Temperature conversion method for dielectric loss factor of oil-immersed transformer in cold and high-altitude areas

Abstract

A temperature conversion method for the dielectric loss factor of oil-immersed transformers in high-altitude cold regions belongs to the technical field of oil-immersed transformers. The present invention solves the problem that existing methods for testing the dielectric loss factor of oil-immersed transformers cannot meet the extremely cold temperature environment in high-altitude cold regions. It includes: measuring and obtaining the actual temperature of the area where the oil-immersed transformer is located, and the dielectric loss factor at the actual temperature; rounding the actual temperature to obtain an approximate temperature, and obtaining a dielectric loss factor conversion coefficient based on a conversion table of approximate temperature and dielectric loss factor conversion coefficients; obtaining the dielectric loss factor when corrected to 20°C based on the actual temperature, the dielectric loss factor at the actual temperature, and the dielectric loss factor conversion coefficient. The present invention is used to detect the dielectric loss factor of oil-immersed transformers in high-altitude cold regions.

Description

Technical Field

[0001] The invention relates to a temperature conversion method for a dielectric loss factor of an oil-immersed transformer in a high-cold region, and belongs to the technical field of oil-immersed transformers. Background Art

[0002] Oil-immersed transformers are widely used in industrial and mining enterprises, in independent or attached agricultural substations, and in residential residential substations, and have broad application prospects. The dielectric loss factor of a transformer is a key indicator of the insulation performance of transformer oil. Therefore, accurate and efficient testing of the dielectric loss factor of oil-immersed transformers is key to evaluating the electrical performance of transformer oil.

[0003] However, the dielectric loss factor of oil-immersed transformers is significantly affected by temperature. Therefore, when measuring the dielectric loss factor of oil-immersed transformers in cold and high-temperature areas, the following problems arise:

[0004] 1. Existing technologies only offer conversion formulas for temperatures above 5°C. If testing is required in an environment below 5°C, heating (such as hot oil circulation) should be performed. However, in some high-altitude and low-temperature regions, heating equipment during field tests not only increases operational complexity but also can lead to unstable equipment operation, uneven temperature distribution of large equipment after heating, and inaccurate test data due to heating of measuring instruments.

[0005] 2. In recent years, the frequent occurrence of extreme climates has brought challenges to the stable operation of power grid equipment. Higher requirements have also been placed on the accuracy and reliability of field detection instruments in extremely cold environments. Currently, most field detection instruments are suitable for temperatures above -10°C. In an environment below -10°C, electronic components may freeze, crack, deform, or even fail, resulting in unreliable data collected by the front-end of field detection.

[0006] Therefore, it is of great significance to obtain the dielectric loss factor of the transformer in the high-altitude cold area without heating and keeping the test piece warm. Summary of the Invention

[0007] The purpose of the present invention is to solve the problem that the existing method for testing the dielectric loss factor of an oil-immersed transformer cannot meet the extremely cold temperature environment in high-altitude cold areas, and to provide a temperature conversion method for the dielectric loss factor of an oil-immersed transformer in high-altitude cold areas.

[0008] The temperature conversion method for the dielectric loss factor of an oil-immersed transformer in a high-altitude cold region of the present invention comprises:

[0009] S1. Measure and obtain the actual temperature t of the area where the oil-immersed transformer is located, as well as the dielectric loss factor at the actual temperature;

[0010] S2. rounding off the actual temperature t obtained in S1 to obtain an approximate temperature T, and obtaining a dielectric loss factor conversion coefficient K by looking up a conversion table between the approximate temperature T and the dielectric loss factor conversion coefficient K;

[0011] S3, based on the actual temperature obtained in S1, the dielectric loss factor at the actual temperature, and the dielectric loss factor conversion coefficient K obtained in S2, obtain the dielectric loss factor tanδ when corrected to 20°C 20 :

[0012] tanδ 20 =tanδ t -K(t-20);

[0013] Among them, tanδ t Indicates the dielectric loss factor at actual temperature, tanδ 20 Indicates the dielectric loss factor when corrected to 20°C.

