the breakdown voltage, the acid value and the dielectric loss.

2. The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz according to claim 1, characterized in that: Obtain the terahertz time domain spectrum of the insulating oil degradation standard, including: Select a polystyrene standard cuvette with a set optical path as the sample cell, and use the corresponding empty cuvette as the reference sample cell; Under a set temperature and set humidity environment, a transmission terahertz spectrometer is used to irradiate the insulating oil degradation standard sample contained in the sample pool and the reference sample pool, respectively, to obtain a terahertz time-domain spectrum of the insulating oil degradation standard sample and a corresponding reference terahertz time-domain spectrum.

3. The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz according to claim 2, characterized in that: Based on the terahertz time-domain spectrum of the insulating oil degradation standard sample, the characteristic parameters of the insulating oil degradation standard sample are extracted, including: Determine the refractive index of the insulating oil deterioration standard sample based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample, and plot the terahertz refraction spectrum of the insulating oil deterioration standard sample based on the refractive index of the insulating oil deterioration standard sample; Determine the absorption coefficient of the insulating oil deterioration standard sample based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample and the refractive index of the insulating oil deterioration standard sample, and plot the terahertz absorption spectrum of the insulating oil deterioration standard sample based on the absorption coefficient of the insulating oil deterioration standard sample; Determine the dielectric loss of the insulating oil deterioration standard sample based on the refractive index of the insulating oil deterioration standard sample and the extinction coefficient of the insulating oil deterioration standard sample, and draw a terahertz dielectric loss spectrum of the insulating oil deterioration standard sample based on the dielectric loss of the insulating oil deterioration standard sample; the extinction coefficient is obtained based on the terahertz time domain spectrum of the insulating oil deterioration standard sample and the refractive index of the insulating oil deterioration standard sample; Based on terahertz refraction spectrum and terahertz dielectric loss spectrum, the moisture characteristic parameters of insulating oil degradation standard samples are extracted; Based on terahertz absorption spectroscopy, the acid value characteristic parameters of insulating oil deterioration standard samples are extracted; Based on the terahertz dielectric loss spectrum, the dielectric loss characteristic parameters of the insulating oil degradation standard sample are extracted.

4. The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz according to claim 3, characterized in that: Based on the terahertz time-domain spectrum of the insulating oil degradation standard sample, the refractive index of the insulating oil degradation standard sample is determined, specifically including: Based on the terahertz time-domain spectrum of the insulating oil deterioration standard sample, a terahertz frequency-domain spectrum of the insulating oil deterioration standard sample is obtained, and a frequency-domain phase of the terahertz frequency-domain spectrum of the insulating oil deterioration standard sample is determined; Based on the reference terahertz time-domain spectrum, determining a reference terahertz frequency-domain spectrum, and determining a frequency-domain phase of the reference terahertz frequency-domain spectrum; The refractive index of the insulating oil deterioration standard sample is determined based on the frequency domain phase of the terahertz frequency domain spectrum of the insulating oil deterioration standard sample and the frequency domain phase of the reference terahertz frequency domain spectrum.

5. The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz according to claim 4, characterized in that: The absorption coefficient of the insulating oil degradation standard sample is determined based on the terahertz time domain spectrum of the insulating oil degradation standard sample and the refractive index of the insulating oil degradation standard sample, specifically including: Based on the terahertz frequency domain spectrum of the insulating oil degradation standard sample, the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil degradation standard sample is determined; Based on the reference terahertz frequency domain spectrum, determining the frequency domain amplitude of the reference terahertz frequency domain spectrum; Determine the extinction coefficient of the insulating oil deterioration standard sample based on the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil deterioration standard sample, the frequency domain amplitude of the reference terahertz frequency domain spectrum, and the refractive index of the insulating oil deterioration standard sample; Based on the extinction coefficient of the insulating oil deterioration standard sample, the absorption coefficient of the insulating oil deterioration standard sample is determined.

