Method and device for detecting moisture content of insulating material

Abstract

The invention discloses a method and device for detecting the moisture content of an insulating material, and relates to the field of insulating material detection.The method comprises the steps that a to-be-detected transmission terahertz time-domain signal is obtained; the to-be-detected transmission terahertz time-domain signal is a time-domain signal obtained after terahertz waves are emitted to the to-be-detected insulating material and penetrate through the to-be-detected insulating material; converting the to-be-measured transmission terahertz time domain signal into a frequency domain signal to obtain a to-be-measured transmission terahertz frequency domain signal; performing feature extraction on the to-be-measured transmission terahertz time domain signal and the to-be-measured transmission terahertz frequency domain signal to obtain terahertz frequency spectrum features of the to-be-measured insulating material; the terahertz frequency spectrum characteristics comprise a time domain signal peak value difference value and an absorption coefficient integral value; and determining the moisture content of the to-be-detected insulating material according to the terahertz frequency spectrum characteristics of the to-be-detected insulating material and the quantitative curve of the terahertz frequency spectrum characteristics and the moisture, and realizing nondestructive detection of the moisture content of the to-be-detected insulating material.

Description

Technical Field

[0001] The present application relates to the field of insulating material detection, and in particular to a method and device for detecting moisture content in insulating materials. Background Art

[0002] Insulating materials are widely used in power equipment. Take mineral oil-impregnated fiber insulation paper (i.e. oil-paper insulation) as an example. As a classic composite insulation material, it is widely used in ultra-high voltage and large-capacity oil-immersed power equipment. Its insulation performance is closely related to the moisture content. The increase in moisture will not only cause a significant drop in electrical strength, but also double the aging rate of the material, which is an important factor threatening the safe operation of the equipment. Therefore, accurately obtaining the moisture content of insulating materials is crucial for early warning of power equipment failures. "DL / T596-2021 Preventive Test Procedure for Power Equipment" makes detailed requirements for the moisture content of each insulating material before commissioning and during operation.

[0003] The relevant standard detection methods are to use the Karl Fischer method (IEC 60814 and GB / T 462) and the Coulomb method (GB / T7600) to test the moisture content of insulating materials. Although accurate, they have disadvantages such as loss, complex testing and time-consuming. In particular, the moisture content test of solid insulating materials requires destroying the insulation for sampling and testing, which is difficult to apply before leaving the factory or during maintenance, and can often only be carried out by random inspection. There is resistance to the promotion of DL / T596-2021 in actual field applications. Summary of the invention

[0004] The purpose of this application is to provide a method and device for detecting the moisture content of an insulating material, which can realize non-destructive detection of the moisture content of the insulating material.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a method for detecting moisture content of an insulating material, comprising:

[0007] Acquire a transmitted terahertz time domain signal to be measured; the transmitted terahertz time domain signal to be measured is a time domain signal after a terahertz wave is emitted to the insulating material to be measured and the terahertz wave is transmitted through the insulating material to be measured;

[0008] Converting the transmitted terahertz time domain signal to be measured into a frequency domain signal to obtain the transmitted terahertz frequency domain signal to be measured;

[0009] Extracting features of the transmitted terahertz time domain signal to be measured and the transmitted terahertz frequency domain signal to be measured to obtain terahertz spectrum features of the insulating material to be measured; the terahertz spectrum features include: a time domain signal peak difference and an absorption coefficient integral value;

[0010] The moisture content of the insulating material to be tested is determined according to the terahertz spectrum characteristics of the insulating material to be tested and a quantitative curve between the terahertz spectrum characteristics and moisture.

[0011] Optionally, before determining the moisture content of the insulating material to be tested according to the terahertz spectrum characteristics of the insulating material to be tested and the quantitative curve between the terahertz spectrum characteristics and moisture, the insulating material moisture content detection method further includes:

[0012] Acquire a standard transmission terahertz time domain signal; the standard transmission terahertz time domain signal comprises: emitting terahertz waves to standard insulating materials with different moisture contents, and a time domain signal after the terahertz waves are transmitted through the standard insulating materials;

[0013] Converting the standard transmission terahertz time domain signal into a frequency domain signal to obtain a standard transmission terahertz frequency domain signal;

[0014] Performing feature extraction on the standard transmission terahertz time domain signal and the standard transmission terahertz frequency domain signal to obtain the terahertz spectrum feature of the standard insulating material;

[0015] According to the terahertz spectrum characteristics and the corresponding real moisture content of the standard insulating material, a statistical model is used to construct a quantitative curve of the terahertz spectrum characteristics and moisture.