[0014] Preferably, the conversion table of approximate temperature T and dielectric loss factor conversion coefficient K in S2 specifically includes:

[0015] The approximate temperature is -40°C, and the dielectric loss factor conversion coefficient K is -0.00307;

[0016] The approximate temperature is -35°C, and the dielectric loss factor conversion coefficient K is -0.00218;

[0017] The approximate temperature is -30°C, and the dielectric loss factor conversion coefficient K is -0.00182;

[0018] The approximate temperature is -25°C, and the dielectric loss factor conversion coefficient K is -0.00107;

[0019] The approximate temperature is -20°C, and the dielectric loss factor conversion coefficient K is -0.00015;

[0020] The approximate temperature is -15°C, and the dielectric loss factor conversion coefficient K is -0.00068;

[0021] The approximate temperature is -10°C, and the dielectric loss factor conversion coefficient K is 0.00171;

[0022] The approximate temperature is -5°C, and the dielectric loss factor conversion coefficient K is 0.0023;

[0023] The approximate temperature is -0°C, and the dielectric loss factor conversion coefficient K is 0.00253;

[0024] The approximate temperature is 5°C, and the dielectric loss factor conversion coefficient K is 0.00274;

[0025] The approximate temperature is 10°C, and the dielectric loss factor conversion coefficient K is 0.00288;

[0026] The approximate temperature is 15°C and the dielectric loss factor conversion coefficient K is 0.00282.

[0027] Preferably, the method for obtaining the conversion table of approximate temperature T and dielectric loss factor conversion coefficient K includes:

[0028] Select multiple oil-immersed transformers and determine the test temperature;

[0029] Place the testing instrument in a constant temperature box and use the reverse connection method to test the low-temperature dielectric loss factor of the high-voltage winding to the low-voltage winding and ground, the low-voltage winding to the high-voltage winding and ground, and the high-voltage winding and low-voltage winding to ground;

[0030] Draw the measured results of dielectric loss factor of multiple low-temperature oil-immersed transformers respectively;

[0031] Based on the measured results curve of dielectric loss factor of multiple oil-immersed transformers, a conversion table of approximate temperature T and dielectric loss factor conversion coefficient K is obtained.

[0032] Preferably, the specific method for determining the test temperature includes:

[0033] The ambient temperature at the test site where multiple oil-immersed transformers are located is used as the temperature reference1;

[0034] Take a small amount of transformer oil and insert it into the oil bag at the top of the transformer. Use TP300 to measure the oil temperature as the temperature reference 2.

[0035] Place the tooling for measuring the ambient temperature of the transformer oil near the test sample, avoiding direct sunlight or airflow, and use the measured oil temperature as the temperature reference 3;

[0036] If and only if the three temperature references are consistent, the current test temperature is determined.

[0037] Preferably, the dielectric loss factor includes the dielectric loss factor of oil-impregnated paperboard and the dielectric loss factor of transformer oil.

[0038] The temperature conversion method for the dielectric loss factor of oil-immersed transformers in cold regions proposed by the present invention has the following advantages:

[0039] 1. In extremely cold environments in high-altitude areas, the dielectric loss factor can be obtained without heating or keeping the test piece warm, which improves the accuracy and convenience of on-site testing. At the same time, it also improves the efficiency of on-site testing of oil-immersed transformers in extremely cold environments.

[0040] 2. The lowest detection temperature can reach -40℃, which can adapt to most high-altitude and cold areas.

