CN111812467A - Method for evaluating aging state of oil-impregnated transformer oil paper insulation system - Google Patents
Method for evaluating aging state of oil-impregnated transformer oil paper insulation system Download PDFInfo
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- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
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Abstract
The invention relates to a method for evaluating the aging state of an oil-impregnated transformer oil paper insulation system, which belongs to the field of power equipment evaluation and comprises the following steps: s1: carrying out frequency domain dielectric response test on oil-immersed insulating paper boards with different moisture contents and aging states; s2: extracting dielectric modulus characteristic quantity representing synergistic influence of the moisture and the aging product; s3: and constructing the correlation between the polymerization degree of the oil-immersed insulating paperboard and the imaginary part integral value of the dielectric modulus under the synergistic effect of the moisture and the aging product. The method can be used for evaluating the aging state of the oil paper insulation system of the oil-immersed power transformer by fusing the synergistic effect of the moisture and the aging product, the moisture content range can be in the range of 0.5-5%, the method is more suitable for the operation practice of the oil-immersed transformer on site, and the technical problem that the evaluation of the aging state of the oil paper insulation system is inaccurate by only considering a single factor (moisture or aging) in the traditional method is solved.
Description
Technical Field
The invention belongs to the field of power equipment evaluation, and relates to a method for evaluating the aging state of an oil-paper insulation system of an oil-immersed transformer.
Background
Power transformers are the core power devices for power transfer and energy conversion in power systems. In 110kV and above voltage level electric network, the oil-immersed power transformer is widely applied. In the actual operation process, the oil-paper insulation system (insulating oil, cellulose insulation material) inside the oil-immersed power transformer is gradually deteriorated under the influence of electrical stress, thermal stress, mechanical stress, environmental factors and the like, so that the mechanical strength of the oil-paper insulation system is reduced, and the moisture, acidic products and the like are gradually increased. The insulation aging of the oil paper is easy to cause the reduction of the insulation performance of the power transformer, even induce the insulation failure, and seriously threaten the safe and stable operation of the transformer and the power system. Therefore, the aging state of the transformer oil paper insulation system is effectively evaluated, and the method has great significance for ensuring safe and stable operation of the transformer.
The aging state of oil-filled power transformers is mainly dependent on the aging state of the solid cellulose insulation paper (board). At present, researchers at home and abroad carry out a great deal of research on the evaluation of the damp or aging state of the oil-immersed cellulose insulating paperboard. Commonly used diagnostic methods are classified into a physicochemical diagnostic method and an electrical diagnostic method, wherein the physicochemical diagnostic method includes a dissolved gas in oil method, a furfural content method, an acid value method, a micro-water content method, and the like; the electric diagnosis method comprises a power frequency dielectric loss method, a polarization depolarization current method, a return voltage method, a frequency domain dielectric spectroscopy method and the like. However, the solid insulating material in the oil paper insulating system of the oil-immersed transformer is not easy to replace, and the method for diagnosing the aging state by adopting the chemical parameters in the oil is easily influenced by oil replacement, so that the evaluation result is inaccurate, and the aging state evaluation cannot be directly completed by measurement on site; the power frequency dielectric loss method is insensitive to insulation deterioration; the polarization depolarization current method and the return voltage method are susceptible to external electromagnetic noise interference. Compared with the method, the frequency domain dielectric spectrum method has the advantages of no loss, wide frequency band, strong anti-interference capability and rich insulation state information contained in the measurement result, and is widely applied to insulation state diagnosis and aging state evaluation of power equipment.