6. The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz according to claim 5, characterized in that: The expression of the extinction coefficient of the insulating oil degradation standard is: Wherein, κ(ω) is the extinction coefficient of the insulating oil deterioration standard sample; c is the speed of light in a vacuum; d is the thickness of the insulating oil deterioration standard sample; ω is the angular frequency; n is the refractive index of the insulating oil deterioration standard sample; A s (ω) is the frequency domain amplitude of the terahertz frequency domain spectrum of the insulating oil degradation standard sample; A r (ω) is the frequency domain amplitude of the reference terahertz frequency domain spectrum; The expression of the absorption coefficient of the insulating oil degradation standard is: α(ω)=2κ(ω)ω / c; Where α(ω) is the absorption coefficient of the insulating oil degradation standard.

7. The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz according to claim 6, characterized in that: The dielectric loss of the insulating oil deterioration standard sample is determined based on the refractive index of the insulating oil deterioration standard sample and the extinction coefficient of the insulating oil deterioration standard sample, specifically including: Based on the refractive index and extinction coefficient of the insulating oil deterioration standard sample, the real part of the dielectric constant and the imaginary part of the dielectric constant of the insulating oil deterioration standard sample are determined; The dielectric loss of the insulating oil deterioration standard sample is determined based on the real part of the dielectric constant and the imaginary part of the dielectric constant of the insulating oil deterioration standard sample.

8. The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz according to claim 7, characterized in that: The real part of the dielectric constant D of the insulation oil deterioration standard sample r The expression is: D r (ω)=n(ω) 2 -k(oh) 2 ; Imaginary part D of dielectric constant of insulating oil deterioration standard sample i The expression is: D i (ω)=2n(ω)κ(ω); Dielectric loss D of insulating oil deterioration standard sample T The expression is:

9. The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz according to claim 1, characterized in that: Determining the insulating oil terahertz marking line based on the characteristic parameters of the insulating oil degradation standard sample specifically includes: The dielectric loss, acid value and moisture content of the insulating oil deterioration standard sample are measured respectively to obtain the dielectric loss measurement value, acid value measurement value and moisture measurement value of the insulating oil deterioration standard sample; The relationship between the moisture characteristic parameters of the insulating oil degradation standard sample and the moisture measurement value is fitted to obtain the moisture terahertz calibration line; The relationship between the acid value characteristic parameters of the insulating oil degradation standard sample and the acid value measurement value is fitted to obtain the acid value terahertz calibration line; The relationship between the dielectric loss characteristic parameters of the insulating oil degradation standard sample and the dielectric loss measurement value is fitted to obtain the dielectric loss terahertz calibration line.

10. The method for determining the functional characteristic parameters of mineral insulating oil based on terahertz according to claim 1, characterized in that: The expression for the relationship between the moisture content and breakdown voltage of the insulating oil deterioration standard sample is: Among them, Breakdown represents the breakdown voltage; e represents the natural constant; Oilwater represents the water content of the insulating oil; The expression of the terahertz line of the breakdown voltage of insulating oil is: Wherein, Breakdown represents the breakdown voltage; It represents the average refractive index in the low frequency band of the terahertz refraction spectrum; Indicates the average value of dielectric loss in the low frequency band of the terahertz dielectric loss spectrum; ΔPeak 1.7T The refractive index change value of 1.7THz band relative to the low frequency band in the terahertz refraction spectrum; The expression of the dielectric loss terahertz line of insulating oil is: <h2 style=";text-align:left;direction:ltr">tanδ.=-29.46733+1479.23534D<h2 style=";text-align:left;direction:ltr"> Ta <h2 style=";text-align:left;direction:ltr"> ; Wherein, tanδ represents the power frequency dielectric loss; D Ta Indicates dielectric loss characteristic parameter; The expression of the acid value terahertz line is: acid=-0.80625+2.5795P 2.1THz ; Wherein, acidide represents acid value; P 2.1THz Represents the characteristic parameter of acid value.

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