[0041] 3. The maximum deviation between the calculated dielectric loss test value and the actual dielectric loss value at 20℃ shall not exceed ±5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a flow chart of the temperature conversion method for the dielectric loss factor of an oil-immersed transformer in a cold region according to the present invention;

[0043] Figure 2 This is the temperature spectrum curve of dielectric loss factor of unaged oil-impregnated paperboard;

[0044] Figure 3 This is the temperature spectrum curve of dielectric loss factor of oil-immersed paperboard with different aging degrees;

[0045] Figure 4 It is the temperature spectrum curve of the real and imaginary parts of the complex dielectric constant of the paperboard;

[0046] Figure 5 This is the temperature spectrum curve of power frequency loss factor of non-aging transformer oil;

[0047] Figure 6 This is the temperature spectrum curve of power frequency loss factor of transformer oil with different aging degrees;

[0048] Figure 7 It is a temperature spectrum curve of dielectric loss factor of transformer oil at different aging degrees;

[0049] Figure 8 This is the wiring diagram of the positive connection method for transformer dielectric loss factor test;

[0050] Figure 9 This is the wiring diagram of the reverse connection method for transformer dielectric loss factor test;

[0051] Figure 10 This is the first diagram of the measured results of the dielectric loss factor of a transformer in an extremely cold environment;

[0052] Figure 11 This is a schematic diagram of the measured results of the dielectric loss factor of the second transformer in an extremely cold environment. DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0054] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0055] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0056] Example 1:

[0057] The following combination Figure 1 This embodiment describes a temperature conversion method for the dielectric loss factor of an oil-immersed transformer in a cold region, which includes:

[0058] S1. Measure and obtain the actual temperature t of the area where the oil-immersed transformer is located, as well as the dielectric loss factor at the actual temperature;

[0059] S2. rounding off the actual temperature t obtained in S1 to obtain an approximate temperature T, and obtaining a dielectric loss factor conversion coefficient K by looking up a conversion table between the approximate temperature T and the dielectric loss factor conversion coefficient K;

[0060] S3, based on the actual temperature obtained in S1, the dielectric loss factor at the actual temperature, and the dielectric loss factor conversion coefficient K obtained in S2, obtain the dielectric loss factor tanδ when corrected to 20°C 20 :

[0061] tanδ 20 =tanδ t -K(t-20);

[0062] Among them, tanδ t Indicates the dielectric loss factor at actual temperature, tanδ 20 Indicates the dielectric loss factor when corrected to 20°C.

[0063] Furthermore, the conversion table of the approximate temperature T and the dielectric loss factor conversion coefficient K in S2 specifically includes:

[0064] The approximate temperature is -40°C, and the dielectric loss factor conversion coefficient K is -0.00307;

[0065] The approximate temperature is -35°C, and the dielectric loss factor conversion coefficient K is -0.00218;

[0066] The approximate temperature is -30°C, and the dielectric loss factor conversion coefficient K is -0.00182;

[0067] The approximate temperature is -25°C, and the dielectric loss factor conversion coefficient K is -0.00107;

[0068] The approximate temperature is -20°C, and the dielectric loss factor conversion coefficient K is -0.00015;

[0069] The approximate temperature is -15°C, and the dielectric loss factor conversion coefficient K is -0.00068;

[0070] The approximate temperature is -10°C, and the dielectric loss factor conversion coefficient K is 0.00171;

[0071] The approximate temperature is -5°C, and the dielectric loss factor conversion coefficient K is 0.0023;

[0072] The approximate temperature is -0°C, and the dielectric loss factor conversion coefficient K is 0.00253;

[0073] The approximate temperature is 5°C, and the dielectric loss factor conversion coefficient K is 0.00274;

[0074] The approximate temperature is 10°C, and the dielectric loss factor conversion coefficient K is 0.00288;

[0075] The approximate temperature is 15°C and the dielectric loss factor conversion coefficient K is 0.00282.

[0076] Furthermore, the method for obtaining the conversion table of approximate temperature T and dielectric loss factor conversion coefficient K includes:

[0077] Select multiple oil-immersed transformers and determine the test temperature;

[0078] Place the testing instrument in a constant temperature box and use the reverse connection method to test the low-temperature dielectric loss factor of the high-voltage winding to the low-voltage winding and ground, the low-voltage winding to the high-voltage winding and ground, and the high-voltage winding and low-voltage winding to ground;

[0079] Draw the measured results of dielectric loss factor of multiple low-temperature oil-immersed transformers respectively;

[0080] Based on the measured results curve of dielectric loss factor of multiple oil-immersed transformers, a conversion table of approximate temperature T and dielectric loss factor conversion coefficient K is obtained.

