CN108680613B - Method for evaluating moisture content in insulating paper by using initial slope of complex dielectric constant - Google Patents
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Abstract
A method for evaluating the water content in insulating paper by using the initial slope of complex dielectric constant features that the real part of complex dielectric constant is 10-f‑4And the absolute value | k | of the change rate at Hz is used as a frequency domain characteristic parameter for representing the moisture degree of the oilpaper. The experimental study has studied the change law of compound dielectric constant and | k | of the insulating sample of oiled paper of different moisture content, and the research result shows: along with the rising of the moisture content M of the insulating paper, the complex dielectric constant real part 'curve of the oilpaper test sample is in a trend of translating towards a high frequency band, the change amplitude of the complex dielectric constant real part of the low frequency band is increased along with the rising of the moisture content, and through actual measurement and fitting of a' -f curve, a better exponential function relation is found between the k | and the oilpaper moisture content M, so that the method can be used for quantitatively evaluating the insulation moisture degree of the oilpaper.
Description
Technical Field
The invention relates to the field of insulation state diagnosis and detection and service life evaluation of oil paper insulation power equipment, in particular to a method for evaluating moisture content in insulation paper by using an initial slope of a complex dielectric constant.
Background
The oil-immersed transformer is used as a core device in a power system, and the operation state of the oil-immersed transformer is related to the balance and stability of the whole power grid, so that the safety operation of the transformer is very important. The oil paper insulation is used as a main structure of the oil-immersed transformer inner insulation, wherein the moisture degree of the insulation paper is closely related to the performance of the oil paper insulation, and researches show that the increase of the moisture content can promote the thermal aging process of the insulation paper, and the insulation paper can be gradually cracked to generate moisture and absorb the moisture from the air in the thermal aging process, so that the thermal aging cracking process of the insulation paper is accelerated, the oil paper insulation performance is more and more poor, and the service life of the insulation paper is rapidly reduced. Therefore, quantitative evaluation of the moisture content of the oiled paper insulation is very important. The traditional method for detecting the moisture content in the insulating paper is easy to damage an insulating structure in the sampling process, and the test result is inaccurate due to the unbalanced distribution of the moisture among the paperboards. The Frequency Domain Spectroscopy (FDS) is used as a nondestructive electrical measurement technology, can effectively obtain the data of the oil-paper insulation complex dielectric constant changing along with the Frequency, has strong anti-jamming capability, and is more suitable for field diagnosis and evaluation of the insulation state of the oil-immersed transformer.
The dielectric constant is the response of a medium to an electric field under an applied electric field, the real part of the dielectric constant represents the macroscopic polarization degree and can effectively reflect the magnitude and the change state of the polarization intensity, the dielectric response of the dielectric to the applied electric field depends on the frequency of the electric field to a great extent, and when the frequency of the applied electric field is higher, the polarization relaxation process does not occur instantaneously but is delayed to be established, so a certain phase difference exists between the dielectric response and the applied electric field, and therefore, the dielectric constant (omega) is a complex function of the frequency of the applied electric field: and the real part of the complex dielectric constant (omega) represents the magnitude of the polarization intensity, and the imaginary part (omega) reflects various steering polarization in the material at high frequency and various relaxation polarization losses caused by the fact that the high-frequency electric field change cannot be followed by various steering polarization. At present, domestic and foreign scholars develop research on quantitative relation between frequency domain characteristic quantity of complex dielectric constant and the insulation moisture degree of the oil paper based on FDS test technology, and the result shows that the increase of moisture content can cause the change of polarization and relaxation processes in the insulation, so that the change of the insulation complex dielectric constant of the oil paper is monitored, the change rules of a real part and an imaginary part of the oil paper are respectively researched, and the change of the insulation state of the oil paper can be more effectively analyzed.