[0016] Optionally, determining the moisture content of the insulating material to be tested according to the terahertz spectrum characteristics of the insulating material to be tested and a quantitative curve of the terahertz spectrum characteristics and moisture includes:

[0017] Normalizing the terahertz spectrum characteristics of the insulating material to be tested to obtain normalized terahertz spectrum characteristics of the insulating material to be tested;

[0018] The normalized terahertz spectrum characteristics of the insulating material to be tested are substituted into the quantitative curve of the terahertz spectrum characteristics and moisture to obtain the moisture content of the insulating material to be tested.

[0019] Optionally, the expression of the quantitative curve of terahertz spectrum characteristics and moisture is:

[0020] Oil_water=a+b*T D +c*S α ;

[0021] Among them, Oil_water represents the moisture content of the insulating material to be tested; T D represents the normalized peak value difference of the time domain signal; S α represents the normalized integral value of the absorption coefficient; a, b and c are fitting parameters.

[0022] Optionally, converting the to-be-measured transmitted terahertz time domain signal into a frequency domain signal to obtain the to-be-measured transmitted terahertz frequency domain signal specifically includes:

[0023] The transmitted terahertz time domain signal to be measured is converted into a frequency domain signal by using Fourier transform and Fresnel formula to obtain the transmitted terahertz frequency domain signal to be measured.

[0024] Optionally, the transmitted terahertz time domain signal to be measured is converted into a frequency domain signal by using Fourier transform and Fresnel formula to obtain the transmitted terahertz frequency domain signal to be measured, which specifically includes:

[0025] The transmitted terahertz time domain signal to be measured is converted by Fourier transform to obtain a frequency domain amplitude to be measured and a frequency domain phase to be measured;

[0026] According to the frequency domain amplitude to be measured and the frequency domain phase to be measured, the refractive index and extinction coefficient of the insulating material to be measured are calculated using the Fresnel formula, and the absorption coefficient of the insulating material to be measured is calculated according to the refractive index and extinction coefficient of the insulating material to be measured; the transmitted terahertz frequency domain signal to be measured includes: the absorption coefficient of the insulating material to be measured.

[0027] Optionally, the time domain signal peak difference is the decrease value of the transmitted terahertz time domain signal compared with the reference time domain signal; the absorption coefficient integral value is the integral value of the absorption spectrum of the transmitted terahertz frequency domain signal within a set spectral range; the reference time domain signal is a time domain signal after the terahertz wave is transmitted through the reference object after emitting a terahertz wave to the reference object; the reference object is air, an empty cuvette, or a cuvette with a blank insulating material.

[0028] Optionally, the actual moisture content is obtained by testing the moisture content of the standard insulating material using a coulometric method.

[0029] In a second aspect, the present application provides an insulating material moisture content detection device, comprising: a terahertz transmitter, a cuvette, a terahertz receiver and a processing device; the terahertz transmitter and the processing device are connected;

[0030] The cuvette is used to hold the insulating material to be tested; the terahertz transmitter is used to transmit terahertz waves to the insulating material to be tested in the cuvette; the terahertz receiver is used to receive the time domain signal after the terahertz wave passes through the insulating material to be tested, and send the obtained transmitted terahertz time domain signal to be tested to the processing device; the processing device is used to execute the above-mentioned insulating material moisture content detection method.

[0031] Optionally, the insulating material moisture content detection device further comprises: a first reflector, a first focusing lens, a second reflector and a second focusing lens;

[0032] The first reflector is arranged on the output light path of the terahertz transmitter; the first focusing lens is arranged on the reflected light path of the first reflector; the cuvette is arranged on the transmitted light path of the first focusing lens; the second focusing lens is arranged on the output light path of the cuvette; the second reflector is arranged on the transmitted light path of the second focusing lens; and the terahertz receiver is arranged on the reflected light path of the second reflecting lens.