Researchers at home and abroad use the frequency domain dielectric spectroscopy technology to carry out a lot of researches on the insulation aging state and the moisture state of the oil-immersed power transformer. The influence of moisture on the frequency domain dielectric property of an oil paper insulation sample is analyzed by Dag Linhjell and the like of Norwegian scholars, and the fact that the real part and the imaginary part of the complex dielectric constant gradually move towards the high-frequency direction along with the increase of the moisture content shows that a loss peak appears in a complex dielectric constant imaginary part curve under the condition of higher moisture content. Lundgaard and the like perform frequency domain dielectric spectrum tests on three oil paper insulation samples with different moisture degrees, and the results show that the low-frequency part of the complex phase dielectric constant of the samples is gradually increased along with the increase of the moisture degree, and the high-frequency area is basically not influenced. Poovamma et al, indian scholars, studied the effect of aging on the frequency domain dielectric spectrum FDS of oiled paper insulation samples, and showed that the imaginary part of the relative dielectric constant and the dielectric loss of the samples gradually increased as the aging degree increased. Frequency domain dielectric spectrum FDS tests are carried out on the oiled paper insulation samples in different thermal ageing states by Haokou construction and the like at Chongqing university in China, and the results show that the influence of the oiled paper insulation ageing on the low-frequency area of the frequency domain dielectric spectrum is obvious, the dielectric constant and the dielectric loss at the characteristic frequency of the low-frequency area and the polymerization degree follow an exponential function relationship, and the polymerization degree is gradually reduced along with the increase of the dielectric constant and the dielectric loss. Research such as Liao Rui of Chongqing university analyzes the influence of moisture and aging on dielectric properties of an oil paper insulation frequency domain, shows that the influence frequency bands of the moisture and the aging on a dielectric loss curve are different, and characteristic quantities are obtained by integrating the dielectric loss curves of different frequency bands to distinguish the influence of the moisture and the aging. The frequency domain dielectric test is carried out on oil-immersed insulating paper boards with different moisture contents by Liujifeng and the like in Guangxi university, and the influence of moisture is quantified by extracting characteristic quantity of a medium loss integral value through a frequency domain dielectric curve.
At present, scholars at home and abroad mainly study the influence of single influence factor moisture or aging on the dielectric property of the oiled paper insulating medium or distinguish the influence frequency bands of the moisture and aging on a frequency domain dielectric curve. In addition, the existing methods for evaluating the aging state of the transformer oil paper insulation system are all obtained under the condition that the moisture content of the oil paper insulation system is basically kept constant (< 1%), and the moisture content of the transformer oil paper insulation system is gradually increased along with the increase of the operation age of the transformer oil paper insulation system, so that the existing methods are not completely suitable for evaluating the aging state of the transformer oil paper insulation system when the moisture content is higher than 1%, and the evaluation error is large. Therefore, to accurately evaluate the aging state of the oil paper insulation of the transformer, the influence of moisture and aging products on the frequency domain dielectric of the oil paper insulation system needs to be comprehensively considered.
Disclosure of Invention
In view of the above, the invention aims to provide a method for evaluating the aging state of an oil-impregnated power transformer oil-paper insulation system by applying a frequency domain dielectric modulus imaginary part integral value, which is suitable for the field of oil-impregnated power equipment oil-paper insulation aging state evaluation by fusing the synergistic effect of moisture and an aging product to evaluate the aging state of the oil-impregnated power transformer oil-paper insulation system.
In order to achieve the purpose, the invention provides the following technical scheme:
a method for evaluating the aging state of an oil-impregnated transformer oil paper insulation system comprises the following steps:
s1: carrying out frequency domain dielectric response test on oil-immersed insulating paper boards with different moisture contents and aging states;
s2: extracting dielectric modulus characteristic quantity representing synergistic influence of the moisture and the aging product;
s3: and constructing the correlation between the polymerization degree of the oil-immersed insulating paperboard and the imaginary part integral value of the dielectric modulus under the synergistic effect of the moisture and the aging product.
Further, step S1 specifically includes the following steps:
s11: carrying out accelerated thermal aging on the oil-immersed insulating paper board in a thermal aging box at 120 ℃, and then carrying out moisture absorption tests on the oil-immersed insulating paper board in an unaged state and different thermal aging states to obtain oil-immersed insulating paper boards with different moisture contents and aging states;
s12: and carrying out frequency domain dielectric characteristic test on the oil-immersed insulating paper boards containing different moisture contents and aging states to obtain frequency domain dielectric spectrums of the oil-immersed insulating paper boards containing different moisture contents and aging states.