Disclosure of Invention
Aiming at the technical problems, the method aims to more accurately evaluate the insulation moisture state of the transformer oilpaper by utilizing the frequency domain dielectric characteristic quantityThe invention provides a method for evaluating the moisture content in insulating paper by using the initial slope of a complex dielectric constant, wherein the real part of the complex dielectric constant is 10-f-4And the absolute value | k | of the change rate in Hz is used as a frequency domain characteristic parameter for representing the degree of wetting of the oil paper. The experimental study has studied the change law of compound dielectric constant and | k | of the insulating sample of oiled paper of different moisture content, and the research result shows: along with the increase of the moisture content M of the insulating paper, the complex dielectric constant real part 'curve of the oilpaper test sample is in a trend of translating towards a high frequency band, the change amplitude of the complex dielectric constant real part of the low frequency band is increased along with the increase of the moisture content, and through actual measurement and' f curve fitting, a better exponential function relation is found between the k | and the moisture content M of the oilpaper, so that the method can be used for quantitatively evaluating the insulation moisture degree of the oilpaper. The method has the characteristics of simpler operation and no damage to the internal insulation structure of the transformer, and is more suitable for the evaluation of the insulation moisture state of the transformer.
The technical scheme adopted by the invention is as follows:
a method for evaluating the moisture content in insulating paper by using the initial slope of complex dielectric constant comprises the following steps:
step 1: defining the real part of the complex dielectric constant as the frequency variation curve at the frequency point f as 10-4Initial rate of change k in HzcIs the initial slope of the real part of the complex permittivity, by kcPredicting the moisture degree of insulating paper in the oil-immersed transformer;
step 2: the method comprises the steps of simulating an internal insulation structure of the oil-immersed transformer by adopting a three-electrode device, recording structural parameters, obtaining complex capacitance parameters of insulation paper by a frequency domain dielectric spectrum measuring instrument, obtaining a change curve of a complex dielectric constant real part 'along with frequency by a calculation formula of the capacitance parameters, the dielectric constant and the insulation structure, and calculating the change curve of the complex dielectric constant real part' along with the frequency at a frequency point f of 10-4Absolute value of initial rate of change in Hzc|；
And step 3: five groups of insulation paper samples with different water contents are prepared in a laboratory through a natural moisture absorption method, and the absolute value | k of the initial change rate of the real part' of the complex dielectric constant is measured and calculatedcAnalysis of | kcThe quantitative relation between the moisture degree of the insulating paper and the moisture degree of the insulating paper;
and 4, step 4: data fitting | kcObtaining an exponential fitting relation function expression of | and the moisture content M of the insulating paper, wherein the function relation expression is | kc21770 exp (0.4372M), which explains the absolute value of the initial rate of change | kcThe smaller the | is, the smaller the water content in the insulating paper is, the better the insulation degree in the transformer is, and the | k can be utilizedcAnd quantitatively evaluating the water content of the transformer insulation paper.
In step 1, a test frequency f is defined as 10-4At Hz,' the absolute value of the initial rate of change is | kcInitial slope | kcD'/df due to | kcThe value range of | is in a low frequency band, the value of | depends on the establishment process of the rapid polarization in the insulating oil paper, and the polarization relaxation process in the dielectric is closely related to the content of water molecules in the dielectric, so that | k can be obtainedcAnd l, evaluating the moisture degree of the oil paper insulation of the transformer.
In the step 1, a frequency domain dielectric spectrum curve of the real part of the complex dielectric constant is provided at a frequency point f to 10-4Initial rate of change k in HzcPerforming frequency domain dielectric spectrum test on the insulating oilpaper sample to obtain the first 7 measured data points of the frequency domain spectrum curve of the real part of the complex dielectric constant, obtaining a linear relation of the first 7 data points through curve fitting, and then changing the frequency f to 10-4Substituting Hz to obtain the initial change rate kc，kcThe method reflects the establishment process of the rapid polarization in the insulating oil paper, and the polarization establishment process mainly depends on the content of water molecules in the oil paper insulating medium and can be used for evaluating the moisture state of the oil paper insulating whole body of the oil-immersed transformer. In the step 2, a three-electrode device is used for simulating an internal insulation structure of the oil-immersed transformer in a laboratory, and measurement is performed at room temperature (about 30 ℃); in the preparation process of the insulating paper moisture test sample, the experimental materials adopt a cellulose kraft insulating paper wafer with the thickness of about 0.5mm and the radius of 65mm and 25# American high transformer insulating oil, the dried insulating paper is exposed in the air to absorb moisture naturally, a precision electronic scale is used for weighing once every half hour, the moisture content M is respectively 0.7 percent, 1.3 percent and 2.5 percent by calculating the mass of the insulating paper wafer before and after moisture absorption,3.4 percent of insulating paper sample and 4.2 percent of insulating paper sample, wherein each group of insulating paper sample is formed by overlapping five insulating paper wafers.