[0081] Furthermore, specific methods for determining the test temperature include:

[0082] The ambient temperature at the test site where multiple oil-immersed transformers are located is used as the temperature reference1;

[0083] Take a small amount of transformer oil and insert it into the oil bag at the top of the transformer. Use TP300 to measure the oil temperature as the temperature reference 2.

[0084] Place the tooling for measuring the ambient temperature of the transformer oil near the test sample, avoiding direct sunlight or airflow, and use the measured oil temperature as the temperature reference 3;

[0085] If and only if the three temperature references are consistent, the current test temperature is determined.

[0086] Furthermore, the dielectric loss factor includes the dielectric loss factor of the oil-impregnated cardboard and the dielectric loss factor of the transformer oil.

[0087] In this paper, the dielectric loss factor of oil-immersed transformers varies significantly with temperature. Currently, only conversion formulas for temperatures above 5°C are available, which are not suitable for extremely cold environments and can easily lead to misjudgment of the equipment's insulation status. Therefore, in this paper, oil-immersed cardboard and transformer oil samples were first prepared and dielectric loss factor tests were conducted in the laboratory under extremely cold conditions. The accuracy and reliability of the testing instrument under temperature were then verified in a low-temperature test chamber. Finally, a 66kV oil-immersed transformer was selected and dielectric loss factor tests were conducted under extremely cold conditions in the Greater Khingan Range region.

[0088] It was found that as the temperature decreased, the accuracy of the instrument and the display screen were significantly affected; the dielectric loss factor of the oil-immersed cardboard and transformer oil increased; the measured results of the oil-immersed transformer were consistent with the laboratory results; the dielectric loss factor increased as the temperature decreased, and the test curve was fitted and temperature converted.

[0089] The present invention can fill the gap in on-site detection methods and determination basis for the dielectric loss factor of oil-immersed transformers in extremely cold environments, solve the problem of poor reliability of detection instruments in extremely cold environments, and thus achieve accurate determination of the dielectric loss factor of oil-immersed transformers in extremely cold environments.

[0090] Detection and analysis of low-temperature dielectric loss factor of oil-paper insulation model:

[0091] Accelerated aging tests of oil-paper insulation materials and oil were carried out in the laboratory. Oil-paper insulation aging test specimens at different stages of aging, including unaged, 10 days, 20 days, 30 days, 45 days and 60 days, were prepared. Power frequency dielectric loss tests were performed on the oil-paper insulation specimens at different aging stages.

[0092] The temperature-dielectric loss factor curve measured when the oil-impregnated cardboard is not aged is as follows: Figure 2 As shown in Figure 2, the basic shapes and trends of the curves at different aging levels are approximately the same.

[0093] from Figure 2It can be seen that the dielectric loss factor of the oil-impregnated cardboard shows a trend of first decreasing and then increasing with increasing temperature. The curve starts from -40°C and shows a downward trend until 50°C, but the decline is very slow. Starting from 50°C, the loss factor of the oil-impregnated cardboard gradually increases. This is because as the temperature continues to rise, the thermal motion kinetic energy associated with the dipole increases in proportion to the temperature. After reaching a certain level, the dipole begins to rotate slowly, but when the temperature is low (less than 50°C), the turning speed of the dipole is not as fast as the changing frequency of the external electric field, so the dielectric loss factor generated is dominated by the dipole turning polarization, and the dielectric loss factor increases. After the temperature reaches 90°C, the dielectric loss factor increases sharply with temperature, and the loss factor at this time is dominated by the conductivity loss factor. Because conductivity increases exponentially with temperature, the dielectric loss factor caused by the conductivity loss factor will also surge. The temperature-loss factor corresponding curves of oil-impregnated cardboard at various aging levels are shown as follows. Figure 3 As shown in the curves, the trends of the curves are similar. With the increase of aging days, the internal structure of the oil-impregnated cardboard is seriously damaged, and the loss factor of the oil-impregnated cardboard is gradually increasing.