[0033] According to the specific embodiments provided in this application, this application has the following technical effects:

[0034] The present application provides a method and device for detecting moisture content of an insulating material. The method transmits a terahertz wave to the insulating material to be tested, obtains a transmitted terahertz time domain signal to be tested after the terahertz wave has passed through the insulating material to be tested, and obtains a terahertz spectrum feature including a time domain signal peak difference and an absorption coefficient integral value through time-frequency conversion and feature extraction of the transmitted terahertz time domain signal to be tested. The moisture content of the insulating material to be tested is determined based on the terahertz spectrum feature and a quantitative curve of the terahertz spectrum feature and moisture. The present application does not require the destruction of the insulating material to be tested, thereby realizing non-destructive detection of the moisture content of the insulating material, and at the same time overcomes the disadvantages of high cost, complexity, time-consuming, poor anti-interference, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] 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.

[0036] Figure 1 A flow chart of a method for detecting moisture content of an insulating material provided in one embodiment of the present application;

[0037] Figure 2 A structural diagram of a device for detecting moisture content in an insulating material provided by another embodiment of the present application;

[0038] Figure 3 A specific flow chart of a method for detecting moisture content in insulating oil provided in another embodiment of the present application;

[0039] Figure 4 A schematic diagram of the relationship between amplitude and time provided in an embodiment of the present application;

[0040] Figure 5 A schematic diagram of a terahertz absorption spectrum provided in one embodiment of the present application.

[0041] Figure numerals: terahertz transmitter—1; terahertz receiver—2; first reflector—3; first focusing lens—4; stage—5; cuvette—6; cuvette cover—7; second reflector—8; second focusing lens—9. DETAILED DESCRIPTION

[0042] 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.

[0043] 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 with reference to the accompanying drawings and specific implementation methods.

[0044] In order to realize non-destructive detection of moisture content in insulating materials, the present application detects moisture content in insulating materials based on terahertz waves. Terahertz waves refer to electromagnetic radiation waves with a wavelength of 0.1THz to 10THz and a wavelength greater than 30um and less than 3mm. Terahertz waves are located between millimeter waves and infrared waves in the electromagnetic spectrum, and belong to the frequency band of transition from macroscopic electronics to microscopic photonics. They have unique perception capabilities for the vibration of covalent bonds in polymers, hydrogen bond stretching, and phonon vibration modes. They have high permeability, fingerprint characteristics, low energy, water absorption, and high resolution, and are very suitable for evaluating the moisture content of insulating oils.

[0045] In an exemplary embodiment, Figure 1 As shown, a method for detecting moisture content of an insulating material is provided, comprising:

[0046] Step 101, obtaining a transmitted terahertz time domain signal to be measured; the transmitted terahertz time domain signal to be measured is a time domain signal after a terahertz wave is emitted to an insulating material to be measured and the terahertz wave passes through the insulating material to be measured.

[0047] Step 102: convert the to-be-measured transmitted terahertz time domain signal into a frequency domain signal to obtain the to-be-measured transmitted terahertz frequency domain signal.

[0048] Step 103, extracting features of the to-be-tested transmitted terahertz time domain signal and the to-be-tested transmitted terahertz frequency domain signal to obtain terahertz spectrum features of the to-be-tested insulating material; the terahertz spectrum features include: a time domain signal peak difference and an absorption coefficient integral value.

[0049] Step 104: determining the moisture content of the insulating material to be tested according to the terahertz spectrum characteristics of the insulating material to be tested and the quantitative curve between the terahertz spectrum characteristics and moisture.

[0050] The implementation of the above steps 101 to 104 can realize non-destructive detection of the moisture content of the insulating material, while also overcoming the shortcomings of high cost, complexity and time consumption, and poor anti-interference performance.

[0051] In another exemplary embodiment of the present application, the time domain signal peak difference is the decrease value of the transmitted terahertz time domain signal compared with the reference time domain signal; the absorption coefficient integral value is the integral value of the absorption spectrum of the transmitted terahertz frequency domain signal within the set spectral range.

[0052] The set spectral range is related to the signal-to-noise ratio of the device implementing the method. The set spectral range used in this embodiment is [0.3 THz, 1 THz].