In the step 2, the measuring instrument selects an IDAX-300 dielectric response tester produced by Megger company of America, the testing is carried out at room temperature, in the preparation process of the insulation paper moisture test sample, the test materials adopt a cellulose kraft insulation paper wafer with the thickness of about 0.5mm and the radius of 65mm and 25# American high transformer insulation oil, the dried insulation paper is exposed in the air to absorb moisture naturally, weighing is carried out once by a precision electronic scale every half hour, five groups of insulation paper test samples with the moisture content M of 0.7%, 1.3%, 2.5%, 3.4% and 4.2% are prepared by calculating the mass of the insulation paper wafer before and after moisture absorption, and each group of test samples are formed by overlapping five insulation paper wafers;
the method for setting the parameters of the test equipment comprises the following steps: setting the maximum value U of the AC supply voltagemax200V, highest test frequency fH4kHz, lowest test frequency fLData measurements can be made at 0.1 mHz. Wherein U ismaxThe method is a universal set value when the dielectric spectrum of the oilpaper insulation frequency domain is tested, and the test frequency band is selected to be 0.1 mHz-4 kHz, so that the measurement range is wider, the obtained information is richer, and the measurement result is more reliable.
In the step 3, because the oiled paper insulation is a conventional dielectric medium, the alternating voltage applied to the oiled paper insulation causes a polarization relaxation phenomenon to occur inside the oiled paper insulation, when polar molecules inside the medium increase, the polarization intensity increases, the dielectric constant increases inevitably, and both slow polarization and fast polarization in a low frequency band can have enough time to be established. However, after the oil paper is insulated and damped, the number of water molecules is increased sharply, and because the internal polarization is mostly caused by moisture and belongs to a rapid polarization process, the initial change rate of the complex dielectric constant of the oil paper is strongly influenced by the moisture polarization, so that the reduction rate is faster. The analysis shows that the change of the moisture content has obvious influence on the real part of the complex dielectric constant, and the experimental data and the result analysis are compared to obtain the moisture content M and the moisture content kcThe functional relationship between the two is:
|kc|＝2.177×104·exp(0.4372M)
k for insulating actual measurement transformer oilpapercSubstituting the formula to obtain the value of M, thereby preliminarily predicting and evaluating the moisture state of the oil paper insulation.
The invention relates to a method for evaluating the moisture content in insulating paper by using the initial slope of complex dielectric constant, which has the following technical effects:
1. the moisture state of the paper insulation in the oil paper insulation can be analyzed on the premise of not hanging the core, not damaging the insulation material and not sampling, and a reliable basis is provided for accurately evaluating the insulation performance of the oil paper insulation power equipment.
2. The initial slope | kc | of the complex dielectric constant provided by the invention can effectively and reliably evaluate the insulation moisture degree of the internal paper of the transformer, is simpler and more convenient to operate, does not damage the insulation structure of equipment, and is a better diagnosis method for the insulation moisture state of the transformer.
Drawings
FIG. 1 is a schematic flow chart of the operation of the present invention.
FIG. 2 is a measured frequency spectrum of the real part of the complex permittivity.
FIG. 3 is a schematic view of a three-electrode device;
in fig. 3: 1-measuring electrode, 2-high voltage electrode, 3-protective electrode, 4-transformer oil and 5-insulating paper sample.
FIG. 4 shows the absolute values of M and the initial slope values | k of real parts of complex dielectric constants of different water samplescFitted graph of | s.
Detailed Description
Principle analysis:
a method for evaluating the moisture content in insulating paper by using the initial slope of a complex dielectric constant is combined with experiments and theories to research the influence rule and the numerical value relation between the absolute value of the initial slope of a frequency domain dielectric spectrum curve of the real part of the complex dielectric constant and the moisture content of the paper in oil paper insulation. The alternating voltage applied on the dielectric medium causes polarization relaxation phenomenon to occur in the dielectric medium, when polar molecules in the dielectric medium increase, the polarization intensity increases, the increase of the dielectric constant is inevitable, and the slow polarization and the fast polarization in the low frequency band can have enough time to establishAnd (5) standing. However, after insulation is affected with damp, the quantity of water molecules is increased sharply, because internal polarization is mostly caused by moisture and belongs to a rapid polarization process, the initial change rate of the insulation complex dielectric constant of the oilpaper is strongly influenced by moisture polarization, so that the' descending speed is faster, the water molecules are used as strong polar molecules, the polarization strength of the whole oilpaper is enhanced due to the increase of the quantity of the water molecules, and the | k iscI is the initial value of the rate of change of the real part of the complex permittivity, i.e. the rate of change of the polarization instant ', which is mainly influenced by the rapid polarization process, i.e. the influence of water molecules on the polarization of the dipoles, so that the initial value of the rate of change i k is the initial value of the ' rate of change ' with increasing moisture contentcThe | will gradually increase. Obtaining the | k of the oiled paper samples under different water contents M through fittingcAnd the functional relation between the I and the M can be used for quantitatively evaluating the insulation moisture degree of the oil paper.
