A Transformer Aging Status Assessment Method Based on Sludge / Trace Main Metal Content Analysis in Heavy Oil at the Bottom of the Tank

Abstract

This invention relates to a method for assessing the aging condition of transformers based on the analysis of sludge / trace main metal content in the bottom heavy oil. The method includes the following steps: collecting bottom heavy oil samples from transformers with different aging degrees; detecting the proportion of sludge in the bottom heavy oil samples to obtain the correlation between the proportion of sludge in the bottom heavy oil and the aging degree of the transformer; collecting bottom heavy oil samples from transformers whose aging degree is to be assessed; detecting the proportion of sludge in the bottom heavy oil samples; comparing the obtained detection results with the correlation between the proportion of sludge in the bottom heavy oil and the aging degree of the transformer to obtain the aging degree of the transformer to be assessed. The equipment and method involved in this invention are simple and facilitate efficient assessment of the aging condition of transformers.

Description

Technical Field

[0001] This invention relates to a method for assessing the aging condition of an oil-immersed transformer, and more particularly to a method for assessing the aging condition of a transformer based on the analysis of the content of sludge / trace main metals in the heavy oil at the bottom of the transformer tank, which belongs to the field of transformer aging condition assessment. Background Technology

[0002] Transformers are the core of energy conversion and transmission in power systems and are widely used in power grids. They transmit electrical energy from power plants to users and are also used for voltage regulation, stabilization, and isolation in distribution systems. Their normal operation is crucial for the safety and stability of the power system.

[0003] The most widely used type of transformer is the oil-immersed transformer. Its coils and cores are immersed in a large amount of insulating oil, which can effectively isolate and protect the coils and cores, giving them good insulation and cooling performance.

[0004] See Figure 1 The heavy oil at the bottom of a transformer tank is formed because the transformer oil operates under complex environments such as high temperature, high pressure, and electric field for a long time. The hydrocarbon compounds in the oil decompose due to excessive heating and oxidation, forming heavier substances. These substances settle at the bottom of the transformer as the transformer oil cools naturally or externally, forming sludge, which is the heavy oil sludge at the bottom of the transformer tank.

[0005] Studies have shown [1-2] Transformer tank bottom sludge is mainly composed of greases, resins, asphalt, carbon black, trace metal particles, metal oxides, and metal ions, primarily iron and copper ions. Greases and resins are cracking products of transformer oil under high temperature, high pressure, and electric field conditions, while asphalt is formed by the polymerization of hydrocarbons in transformer oil under long-term high temperature and high pressure. Metal ions may originate from internal transformer components such as windings, core, tank, and pipelines, all made of metal. During transformer operation, the internal insulating oil ages due to factors such as electric field strength, high temperature, humidity, and oxidation. These metal surfaces will corrode, wear, and peel off within the aged insulating oil. Simultaneously, during the early forced oil circulation of internal transformer equipment, mechanical wear will cause metal particles to gradually detach and form sludge in the insulating oil at the bottom of the transformer, resulting in the transformer tank bottom insulating oil existing in the form of heavy oil.

[0006] The presence of metallic components can cause significant damage to the internal insulation. Under high temperature and strong electromagnetic environments, the presence of metal ions can catalyze the aging of transformer oil, and the acidic substances in the aging products of transformer oil can in turn further corrode the main metal particles and metal oxides.

[0007] Chinese invention patent specification CN 106248912 B discloses a method for characterizing transformer oil aging, including the following steps: a) using an established quantitative detection method for oxygen in transformer oil, the oxygen content in transformer oils with different aging degrees is quantitatively detected to obtain the relationship between the oxygen content and the degree of aging of the transformer oil; b) the oxygen content in multiple groups of transformer oils in actual operation is quantitatively detected, and the detection results are compared with the relationship between the oxygen content and the degree of aging of the transformer oil obtained in step a) to complete the characterization of transformer oil aging. The above method can predict the degree of transformer aging to a certain extent, but it requires precise instruments such as an elemental analyzer to perform quantitative elemental analysis on the collected oil samples, which is a relatively cumbersome process and requires high-level equipment.