Further, step S2 specifically includes the following steps:
s21: converting the frequency domain dielectric curve of the oil-immersed insulating paperboard affected by the synergistic effect of moisture and aging into a dielectric modulus spectrum curve by adopting a formula (1):
where M' (ω) and M "(ω) represent the real and imaginary parts of the dielectric modulus, respectively. ' (ω) and "(ω) represent the real and imaginary parts of the complex permittivity in the frequency domain, respectively.
S22: comprehensively considering the synergistic effect of moisture and aging on the oil-immersed insulating paperboard, integrating the imaginary part of the dielectric modulus by adopting a formula (2), wherein the integral value is called a modulus factor A(DP-mc％)And quantifying and characterizing the synergistic effect of moisture and aging on the oil-immersed insulating paperboard:
where M "(f) represents the imaginary part of the dielectric modulus and f represents the test frequency.
Further, step S3 specifically includes:
s31: aiming at oil-immersed insulating paper boards in different aging states, constructing a function relation between a modulus factor and moisture;
s32: adopting a 'polymerization degree-water' translation idea, selecting a modulus factor curve with a specific polymerization degree as a reference curve, and moving the modulus factor curves with the other polymerization degrees to the reference curve along the horizontal direction to form a main curve;
s33: fitting the main curve with a non-linear function using equation (3):
wherein a, b and c are fitting coefficients of a nonlinear function, mc%refMoisture content under the main curve;
s34: the ratio of the water content before curve translation to the water content after translation is referred to as the translation factor psi of degree of polymerizationDPDegree of polymerization translation factor psiDPThe calculation formula is as follows:
in the formula, (mc%)DPIs the moisture content before curve translation, (mc%) ref is the moisture content after curve translation;
s35: constructing polymerization degree translation factor psi according to Allen's equation formDPAnd (1/DP)ref-1/DP) as follows:
wherein DPrefIs the degree of polymerization corresponding to the reference curve, DP is the degree of polymerization corresponding to the translated curve, EDPIs a constant related to the degree of polymerization of the oil-immersed insulating paperboard;
obtaining formula (6) by simultaneously taking logarithm of two sides of equal sign of formula (5), and further constructing psiDPAnd (1/DP)ref-1/DP):
s36: for ln psiDPAnd (1/DP)ref-1/DP) is fitted, the fitting formula is as follows:
s37: obtaining a formula for evaluating the aging state of the oil-immersed insulating paperboard by fusing the synergistic effect of the moisture and the aging product:
thereby deducing the polymerization degree of the insulating paperboard under the synergistic effect of the fused moisture and the aging product:
the invention has the beneficial effects that: the method can be used for evaluating the aging state of the oil paper insulation system of the oil-immersed power transformer by fusing the synergistic effect of the moisture and the aging product, the moisture content range can be in the range of 0.5-5%, the method is more suitable for the operation practice of the oil-immersed transformer on site, and the technical problem that the evaluation of the aging state of the oil paper insulation system is inaccurate by only considering a single factor (moisture or aging) in the traditional method is solved.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.
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For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic diagram of a frequency domain dielectric spectroscopy test system;
FIG. 2 is a frequency domain dielectric spectrum of 832-degree-of-polymerization oil-immersed insulating paper board with different water contents;
FIG. 3 is a dielectric modulus spectrum of 832-degree-of-polymerization oil-impregnated insulating paper boards with different moisture contents;
FIG. 4 is a graph of modulus factors of oil-impregnated insulating paper boards of different moisture contents and aging states;
FIG. 5 is a graph showing the relationship between modulus factor and moisture content at different degrees of polymerization;
FIG. 6 is a process diagram of constructing a main curve for synergistic effect of fusion moisture and aging, FIG. 6(a) is a translation process diagram, and FIG. 6(b) is a main curve diagram;
FIG. 7 shows ln ψDPAnd (1/DP)ref-1/DP);
FIG. 8(a) is a frequency domain dielectric spectrum of a validated laboratory oil paper cellulose paperboard, and FIG. 8(b) is a dielectric modulus spectrum;
FIG. 9(a) shows the complex capacitance of the main insulation of the power transformer measured actually, and FIG. 9(b) shows the complex dielectric constant;
FIG. 10 is an equivalent model of a main insulation structure of a transformer, FIG. 10(a) is the main insulation structure, and FIG. 10(b) is the equivalent XY model;
fig. 11(a) is a complex dielectric constant spectrum of an oil-immersed insulating paper board in main insulation of a transformer, and fig. 11(b) is a dielectric modulus spectrum;
FIG. 12 is a flowchart illustrating the process of evaluating the aging status of the oil-impregnated paper board and the oil-impregnated transformer oil-impregnated paper insulation system;
FIG. 13 is a flow chart of an implementation of the present invention.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.
Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.
The invention provides a method for evaluating the aging state of an oil-impregnated power transformer oil-paper insulation system by applying a frequency domain dielectric modulus imaginary part integral value, which can be used for evaluating the aging state of the oil-impregnated power transformer oil-paper insulation system by fusing the synergistic effect of moisture and an aging product, wherein the moisture content range can be 0.5-5%, the method is more suitable for the operation practice of an on-site oil-impregnated power transformer, and the technical problem that the aging state of the oil-paper insulation system is not accurately evaluated by only considering a single factor (moisture or aging) in the traditional method is solved.
The embodiment comprises the following steps:
1. frequency domain dielectric response test of aged oil-immersed insulating paper board containing different moisture contents
Firstly, the oil-immersed insulating paperboard is subjected to accelerated thermal aging in a thermal aging box at 120 ℃. And then performing moisture absorption tests on the oil-immersed insulating paper boards in the non-aged state and the different thermal aging states to obtain the oil-immersed insulating paper boards with different moisture contents and aging states. This example produced oil-impregnated insulation boards having a degree of polymerization of 1286, 832, and 356, wherein the moisture content of the new oil-impregnated insulation board having a degree of polymerization of 1286 was 0.98%, 1.84%, 2.53%, 3.62%, 3.85%, and 4.51%, respectively, the moisture content of the aged oil-impregnated insulation board having a degree of polymerization of 832 was 1.24%, 1.71%, 2.08%, 3.37%, 3.77%, and 4.42%, respectively, and the moisture content of the aged oil-impregnated insulation board having a degree of polymerization of 356 was 1.13%, 1.98%, 2.76%, 3.34%, 4.12%, and 4.75%, respectively.
The frequency domain dielectric property test is carried out on the oil-immersed insulating paper board containing different moisture and aging states, and the schematic diagram of the frequency domain dielectric spectrum test system is shown in fig. 1. The IDAX-300 produced by Megger company is selected as the test instrument, the test peak voltage is 200V, and the test frequency range is 10-3-103Hz, the test temperature is 45 ℃. Obtaining frequency domain dielectric spectrums of the oil-immersed insulation paper boards with different moisture contents and aging states, taking the frequency domain dielectric spectrum of the oil-immersed insulation paper board with the polymerization degree of 832 under different moisture contents as an example, as shown in fig. 2.
2. Extracting a characteristic quantity of dielectric modulus characterizing the synergistic effect of moisture and ageing products
And converting the frequency domain dielectric curve of the oil-immersed insulating paperboard influenced by the synergistic effect of moisture and aging into a dielectric modulus spectrum curve by adopting a formula 1. Taking the dielectric modulus spectrum of the oil-impregnated insulating paperboard with the polymerization degree of 832 under different moisture contents as an example, as shown in fig. 3.
Where M' (ω) and M "(ω) represent the real and imaginary parts of the dielectric modulus, respectively. ' (ω) and "(ω) represent the real and imaginary parts of the complex permittivity in the frequency domain, respectively.
Comprehensively considering the synergistic effect of moisture and aging on the oil-immersed insulating paperboard, integrating the imaginary part of the dielectric modulus by using a formula 2 (the integral value is called a modulus factor A)(DP-mc％)) And carrying out quantitative characterization on the synergistic effect of the moisture and the aging on the oil-immersed insulating paperboard. The modulus factor A is calculated for three groups of oil-immersed insulating paper boards with different moisture and aging states(DP-mc％)The calculation results are shown in fig. 4.
Where M "(f) represents the imaginary part of the dielectric modulus and f represents the test frequency.