A method for evaluating the moisture content in insulating paper by using the initial slope of complex dielectric constant comprises the following steps:
1) defining the real part of the complex dielectric constant as the frequency variation curve at the frequency point f as 10-4Initial rate of change k in HzcIs the initial slope of the real part of the complex permittivity, by kcPredicting the moisture degree of insulating paper in the oil-immersed transformer; verified by experiments, kcThe moisture content M has obvious gradient relation with the moisture content M of the paper insulation in the transformer oil paper insulation, and the moisture content M is closely related to the moisture degree of the oil paper insulation, so that the moisture degree of the oil paper insulation of the transformer can be evaluated.
2) The internal insulation structure of the oil-immersed transformer is simulated by adopting the three-electrode device, structural parameters are recorded, the complex capacitance parameters of the insulation paper are obtained through the frequency domain dielectric spectrum measuring instrument, the change curve of the real part of the complex dielectric constant along with the frequency is obtained through the calculation formula of the capacitance parameters, the dielectric constant and the insulation structure, and the change curve is calculated to be 10 at the frequency point f-4Absolute value of initial rate of change in Hzc|；
3) Preparing five groups of insulation paper samples with different water contents by a natural moisture absorption method in a laboratory, measuring and calculating an absolute value | k of an initial change rate of a real part' of a complex dielectric constantcAnalysis of | kcI and ZhiQuantitative relation between the moisture degrees of the margin paper; according to the analysis of experimental data results, the polarization relaxation phenomenon occurs in the dielectric medium due to the alternating voltage applied to the dielectric medium, when polar molecules in the dielectric medium are increased and the polarization intensity is increased, the increase of the dielectric constant is inevitably caused, and the slow polarization and the fast polarization in the low frequency band can be established for enough time. However, after insulation is affected with damp, the quantity of water molecules is increased sharply, because internal polarization is mostly caused by moisture and belongs to a rapid polarization process, the initial change rate of the insulation complex dielectric constant of the oilpaper is strongly influenced by moisture polarization, so that the' descending speed is faster, the water molecules are used as strong polar molecules, the polarization strength of the whole oilpaper is enhanced due to the increase of the quantity of the water molecules, and the | k iscI is the initial value of the rate of change of the real part of the complex permittivity, i.e. the rate of change of the polarization instant ', which is mainly influenced by the rapid polarization process, i.e. the influence of water molecules on the polarization of the dipoles, so that the initial value of the rate of change i k is the initial value of the ' rate of change ' with increasing moisture contentcThe | will gradually increase. Obtaining the | k of the oiled paper samples under different water contents M through data fittingcFunctional relationship | k between | and McAnd (3) 21770 exp (0.4372M), namely the moisture content of the oiled paper insulation can be quantitatively evaluated.
As shown in fig. 2, the measured frequency spectrum of the real part of the complex permittivity of the present invention is represented by 'the real part of the complex permittivity', f is the frequency, and M is the moisture content in the insulating paper. Each dielectric line is 10 at f-4The absolute value of the slope d'/df at Hz is the initial slope | kc|。
Preparing a moisture test sample: in order to facilitate the determination of the moisture content of the samples, firstly, fully drying each group of sample insulation paper, weighing to obtain the gross weight of each group of samples, then exposing the samples to the air (at room temperature) for natural moisture absorption, weighing once by using a precision electronic scale every half hour, dividing the weight increased after moisture absorption by the mass after moisture absorption to obtain the moisture content of the samples, and performing FDS test after the moisture content of the samples is recorded.