[0094] Figure 4 is the temperature spectrum curve of the real and imaginary parts of the complex dielectric constant of the paperboard. Figure 4 (a) It can be seen that the curves of the real part of the dielectric constant of the oil-impregnated paperboard are not very regular, but the curves under different aging conditions are roughly similar. Figure 4 (b) It can be seen that the imaginary part of the dielectric constant of the oil-immersed paperboard has a similar trend to the curve of the loss factor of the paperboard mentioned above. The influence of aging on it is also the same: the longer the aging time, the larger the imaginary part of the complex dielectric constant. This is because the imaginary part of the complex dielectric constant of the medium represents the loss factor characteristics, so the shape of the imaginary part curve and the influence law are similar to the loss factor curve.

[0095] Transformer oil dielectric loss factor test under low temperature conditions:

[0096] The temperature-dielectric loss factor curve measured for unaged transformer oil is as follows: Figure 5 The temperature-loss factor curves of transformer oil at different aging levels are shown in Figure 6 shown.

[0097] As the figure shows, the loss factor of transformer oil at various temperatures generally increases with increasing aging. For transformer oil, increasing aging increases its conductivity, increasing the oil's conduction current, and thus increasing its loss factor.

[0098] Figure 7 These are the temperature spectrum curves of the dielectric loss factor of transformer oil at different aging degrees, including the real part of the dielectric constant (a) and the imaginary part of the dielectric constant (b).

[0099] As shown in the figure, within the temperature range of -60-120°C, the real part of the transformer oil dielectric loss factor decreases with increasing temperature. Furthermore, the real part curve gradually rises and increases in value with increasing aging. The real part of the complex dielectric constant generally represents the dielectric's capacitance. As temperature rises, transformer oil's electrical storage properties decrease, which is reflected in the real part curve as a decrease with increasing temperature. The imaginary part of the dielectric constant of transformer oil is similar to that of oil-impregnated cardboard, following a similar trend to the dissipation factor curve and increasing with aging.

[0100] The test results for the dielectric loss factor of oil-impregnated cardboard and oil at low temperatures show that the dielectric loss factor of both oil-impregnated cardboard and pure oil first decreases and then increases as the temperature decreases. The trends are similar for oil-impregnated cardboard and oil at different degrees of aging: the higher the degree of aging, the greater the dielectric loss factor.

[0101] The existing dielectric loss factor calculation formula requires that the dielectric loss factor be converted to the same temperature (20°C) for longitudinal comparison using a temperature conversion formula. The transformer dielectric loss factor value (converted to 20°C) should not exceed 130% of the factory test value (20°C). According to the existing temperature conversion formula, tanδ should decrease with decreasing temperature, which is contrary to the test results. Therefore, the existing formula is no longer applicable to extremely cold environments. Therefore, combined with the results of oil-paper insulation model tests, actual transformer dielectric loss factor tests were conducted in low-temperature regions.

[0102] Dielectric loss factor test of oil-immersed transformer in extreme cold environment:

[0103] At present, there are two main methods for measuring the dielectric loss factor of a test sample at power frequency using a dielectric loss tester, namely the positive connection method and the reverse connection method. The distinction between the positive connection method and the reverse connection method is mainly based on whether the test sample is grounded. The basic schematic diagrams of the two wiring methods are as follows: Figure 8 and Figure 9 shown.

[0104] Because the grounding of oil-immersed transformers is generally not disconnected during on-site testing, dielectric loss factor measurements are usually performed using reverse wiring. For example, when testing the dielectric loss of a two-winding transformer's primary to secondary winding and ground, the primary winding is short-circuited and voltage is applied to 10kV, while the secondary winding and the housing are grounded.

[0105] Several 66kV oil-immersed transformers were selected in high-altitude cold areas to carry out dielectric loss factor tests in extremely cold environments.

[0106] To ensure accurate test data, and considering the inconsistency between ambient temperature and test sample oil temperature, the test site ambient temperature is used as temperature reference 1. A small amount of transformer oil is inserted into the oil sac at the top of the transformer and its oil temperature is measured using a TP300 as temperature reference 2. A tool for measuring the ambient temperature of the transformer oil is placed near the test sample, out of direct sunlight or airflow, and the measured oil temperature is used as temperature reference 3. The current test temperature is determined only if these three temperature references are consistent.