[0053] The reference time domain signal is a time domain signal after the terahertz wave is transmitted through the reference object after emitting the terahertz wave to the reference object. The reference object is air, an empty cuvette (i.e., no insulating material is placed) or a cuvette with blank insulating material (i.e., dry insulating material). The reference object used in this embodiment is an empty cuvette.

[0054] In another exemplary embodiment of the present application, step 102 specifically includes:

[0055] The transmitted terahertz time domain signal to be measured is converted into a frequency domain signal by using Fourier transform and Fresnel formula to obtain the transmitted terahertz frequency domain signal to be measured. Specifically:

[0056] (1) The transmitted terahertz time domain signal to be measured is converted by Fourier transform to obtain a frequency domain amplitude to be measured and a frequency domain phase to be measured.

[0057] If the transmitted terahertz time domain signal is expressed as E(t), the Fourier transform is used to transform the transmitted terahertz time domain signal into the frequency domain amplitude A(ω) and the frequency domain phase φ(ω), which are expressed as follows:

[0058]

[0059] E(ω) is the frequency domain expression of the transmitted terahertz time domain signal; t represents time; ω represents angular frequency; and i represents an imaginary unit.

[0060] (2) According to the frequency domain amplitude to be measured and the frequency domain phase to be measured, the refractive index and extinction coefficient of the insulating material to be measured are calculated using the Fresnel formula, and the absorption coefficient of the insulating material to be measured is calculated according to the refractive index and extinction coefficient of the insulating material to be measured; the transmitted terahertz frequency domain signal to be measured includes: the absorption coefficient of the insulating material to be measured.

[0061] Among them, the Fresnel formula is expressed as:

[0062] n(ω)=1+[φ s (ω)-φ r (ω)]c / dω;

[0063]

[0064] α(ω)=2κ(ω)ω / c;

[0065] n(ω) is the refractive index; κ(ω) is the extinction coefficient; α(ω) is the absorption coefficient, the unit is cm -1 ; φ s (ω) represents the frequency domain phase to be measured; φ r (ω) represents the frequency domain phase of the reference frequency domain signal; A s (ω) represents the frequency domain amplitude to be measured; A r (ω) represents the frequency domain amplitude of the reference frequency domain signal; the reference frequency domain signal is obtained by converting the reference time domain signal using Fourier transform; c represents the speed of light in vacuum, in cm / s; d represents the thickness of the insulating material to be tested, in cm.

[0066] In another exemplary embodiment of the present application, step 104 specifically includes:

[0067] (1) normalizing the terahertz spectrum characteristics of the insulating material to be tested to obtain the normalized terahertz spectrum characteristics of the insulating material to be tested. (2) substituting the normalized terahertz spectrum characteristics of the insulating material to be tested into a quantitative curve of terahertz spectrum characteristics and moisture to obtain the moisture content of the insulating material to be tested.

[0068] Among them, the expression of the quantitative curve of terahertz spectrum characteristics and moisture is:

[0069] Oil_water=a+b*T D +c*S α ;

[0070] Where Oil_water represents the moisture content of the insulation material to be tested, in mg / L or ppm; T D represents the normalized peak value difference of the time domain signal; S α represents the normalized integral value of the absorption coefficient; a, b and c are fitting parameters, and the values ​​of a, b and c can be 30.7, 1.0401 and 20.262 respectively.

[0071] In another exemplary embodiment of the present application, before step 104, the method for detecting moisture content in insulating materials further includes: constructing a quantitative curve of terahertz spectrum characteristics and moisture.

[0072] Construct a quantitative curve of terahertz spectrum characteristics and moisture, including:

[0073] (1) Obtaining a standard transmission terahertz time domain signal; the standard transmission terahertz time domain signal comprises: emitting a terahertz wave to a standard insulating material with different moisture contents, and a time domain signal after the terahertz wave transmits through the standard insulating material.

[0074] (2) Converting the standard transmission terahertz time domain signal into a frequency domain signal to obtain a standard transmission terahertz frequency domain signal. The specific implementation of this step is similar to the specific implementation of the above step 102, and will not be repeated here.

[0075] (3) Extracting features of the standard transmitted terahertz time domain signal and the standard transmitted terahertz frequency domain signal to obtain terahertz spectrum features of the standard insulating material.