3. Constructing the correlation between the polymerization degree and the imaginary part integral value of the dielectric modulus of the oil-immersed insulating paperboard under the synergistic effect of the water and the aging product
And constructing a functional relation between the modulus factor and the moisture of the oil-immersed insulating paperboard under different aging states, as shown in fig. 5.
This example proposes a "degree of polymerization-moisture" translation idea, and selects a modulus factor curve with a degree of polymerization of 356 as a reference curve, and moves the modulus factor curves with a degree of polymerization of 832 and 1286 to the left of the reference curve along the horizontal direction to form a main curve, as shown in fig. 6. And fitting the main curve with a non-linear function using equation 3. In the formula, a, b and c are fitting coefficients of a nonlinear function, mc%refMoisture content under the main curve. The main curve fuses the synergistic effect of moisture and aging on the oil-immersed insulating paperboard, and is beneficial to accurately evaluating the insulating state of the oil-immersed insulating paperboard under the synergistic effect of moisture and aging.
Meanwhile, in the present embodiment, the ratio of the moisture content before curve translation to the moisture content after translation is referred to as the translation factor ψ of degree of polymerizationDPDegree of polymerization translation factor psiDPThe calculation formula is shown in formula 4. In the formula, (mc%)DPReferred to as the moisture content before curve translation, (mc%) ref is the moisture content after curve translation. The translation factors of the plots for degrees of polymerization 1286, 832 and 356 were 1, 1.281 and 1.363, respectively.
Constructing polymerization degree translation factor psi according to Allen's equation formDPAnd (1/DP)ref-1/DP) as shown in equation 5. Wherein DPrefIs the degree of polymerization corresponding to the reference curve, DP is the degree of polymerization corresponding to the translated curve, EDPIs defined as a constant related to the degree of polymerization of the oil impregnated insulating paper board. Meanwhile, taking logarithms simultaneously on both sides of the equal sign of equation 5 can obtain equation 6, and then psi can be constructedDPAnd (1/DP)ref-1/DP). In the present embodiment, ln ψDPAnd (1/DP)ref-1/DP) is fitted, the fitting graph and the fitting formula are shown in fig. 7 and formula 7, respectively. Goodness of fit of 0.99, EDPThe value size is 132.533.
According to the above analysis, the method for evaluating the aging state of the oil-impregnated insulating paper board by fusing the synergistic effect of the moisture and the aging product is obtained in this embodiment, as shown in formula 8. Finally, fusion can be derived from the formula
The degree of polymerization of the insulating board under the synergistic effect of the combined moisture and the aging product is shown in formula 9.
4. Verifying the validity of the patented method
The embodiment provides a method for evaluating the aging state of an oil-impregnated power transformer oil-paper insulation system by applying a frequency domain dielectric modulus imaginary part integral value, and the method can be used for evaluating the aging state of the oil-impregnated power transformer oil-paper insulation system by fusing the synergistic effect of moisture and an aging product. In order to verify the effectiveness of the method, an aged and damped oil-immersed insulating paperboard sample and a field oil-immersed power transformer are selected as verification objects.
(1) Laboratory-prepared insulation status assessment of oil-impregnated cellulose samples synergistically affected by aging and moisture
This example prepared oil-impregnated insulating paperboard samples with a degree of polymerization and moisture content of 356 and 1.27%, respectively, and a degree of polymerization and moisture content of 544 and 3.87%, respectively. Two oil-impregnated insulating paperboard samples obtained by an IDAX300 device are subjected to frequency domain dielectric spectrum data (a test schematic diagram is shown in figure 1), and the frequency domain dielectric spectrum data is shown in figure 8 (a). Meanwhile, the frequency domain dielectric spectrum is converted into a dielectric modulus spectrum using a formula as shown in fig. 8 (b).