An experiment platform is built: simulation of internal insulation of oil-immersed transformer using three-electrode deviceThe structure of the device, as shown in FIG. 3, is IDAX-300 dielectric response tester manufactured by Megger corporation, USA, for measuring voltage peak value Umax200V, maximum test frequency fH4kHz, lowest test frequency fL0.1 mHz. In order to prevent the interference of the external temperature, the experiment is carried out in a 30 ℃ thermostat, and before the test is started, the sample is allowed to stand in the thermostat for 6 hours so as to be fully preheated and ensure that the whole test sample reaches 30 ℃.
FIG. 4 is a fitting curve of the absolute value of the initial slope of the real part of the complex dielectric constant of the oil paper insulation system and M under different M measured in the present invention, and it can be seen from the figure that the rising of the moisture content M in the insulation paper drives the absolute value of the initial slope | kcL is increased at the same time.
Because the quantity of water molecules is greatly increased, the internal polarization is mostly caused by moisture and belongs to a rapid polarization process, the initial change rate of the complex dielectric constant of the oilpaper insulation is strongly influenced by the moisture polarization, so that the dropping rate is faster, and the absolute value | k of the initial slope of the complex dielectric constantcI also increases, and its relationship to M is discussed below.
The initial slope and the moisture content have the following functional relationship:
|kc|＝2.177×104·exp(0.4372M)；
wherein, | kcI is the absolute value of the initial slope of the frequency domain dielectric spectrum curve of the real part of the complex dielectric constant, and M is the moisture content (percent) of the paper insulation in the oiled paper insulation structure;
in conclusion, fitting curves and | k | of the initial FDS sections of the moisture samples' with different M are obtained, as shown in the following table 1:
as can be seen from the data in Table 1 above, | kcThe | is gradually increased along with the increase of the water content M, because the water molecule is a strong polar molecule, the polarization intensity of the whole oilpaper is enhanced due to the | k |, due to the increase of the number of the water moleculesc| is the rate of change of the real part of the complex permittivityThe initial value, i.e. the rate of change of the polarization instant', which is mainly influenced by the fast polarization process, i.e. the influence of water molecules on the polarization of the dipoles, so that with increasing moisture content the initial value of the rate of change i kcAnd | gradually increases.
The real part and the imaginary part of the relative dielectric constant of the oiled paper insulation sample are very sensitive to the moisture content of the insulating paperboard, the 'AND' gradually increases along with the increase of the moisture content, the '-f curve tends to move in a high frequency band, and the real part' of the complex dielectric constant is 10-fold at f4～10-2The falling amplitude in the Hz band is gradually increased.
The invention adopts the FDS curve of the real part of the complex dielectric constant at f ═ 10-4Absolute value of slope | k in HzcI is used as a frequency domain characteristic parameter for quantitatively evaluating the insulation moisture degree of the oil paper, and the I k is obtained through fitting calculation of an actually measured' -f curvecThe value has a good exponential function relation with M, and another set of experiments verify that the characteristic parameter | k provided by the inventioncThe effectiveness of | k in evaluating the moisture degree of the oil paper insulation can becThe method is used for field detection of the transformer oilpaper insulation moisture degree. The research result of the invention provides a new research idea for further providing the diagnosis of the insulation moisture state by utilizing the initial slope characteristic quantity.
Claims (6)
1. A method for evaluating the moisture content in insulating paper by using the initial slope of complex dielectric constant is characterized by comprising the following steps:
step 1: defining the real part of the complex dielectric constant as the frequency variation curve at the frequency point f as 10-4Initial rate of change k in HzcIs the initial slope of the real part of the complex permittivity, by kcPredicting the moisture degree of insulating paper in the oil-immersed transformer;
step 2: the method comprises the steps of simulating an internal insulation structure of the oil-immersed transformer by adopting a three-electrode device, recording structural parameters, obtaining complex capacitance parameters of insulation paper through a frequency domain dielectric spectrum measuring instrument, obtaining a change curve of a complex dielectric constant real part 'along with frequency through a calculation formula of the capacitance parameters, the dielectric constant and the insulation structure, and calculating the change curve of the complex dielectric constant real part' along with the frequency at a frequency pointf＝10-4Absolute value of initial rate of change in Hzc|；
And step 3: five groups of insulation paper samples with different water contents are prepared in a laboratory through a natural moisture absorption method, and the absolute value | k of the initial change rate of the real part' of the complex dielectric constant is measured and calculatedcAnalysis of | kcThe quantitative relation between the moisture degree of the insulating paper and the moisture degree of the insulating paper;
and 4, step 4: data fitting | kcObtaining an exponential fitting relation function expression of | and the moisture content M of the insulating paper, wherein the function relation expression is | kc21770 exp (0.4372M), which explains the absolute value of the initial rate of change | kcThe smaller the | is, the smaller the water content in the insulating paper is, the better the insulation degree in the transformer is, and the | k is usedcAnd quantitatively evaluating the water content of the transformer insulation paper.