[0076] (4) According to the terahertz spectrum characteristics and the corresponding true moisture content of the standard insulating material, a statistical model is used to construct a quantitative curve of the terahertz spectrum characteristics and moisture. The true moisture content can be obtained by testing the moisture content of the standard insulating material using the Coulomb method; the statistical model can be a multiple regression model.

[0077] In this step, when constructing a quantitative curve of terahertz spectrum characteristics and moisture, the terahertz spectrum characteristics of the standard insulating material are first normalized to obtain the normalized terahertz spectrum characteristics of the standard insulating material; then, based on the normalized terahertz spectrum characteristics of the standard insulating material, a statistical model is used to construct a quantitative curve of terahertz spectrum characteristics and moisture.

[0078] Based on the same inventive concept, the embodiment of the present application also provides an insulating material moisture content detection device for implementing the above-mentioned insulating material moisture content detection method. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above-mentioned method, so the specific limitations in one or more embodiments of the insulating material moisture content detection device provided below can refer to the limitations of the insulating material moisture content detection method above, and will not be repeated here.

[0079] In an exemplary embodiment, Figure 2 As shown, a device for detecting moisture content of an insulating material is provided, comprising: a terahertz transmitter 1, a cuvette 6, a terahertz receiver 2 and a processing device; the terahertz transmitter 1 is connected to the processing device.

[0080] The cuvette 6 is used to hold the insulating material to be tested; the terahertz transmitter 1 is used to transmit terahertz waves to the insulating material to be tested in the cuvette 6; the terahertz receiver 2 is used to receive the time domain signal after the terahertz wave passes through the insulating material to be tested, and send the obtained transmitted terahertz time domain signal to be tested to the processing device; the processing device is used to execute the above-mentioned insulating material moisture content detection method.

[0081] As an optional implementation, please refer to Figure 2 The insulating material moisture content detection device also includes: a first reflector 3, a first focusing lens 4, a second reflector 8 and a second focusing lens 9.

[0082] The first reflector 3 is arranged on the output light path of the terahertz transmitter 1; the first focusing lens 4 is arranged on the reflected light path of the first reflector 3; the cuvette 6 is arranged on the transmitted light path of the first focusing lens 4; the second focusing lens 9 is arranged on the output light path of the cuvette 6; the second reflector 8 is arranged on the transmitted light path of the second focusing lens 9; and the terahertz receiver 2 is arranged on the reflected light path of the second reflector.

[0083] As an optional implementation, please refer to Figure 2 The insulating material moisture content detection device also includes: a loading platform 5; the loading platform 5 is used to place the cuvette 6.

[0084] As an optional implementation, please refer to Figure 2 The insulating material moisture content detection device further includes: a cuvette cover 7; the cuvette cover 7 is used to cover the cuvette 6.

[0085] Take the insulating oil in the following insulating material as an example. Figure 3 , the insulating material moisture content detection method and device of the above embodiment are further described in detail, and the effectiveness of the scheme is verified.

[0086] This embodiment mainly uses the strong sensing ability of terahertz waves for moisture. First, the terahertz spectrum characteristics are extracted by testing some oil samples to establish a quantitative relationship with moisture. Then, the terahertz time-frequency spectrum of the sample to be tested is directly measured, and the moisture content is evaluated using the quantitative relationship established previously.

[0087] (1) Obtain insulating oil samples with different moisture contents.

[0088] Accurately measure 500ml of fully dried insulating oil into a clean and fully dried aluminum bottle, put a clean stirring bar, use a micro-injector to add 80uL of pure water to the liquid insulating material (i.e. insulating oil), seal the aluminum bottle, ultrasonically vibrate at 80℃ for 1h, and stir at 80℃ for 1h until the water is completely dissolved. After stirring, quickly divide it into 20mL headspace gas phase bottles, dry it in a vacuum drying oven at 50pa / 90℃, and set the drying time to 0h, 1h, 2h, 3h, 8h, 12h, 24h, and 40h respectively. Prepare gradient moisture content liquid insulation samples according to the gradient drying time, and determine their moisture content according to GB / T 7600.

[0089] It should be noted that: ① Different insulating oils have different water retention capabilities, and different gradient drying times should be set according to the influence of different conditions. ② The standard sample should be from the same source as the test sample. ③ If the water is not completely dissolved, it is necessary to repeatedly shake and stir until the water is completely dissolved and there is no visible suspended free liquid water. ④ The standard sample is sealed in a headspace gas phase bottle and refrigerated at 4°C, with a storage period of 1 year.