Meanwhile, the imaginary part of the dielectric modulus of the oil-immersed insulating paper board in the laboratory is integrated by using the formula 2 in the embodiment so as to obtain the modulus factor A(DP-mc％). The modulus factor A of the oil-immersed insulating paperboard sample with the polymerization degree and the moisture content of 356 percent and 1.27 percent respectively and the polymerization degree and the moisture content of 544 percent and 3.87 percent respectively(DP-mc％)1.58 and 10.34 respectively. Finally, according to the modulus factor A of the two oil-immersed insulating paperboards(DP-mc％)And substituting the moisture content estimated by the testing equipment into the formula 11 in the embodiment respectively, so as to finally obtain the predicted polymerization degree of the oil-immersed insulating paperboard with the synergistic effect of the fused moisture and the aging state. In this example, the predicted polymerization degree values of the oil-impregnated insulating paperboard samples with the polymerization degree and the water content of 356 and 1.27% respectively and the polymerization degree and the water content of 544 and 3.87% respectively are 398 and 559 respectively, which are close to the actually measured polymerization degree.
(2) Evaluation of oil paper insulation aging state of field oil-immersed transformer
By combining the new evaluation method and the XY equivalent model of the transformer oil paper insulation system in the embodiment, the patent further provides a method and a flow for evaluating the aging state of the oil paper insulation of the on-site transformer, which are as follows:
in the present embodiment, an FDS test is performed on a three-winding power transformer which is actually operated, where the main insulation structure parameter of the power transformer is X ═ 0.23, Y ═ 0.48, the transformer has been put into operation for about 8 years during the test, and the service life of the transformer is in the middle and early stage, and the polymerization degree should be between 700 and 900 according to the 30-year service life expectancy calculation of the transformer. The testing equipment adopts IDAX300 of Megger company, the peak voltage is 200V, and the frequency is testedIn the range of 10-3Hz～103Hz, the temperature of the transformer is 28 ℃ during testing, and the direct current conductivity of the transformer insulating oil is 4.2 multiplied by 10 at the temperature-13And (5) S/m. In addition, the transformer was evaluated for 1.65% moisture content using the test equipment software. Complex capacitance spectrum C of tested power transformertotAs shown in fig. 9 (a). Meanwhile, the actually measured complex capacitance spectrum of the main insulation of the power transformer can be converted into a complex permittivity spectrum by equation 10, as shown in fig. 9 (b).
The main insulation structure between windings of the oil-immersed power transformer is oil-paper composite insulation, and mainly comprises a cylindrical partition plate, an oil duct and a gasket, as shown in fig. 10. The equivalent XY model is a common method for simplifying the oil-paper composite insulation between windings of an oil-immersed power transformer, as shown in fig. 10. Wherein, X is the ratio of the total thickness of the partition board to the thickness of the main insulation, and Y is the ratio of the total width of the gasket to the average circumference of the high-low voltage winding.
According to the XY model formula 11, the complex dielectric constant frequency spectrum of the oil-immersed insulating paper board in the main insulation of the transformer can be obtained by calculationPBAs shown in fig. 11 (a). σ (T) represents the direct current conductivity at temperature T,0the dielectric constant of the vacuum is constant,0＝8.85×10- 12f/m. Meanwhile, the complex dielectric constant spectrum of the oil-immersed insulating paper board in the main insulation of the transformer is converted into a dielectric modulus spectrum by using formula 1, as shown in fig. 11 (b). And performing integral calculation on the imaginary part of the dielectric modulus of the oil-immersed insulating paper board in the main insulation of the transformer by using a formula 2 to obtain a modulus factor of 1.278, and substituting the estimated moisture content into a formula 9 to obtain the predicted polymerization degree of the oil-immersed insulating paper board in the main insulation of the transformer of 776. The range of the insulation state evaluation method is consistent with the range of the main insulation DP of the transformer, and the effectiveness of the oil-immersed insulation paperboard insulation state evaluation method fusing the synergistic effect of moisture and aging is further verified.
The embodiment provides a method for evaluating the aging state of an oil-impregnated power transformer oil-paper insulation system by applying a frequency domain dielectric modulus imaginary part integral value, and the method can be used for evaluating the aging state of the oil-impregnated power transformer oil-paper insulation system by fusing the synergistic effects of moisture and an aging product. Fig. 12 shows a flowchart of the aging state evaluation of the oil-impregnated insulating paper board and the oil-impregnated transformer oil-paper insulating system.