2. The method for estimating the moisture content in the insulating paper by using the initial slope of the complex dielectric constant as claimed in claim 1, wherein: in step 1, a test frequency f is defined as 10-4At Hz,' the absolute value of the initial rate of change is | kcInitial slope | kcD'/df due to | kcThe value range of | is in a low frequency band, the value of | depends on the establishment process of the rapid polarization in the insulating oil paper, and the polarization relaxation process in the dielectric is closely related to the content of water molecules in the dielectric, so that | k is obtainedcAnd l, evaluating the moisture degree of the oil paper insulation of the transformer.
3. The method for estimating the moisture content in the insulating paper by using the initial slope of the complex dielectric constant as claimed in claim 1, wherein: in the step 1, a frequency domain dielectric spectrum curve of the real part of the complex dielectric constant is provided at a frequency point f to 10-4Initial rate of change k in HzcPerforming frequency domain dielectric spectrum test on the insulating oil paper sample to obtain the first 7 measured data points of the frequency domain spectrum curve of the real part of the complex dielectric constant, obtaining a linear relation of the first 7 data points through curve fitting, and then setting the frequency f to be 10-4Substituting Hz to obtain the initial change rate kc，kcReflects the insulating oilpaperThe method is characterized by comprising an internal rapid polarization establishing process, wherein the polarization establishing process mainly depends on the content of water molecules in an oil paper insulating medium, and can be used for evaluating the moisture state of the oil paper insulating whole body of the oil-immersed transformer.
4. The method for estimating the moisture content in the insulating paper by using the initial slope of the complex dielectric constant as claimed in claim 1, wherein: in the step 2, a three-electrode device is used for simulating an internal insulation structure of the oil-immersed transformer in a laboratory, and measurement is carried out at room temperature; in the preparation process of the insulating paper moisture test sample, the experimental materials adopt a cellulose kraft insulating paper wafer with the thickness of 0.5mm and the radius of 65mm and 25# American high transformer insulating oil, the dried insulating paper is exposed in the air to absorb moisture naturally, a precision electronic scale is used for weighing once every half hour, five groups of insulating paper test samples with the moisture contents M of 0.7%, 1.3%, 2.5%, 3.4% and 4.2% are prepared by calculating the mass of the insulating paper wafer before and after moisture absorption, and each group of test samples are formed by overlapping five insulating paper wafers.
5. The method for estimating the moisture content in the insulating paper by using the initial slope of the complex dielectric constant as claimed in claim 1, wherein: in the step 2, the measuring instrument selects an IDAX-300 dielectric response tester produced by Megger company of America, the testing is carried out at room temperature, in the preparation process of the insulation paper moisture test sample, the test materials adopt a cellulose kraft insulation paper wafer with the thickness of about 0.5mm and the radius of 65mm and 25# American high transformer insulation oil, the dried insulation paper is exposed in the air to absorb moisture naturally, weighing is carried out once by a precision electronic scale every half hour, five groups of insulation paper test samples with the moisture content M of 0.7%, 1.3%, 2.5%, 3.4% and 4.2% are prepared by calculating the mass of the insulation paper wafer before and after moisture absorption, and each group of test samples are formed by overlapping five insulation paper wafers;
the method for setting the parameters of the test equipment comprises the following steps: setting the maximum value U of the AC supply voltagemax200V, highest test frequency fH4kHz, lowest test frequency fLData measurements were taken at 0.1 mHz.
6. The method for estimating the moisture content in the insulating paper by using the initial slope of the complex dielectric constant as claimed in claim 1, wherein: in the step 4, the water contents M and kcThe functional relationship between the two is:
|kc|＝2.177×104·exp(0.4372M)
k for insulating actual measurement transformer oilpapercSubstituting the formula to obtain the value of M, thereby preliminarily predicting and evaluating the moisture state of the oil paper insulation.
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