[0090] (2) Measure the moisture content of the standard sample.

[0091] The moisture content of insulating oil was measured according to GB / T 7600-2014. The moisture content of each sample was tested twice and the results were averaged. The test results of moisture content of standard samples are shown in Table 1.

[0092] Table 1 Test results of moisture content of standard samples

[0093] Serial number Water mg / L 1 60.5 2 53.1 3 47.9 4 42.9 5 21.7 6 10.9 7 6.93 8 5.3 9 7

[0094] (3) Measure the terahertz spectrum of the standard sample (terahertz time domain spectrum and terahertz frequency domain spectrum).

[0095] ①Measure the terahertz time-domain spectrum of the standard sample (i.e., the transmitted terahertz time-domain signal).

[0096] Using a transmission terahertz spectrometer, a polystyrene standard cuvette 6 (capacity 4.5 mL) with a 10 mm optical path was selected to non-destructively measure the terahertz spectrum of the standard sample insulating oil at 25°C and 5% humidity. Two portions of each sample were taken, and the average value of 256 tests was taken for each portion (taking about 2 minutes).

[0097] a) Prepare the test sample. Take out the clean cuvette 6 from the side, use a pipette to measure an appropriate amount of standard insulating liquid material sample into the cuvette 6, cover the cuvette cover 7 and seal it for storage. Do not touch the front and rear light path of the cuvette 6 during the whole process.

[0098] b) Obtain the terahertz time domain signal transmitted by the standard sample. Place the sample prepared in a) on the stage 5, making sure it is located at the center of the terahertz optical path. If the terahertz probe is equipped with a lens, ensure that the sample is placed at the focus of the terahertz wave, and the spot size must be less than 40% of the width of the incident surface of the cuvette 6. The cuvette 6 should have a front and back distinction, and the orientation should be consistent during the test. Then obtain the terahertz time domain signal transmitted by the standard sample. The terahertz time domain signal transmitted by the sample to be tested is also obtained in the above method. The device for determining the water content of a sample by terahertz transmission method is as follows: Figure 2 shown.

[0099] The terahertz pulse is directed to the sample through the photoconductive antenna. After penetrating the sample, the terahertz pulse carrying the sample information is captured by the terahertz receiver 2 to obtain the terahertz time domain spectrum signal. As the water content increases, the sample's absorption of the terahertz wave gradually increases, and the transmission intensity decreases accordingly, so the peak value of the sample signal decreases; at the same time, as the water content increases, the dielectric constant of the oil paper sample increases. For a medium with a higher dielectric constant, the propagation speed of electromagnetic waves inside it is lower, so the peak time will be delayed as the water content increases. The relationship between amplitude and time is shown in Figure 4 shown.

[0100] ② Determine the terahertz time domain spectrum of the standard sample (i.e., the transmitted terahertz frequency domain signal).

[0101] The terahertz time domain signal of the sample to be tested is converted into a spectrum of amplitude and phase through Fourier transform, and then the refractive index and extinction coefficient of the insulating oil are calculated using the Fresnel formula, and the absorption coefficient of the insulating oil is calculated based on the refractive index and extinction coefficient of the insulating oil. The specific calculation formula is not repeated here. The terahertz absorption spectrum of the standard sample is as follows: Figure 5 shown.

[0102] (4) Feature extraction

[0103] from Figure 5 It can be seen that the absorption coefficient spectrum amplitude of the sample shows a gradual upward trend with the increase of the water content of the sample. Therefore, there is a certain correlation between the moisture content of the insulating oil and the time domain peak and absorption coefficient. This study is used to study the relationship between the moisture content of the insulating oil and the terahertz time-frequency spectrum.

[0104] For the time domain signal, the terahertz time domain peak gradually decreases with the increase of moisture content. For the frequency domain signal, the terahertz absorption spectrum gradually increases with the increase of moisture content. Therefore, the decrease value of the terahertz time domain signal peak value of the insulating oil relative to the empty cuvette and the integral value of the frequency domain signal absorption spectrum from 0.3THz to 1THz are considered as the characteristic parameters of the moisture content of the insulating oil. The time domain signal peak difference is shown in Table 2, and the absorption coefficient integral value is shown in Table 3.