[0107] Several double-winding 66kV transformers were selected for actual measurement, and the testing instruments were placed in the constant temperature box mentioned above.

[0108] The reverse connection method is used to test the low-temperature dielectric loss factor of the high-voltage winding to the low-voltage winding and ground, the low-voltage winding to the high-voltage winding and ground, and the high-voltage winding and low-voltage winding to ground.

[0109] Select the test results of two transformers, as shown below: Figure 10 and Figure 11 shown.

[0110] The test results show that the dielectric loss factor of 66kV oil-immersed transformers in extreme cold environments exhibits a similar pattern to that of the oil-paper insulation model, both exhibiting a U-shaped distribution with a minimum value near -10°C to 0°C. Below this minimum temperature point, the dielectric loss factor increases as the temperature decreases, contrary to the trend outlined in current standards. This introduces a new approach to field testing of the dielectric loss factor of electrical equipment in extreme cold environments. Specifically, equipment initially deemed unqualified in extreme cold environments can be recalculated as qualified at room temperature, reducing the likelihood of normal equipment being deemed unqualified.

[0111] The test results show that although the initial values ​​of the dielectric loss factors of different 66kV transformers are different, the change patterns are similar, and the slope of the dielectric loss value at each temperature point relative to the dielectric loss value at 20℃ is close. Taking the -35℃ test data as an example, the dielectric loss value change rates of the two transformers relative to 20℃ are -0.00218 and -0.00208 respectively, and the relative deviation is only 4.8%.

[0112] Therefore, it can be used Figure 10 and Figure 11 The temperature conversion is performed on the data of different temperature points.

[0113] The conversion factors are shown in Table 1:

[0114] Table 1

[0115]

[0116]

[0117] Dielectric loss factor corrected to 20°C:

[0118] tanδ 20 =tanδ t -K(t-20)

[0119] During actual measurement, first record the test temperature, then select the conversion factor K at a similar temperature according to the above formula to convert the dielectric loss factor test value to 20°C, and then combine it with other test methods (such as water content in oil test, partial discharge test, etc.) to comprehensively judge the overall moisture condition of the equipment.

[0120] To verify the above conversion method, we visited a 66 kV transformer station in a cold region twice, in summer and winter respectively, and selected four temperature points to conduct actual measurement verification of the dielectric damage factor at low temperatures. The verification results are shown in Table 2.

[0121] The verification results show that the maximum deviation of the dielectric loss test values ​​at the four selected temperature points after conversion compared with the measured dielectric loss values ​​at 20°C does not exceed ±5%, which proves the effectiveness of the conversion method.

[0122] Table 2

[0123] Temperature T / ℃ -31 -22 0 9 20 tanδ measured results / % 0.556 0.472 0.371 0.388 0.439 Tanδ converted to 20℃ result / % 0.460 0.460 0.422 0.419 / Relative deviation / % 4.8％ 4.8％ -3.9％ -4.6％ /

[0124] Low temperatures affect the dielectric loss factor of oil-impregnated cardboard, creating an inflection point in its temperature variation. Above this inflection point, the temperature variation trend of the dielectric loss factor is consistent with the current reduction formula, increasing with increasing temperature. Below this inflection point, the dielectric loss factor trend deviates from this trend, increasing with decreasing temperature. This situation could potentially lead to transformers that haven't been exposed to moisture being identified as defective in extremely cold environments, impacting maintenance strategies.

[0125] Low temperatures affect the accuracy of dielectric loss factor test instruments and the clarity of the display screen, especially below -10°C. The data fluctuates irregularly and the display screen is unclear.

[0126] To ensure the reliability of on-site testing, it is recommended that the dielectric loss factor testing instrument be placed in a constant temperature environment above -10°C.