Fig. 13 is a schematic flow chart of the implementation of the present invention.
Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.
Claims (4)
1. A method for evaluating the aging state of an oil-impregnated transformer oil paper insulation system is characterized by comprising the following steps: the method comprises the following steps:
s1: carrying out frequency domain dielectric response test on oil-immersed insulating paper boards with different moisture contents and aging states;
s2: extracting dielectric modulus characteristic quantity representing synergistic influence of the moisture and the aging product;
s3: and constructing the correlation between the polymerization degree of the oil-immersed insulating paperboard and the imaginary part integral value of the dielectric modulus under the synergistic effect of the moisture and the aging product.
2. Method for assessing the state of ageing of an oil-filled transformer oil-paper insulation system according to claim 1, characterised in that: step S1 specifically includes the following steps:
s11: carrying out accelerated thermal aging on the oil-immersed insulating paper board in a thermal aging box at 120 ℃, and then carrying out moisture absorption tests on the oil-immersed insulating paper board in an unaged state and different thermal aging states to obtain oil-immersed insulating paper boards with different moisture contents and aging states;
s12: and carrying out frequency domain dielectric characteristic test on the oil-immersed insulating paper boards containing different moisture contents and aging states to obtain frequency domain dielectric spectrums of the oil-immersed insulating paper boards containing different moisture contents and aging states.
3. Method for assessing the state of ageing of an oil-filled transformer oil-paper insulation system according to claim 2, characterized in that: step S2 specifically includes the following steps:
s21: converting the frequency domain dielectric curve of the oil-immersed insulating paperboard affected by the synergistic effect of moisture and aging into a dielectric modulus spectrum curve by adopting a formula (1):
wherein, M' (ω) and M "(ω) represent a real part and an imaginary part of the dielectric modulus, respectively; ' (ω) and "(ω) represent the real and imaginary parts of the complex permittivity in the frequency domain, respectively;
s22: comprehensively considering the synergistic effect of moisture and aging on the oil-immersed insulating paperboard, integrating the imaginary part of the dielectric modulus by adopting a formula (2), wherein the integral value is called a modulus factor A(DP-mc％)And quantifying and characterizing the synergistic effect of moisture and aging on the oil-immersed insulating paperboard:
where M "(f) represents the imaginary part of the dielectric modulus and f represents the test frequency.
4. Method for assessing the state of ageing of an oil-filled transformer oil-paper insulation system according to claim 3, characterized in that: in step S3, the method specifically includes:
s31: aiming at oil-immersed insulating paper boards in different aging states, constructing a function relation between a modulus factor and moisture;
s32: adopting a 'polymerization degree-water' translation idea, selecting a modulus factor curve with a specific polymerization degree as a reference curve, and moving the modulus factor curves with the other polymerization degrees to the reference curve along the horizontal direction to form a main curve;
s33: fitting the main curve with a non-linear function using equation (3):
wherein a, b and c are fitting coefficients of a nonlinear function, mc%refMoisture content under the main curve;
s34: the ratio of the water content before curve translation to the water content after translation is referred to as the translation factor psi of degree of polymerizationDPDegree of polymerization translation factor psiDPThe calculation formula is as follows:
in the formula, (mc%)DPIs the moisture content before curve translation, (mc%) ref is the moisture content after curve translation;
s35: constructing polymerization degree translation factor psi according to Allen's equation formDPAnd (1/DP)ref-1/DP) as follows:
wherein DPrefIs the degree of polymerization corresponding to the reference curve, DP is the degree of polymerization corresponding to the translated curve, EDPIs a constant related to the degree of polymerization of the oil-immersed insulating paperboard;
obtaining formula (6) by simultaneously taking logarithm of two sides of equal sign of formula (5), and further constructing psiDPAnd (1/DP)ref-1/DP):
s36: for ln psiDPAnd (1/DP)ref-1/DP) is fitted, the fitting formula is as follows:
s37: obtaining a formula for evaluating the aging state of the oil-immersed insulating paperboard by fusing the synergistic effect of the moisture and the aging product:
thereby deducing the polymerization degree of the insulating paperboard under the synergistic effect of the fused moisture and the aging product:
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