[0105] Table 2 Time domain signal peak difference

[0106] Serial number Peak value difference of time domain signal 1 1216.662 2 1186.222 3 1192.276 4 1141.522 5 1064.284 6 978.137 7 992.568 8 947.157 9 962.158

[0107] Table 3 Absorption coefficient integral value

[0108]

[0109]

[0110] (5) Establish a quantitative curve between terahertz spectrum characteristics and moisture content in insulating oil.

[0111] The extracted characteristic parameters are normalized, and the normalized terahertz time-frequency domain characteristic parameters are shown in Table 4.

[0112] Table 4 Normalized terahertz time-frequency domain characteristic parameters

[0113] Serial number <![CDATA[Peak difference T of the normalized time-domain signal D > <![CDATA[Integrated value S of the normalized absorption coefficient α > 1 1.287 1.675 2 1.009 0.995 3 1.065 0.794 4 0.601 0.212 5 -0.104 -0.036 6 -0.890 -0.549 7 -0.759 -0.865 8 -1.173 -1.146 9 -1.036 -1.080

[0114] Establish a multiple regression model Oil_water=a+b*T D +c*S α The fitted model is Oil_water = 30.7 + 1.0401 * T D +20.262*S α , the root mean square error is 1.79, and the goodness of fit R 2 It is 0.995, indicating that the model has an excellent fitting effect.

[0115] (6) Test the terahertz spectrum of the sample and calculate the moisture content.

[0116] The terahertz spectrum of the sample to be tested is measured using the method in step (3), and the terahertz characteristic quantity T is calculated and extracted. D and S α Based on the proposed terahertz moisture quantitative evaluation model, the moisture content of the sample to be tested is nondestructively evaluated, and the measurement comparison is based on the GB / T 7600-2014 standard. It is found that the terahertz moisture evaluation method is basically consistent with the standard measurement method, and the error is less than 2ppm. The moisture evaluation results of the sample to be tested are shown in Table 5.

[0117] Table 5 Moisture evaluation results of the tested samples

[0118]

[0119] The embodiment of the present application realizes contactless detection, which is simple and fast, and does not require pretreatment of the sample. While ensuring accuracy, it overcomes the shortcomings of high cost, complexity and time consumption, and poor anti-interference, and can realize non-destructive and rapid detection of the moisture content of transformer insulating oil on site.

[0120] 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.

[0121] 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 detecting moisture content of insulating materials, characterized in that: The insulating material moisture content detection method comprises: Acquire a transmitted terahertz time domain signal to be measured; the transmitted terahertz time domain signal to be measured is a time domain signal after a terahertz wave is emitted to the insulating material to be measured and the terahertz wave is transmitted through the insulating material to be measured; Converting the transmitted terahertz time domain signal to be measured into a frequency domain signal to obtain the transmitted terahertz frequency domain signal to be measured; Extracting features of the transmitted terahertz time domain signal to be measured and the transmitted terahertz frequency domain signal to be measured to obtain terahertz spectrum features of the insulating material to be measured; the terahertz spectrum features include: a time domain signal peak difference and an absorption coefficient integral value; The moisture content of the insulating material to be tested is determined according to the terahertz spectrum characteristics of the insulating material to be tested and a quantitative curve between the terahertz spectrum characteristics and moisture.

2. The method for detecting moisture content of insulating materials according to claim 1, characterized in that: Before determining the moisture content of the insulating material to be tested according to the terahertz spectrum characteristics of the insulating material to be tested and the quantitative curve between the terahertz spectrum characteristics and moisture, the insulating material moisture content detection method further includes: Acquire a standard transmission terahertz time domain signal; the standard transmission terahertz time domain signal comprises: emitting terahertz waves to standard insulating materials with different moisture contents, and a time domain signal after the terahertz waves are transmitted through the standard insulating materials; Converting the standard transmission terahertz time domain signal into a frequency domain signal to obtain a standard transmission terahertz frequency domain signal; Performing feature extraction on the standard transmission terahertz time domain signal and the standard transmission terahertz frequency domain signal to obtain the terahertz spectrum feature of the standard insulating material; According to the terahertz spectrum characteristics and the corresponding real moisture content of the standard insulating material, a statistical model is used to construct a quantitative curve of the terahertz spectrum characteristics and moisture.