[0127] The effect of low temperatures on the dielectric loss factor of 66kV oil-immersed transformers is similar to that of oil-immersed cardboard. The inflection point temperature is approximately -10 to 0°C. This paper proposes a method for determining the dielectric loss factor test results of 66kV oil-immersed transformers in extremely cold environments, providing guidance for engineering applications.

[0128] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be employed in conjunction with other described embodiments.

Claims

1. Temperature conversion method for dielectric loss factor of oil-immersed transformer in cold and high-altitude areas, characterized by: It includes: S1. Measure and obtain the actual temperature t of the area where the oil-immersed transformer is located, as well as the dielectric loss factor at the actual temperature; S2. The actual temperature t obtained in S1 is rounded off to obtain an approximate temperature T, and the dielectric loss factor conversion coefficient K is obtained by querying the conversion table between the approximate temperature T and the dielectric loss factor conversion coefficient K; S3, based on the actual temperature obtained in S1, the dielectric loss factor at the actual temperature, and the dielectric loss factor conversion coefficient K obtained in S2, obtain the dielectric loss factor tanδ when corrected to 20°C 20 : tanδ 20 =tanδ t -K(t-20); Among them, tanδ t Indicates the dielectric loss factor at actual temperature, tanδ 20 Indicates the dielectric loss factor when corrected to 20°C; The method for obtaining the conversion table of approximate temperature T and dielectric loss factor conversion coefficient K includes: Select multiple oil-immersed transformers and determine the test temperature; Place the testing instrument in a constant temperature box and use the reverse connection method to test the low-temperature dielectric loss factor of the high-voltage winding to the low-voltage winding and ground, the low-voltage winding to the high-voltage winding and ground, and the high-voltage winding and low-voltage winding to ground; Draw the measured results of dielectric loss factor of multiple low-temperature oil-immersed transformers respectively; Based on the measured results of dielectric loss factors of multiple oil-immersed transformers, a conversion table of approximate temperature T and dielectric loss factor conversion coefficient K is obtained; Specific methods for determining the test temperature include: The ambient temperature at the test site where multiple oil-immersed transformers are located is used as the temperature reference1; Take a small amount of transformer oil and insert it into the oil bag at the top of the transformer. Use TP300 to measure the oil temperature as the temperature reference 2. Place the tooling for measuring the ambient temperature of the transformer oil near the test sample, avoiding direct sunlight or airflow, and use the measured oil temperature as the temperature reference 3; If and only if the three temperature references are consistent, the current test temperature is determined.

2. The temperature conversion method for dielectric loss factor of oil-immersed transformer in cold regions according to claim 1 is characterized in that: The conversion table of approximate temperature T and dielectric loss factor conversion coefficient K mentioned in S2 specifically includes: The approximate temperature is -40°C, and the dielectric loss factor conversion coefficient K is -0.00307; The approximate temperature is -35°C, and the dielectric loss factor conversion coefficient K is -0.00218; The approximate temperature is -30°C, and the dielectric loss factor conversion coefficient K is -0.00182; The approximate temperature is -25°C, and the dielectric loss factor conversion coefficient K is -0.00107; The approximate temperature is -20°C, and the dielectric loss factor conversion coefficient K is -0.00015; The approximate temperature is -15°C, and the dielectric loss factor conversion coefficient K is -0.00068; The approximate temperature is -10°C, and the dielectric loss factor conversion coefficient K is 0.00171; The approximate temperature is -5°C, and the dielectric loss factor conversion coefficient K is 0.0023; The approximate temperature is -0°C, and the dielectric loss factor conversion coefficient K is 0.00253; The approximate temperature is 5°C, and the dielectric loss factor conversion coefficient K is 0.00274; The approximate temperature is 10°C, and the dielectric loss factor conversion coefficient K is 0.00288; The approximate temperature is 15°C and the dielectric loss factor conversion coefficient K is 0.00282.

3. The temperature conversion method for dielectric loss factor of oil-immersed transformer in cold regions according to claim 1 is characterized in that: The dielectric loss factor includes the dielectric loss factor of the oil-impregnated cardboard and the dielectric loss factor of the transformer oil.

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