3. The method for detecting moisture content of insulating materials according to claim 1, characterized in that: Determining the moisture content of the insulating material to be tested according to the terahertz spectrum characteristics of the insulating material to be tested and the quantitative curve between the terahertz spectrum characteristics and moisture, specifically includes: Normalizing the terahertz spectrum characteristics of the insulating material to be tested to obtain normalized terahertz spectrum characteristics of the insulating material to be tested; The normalized terahertz spectrum characteristics of the insulating material to be tested are substituted into the quantitative curve of the terahertz spectrum characteristics and moisture to obtain the moisture content of the insulating material to be tested.

4. The method for detecting moisture content of insulating materials according to claim 3, characterized in that: The expression of the quantitative curve of terahertz spectrum characteristics and moisture is: Oil_water=a+b*T D +c*S α ; Among them, Oil_water represents the moisture content of the insulating material to be tested; T D represents the normalized peak value difference of the time domain signal; S α represents the normalized integral value of the absorption coefficient; a, b and c are fitting parameters.

5. The method for detecting moisture content of insulating materials according to claim 1, characterized in that: Converting the to-be-measured transmitted terahertz time domain signal into a frequency domain signal to obtain the to-be-measured transmitted terahertz frequency domain signal specifically comprises: The transmitted terahertz time domain signal to be measured is converted into a frequency domain signal by using Fourier transform and Fresnel formula to obtain the transmitted terahertz frequency domain signal to be measured.

6. The method for detecting moisture content of insulating materials according to claim 5, characterized in that: The transmitted terahertz time domain signal to be measured is converted into a frequency domain signal by using Fourier transform and Fresnel formula to obtain the transmitted terahertz frequency domain signal to be measured, specifically comprising: The transmitted terahertz time domain signal to be measured is converted by Fourier transform to obtain a frequency domain amplitude to be measured and a frequency domain phase to be measured; According to the frequency domain amplitude to be measured and the frequency domain phase to be measured, the refractive index and extinction coefficient of the insulating material to be measured are calculated using the Fresnel formula, and the absorption coefficient of the insulating material to be measured is calculated according to the refractive index and extinction coefficient of the insulating material to be measured; the transmitted terahertz frequency domain signal to be measured includes: the absorption coefficient of the insulating material to be measured.

7. The method for detecting moisture content of insulating materials according to claim 1, characterized in that: The time domain signal peak difference is the decrease value of the transmitted terahertz time domain signal compared with the reference time domain signal; the absorption coefficient integral value is the integral value of the absorption spectrum of the transmitted terahertz frequency domain signal within the set spectral range; the reference time domain signal is the time domain signal after the terahertz wave is transmitted through the reference object after emitting a terahertz wave to the reference object; the reference object is air, an empty cuvette, or a cuvette with blank insulating material.

8. The method for detecting moisture content of insulating materials according to claim 2, characterized in that: The actual moisture content is obtained by testing the moisture content of the standard insulating material using the Coulometric method.

9. An insulating material moisture content detection device, characterized in that: The insulating material moisture content detection device comprises: a terahertz transmitter, a cuvette, a terahertz receiver and a processing device; the terahertz transmitter is connected to the processing device; The cuvette is used to hold the insulating material to be tested; the terahertz transmitter is used to transmit terahertz waves to the insulating material to be tested in the cuvette; the terahertz receiver is used to receive the time domain signal after the terahertz wave passes through the insulating material to be tested, and send the obtained transmitted terahertz time domain signal to be tested to the processing device; the processing device is used to execute the insulating material moisture content detection method described in any one of claims 1-8.

10. The device for detecting moisture content of insulating materials according to claim 9, characterized in that: The insulating material moisture content detection device further comprises: a first reflector, a first focusing lens, a second reflector and a second focusing lens; The first reflector is arranged on the output light path of the terahertz transmitter; the first focusing lens is arranged on the reflected light path of the first reflector; the cuvette is arranged on the transmitted light path of the first focusing lens; the second focusing lens is arranged on the output light path of the cuvette; the second reflector is arranged on the transmitted light path of the second focusing lens; and the terahertz receiver is arranged on the reflected light path of the second reflecting lens.

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