[0008] References:

[0009] [1] Bian Lihua, Cao Lei, Shang Zhongtao. Influence of solid particles on the insulation performance of transformer oil [J]. Electric World, 2012. DOI:CNKI:SUN:DSJI.0.2012-02-039.

[0010] [2] Ren Qiaolin, Gong Siping, Xie Zhenghan, et al. Analysis of the effect of oil sludge removal and oil treatment in extra-large transformers [J]. China Electric Power, 2006, 39(2):95-97. DOI:10.3969 / j.issn.1004-9649.2006.02.023. Summary of the Invention

[0011] In view of the shortcomings of the prior art, the purpose of this invention is to provide a simpler and more efficient method for assessing the aging condition of oil-immersed transformers.

[0012] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0013] A method for assessing the aging condition of an oil-immersed transformer includes the following steps:

[0014] S1. Collect heavy oil samples from the bottom of transformers with different aging degrees, detect the proportion α of sludge in the heavy oil sample, and obtain the correspondence between the proportion α of sludge in the heavy oil and the aging degree of the transformer.

[0015] S2. Collect heavy oil samples from the bottom of the transformer to be evaluated for its aging degree, and detect the proportion α0 of sludge in the heavy oil sample. Compare the obtained detection results with the correspondence between the proportion α of sludge in the heavy oil at the bottom of the transformer obtained in step S1 and the aging degree of the transformer to obtain the aging degree of the transformer to be evaluated.

[0016] Further, in S1, there are multiple transformers of each aging degree, and the average proportion of sludge in the heavy oil sample at the bottom of the tank is taken as the measured value of the proportion α of sludge in the heavy oil sample at the bottom of the tank of the transformer of that aging degree; preferably, the average value is the cut average value.

[0017] Furthermore, the transformers with different aging levels are transformers of the same model but with different service times; preferably, the transformers with different aging levels include those with a service time of N. min The transformer has a service life of N years. max The transformer of the year, where 0 < N min <N max .

[0018] Furthermore, assume the service life is N. min If the proportion of sludge in the heavy oil sample from the bottom of a transformer is α = λ1, then transformers with α0 < λ1 are in a state of insignificant aging. Assuming the service life is N... max If the proportion of sludge in the heavy oil sample from the bottom of the transformer tank is α = λ2, then transformers with α0 > λ2 are in a state of significant aging, and transformers with λ1 ≤ α0 ≤ λ2 are in a state of significant aging. Where 0 < N min ≤6, 10≤N max ≤25.

[0019] Furthermore, the transformers with different aging levels also include transformers with a service life of N1 years and transformers with a service life of N2 years;

[0020] It also includes the following steps:

[0021] (1) Collect heavy oil samples from the bottom of the transformer with a service life of N1 years and detect the content of trace main metals β=μ1 in the oil sludge of the heavy oil sample from the bottom of the transformer.

[0022] Heavy oil samples were collected from the bottom of a transformer with a service life of N2 years. The content of trace main metals in the sludge of the heavy oil sample was determined to be β = μ2; where N min <N1<N2<N max Preferably, N1≤15, N2≤20;

[0023] Thus, the correlation between the content β of trace main metals in the sludge of the heavy oil sample at the bottom of the transformer and the degree of transformer aging was obtained.

[0024] (2) When λ1≤α0≤λ2, detect the content β0 of trace main metals in the sludge of the heavy oil sample at the bottom of the transformer to be evaluated for aging. Compare the obtained detection results with the correspondence between the content β of trace main metals in the sludge of the heavy oil sample at the bottom of the transformer obtained in step (2) and the obvious degree of aging of the transformer to obtain the obvious degree of aging of the transformer to be evaluated.

[0025] When β0 < μ1, the aging degree of the transformer to be evaluated is Level 1 aging; when μ1 ≤ β0 ≤ μ2, the aging degree of the transformer to be evaluated is Level 2 aging; when β0 > μ2, the aging degree of the transformer to be evaluated is Level 3 aging.

[0026] The trace main metals include one or more of iron and copper.

[0027] This allows for further classification of the degree of aging of transformers that are showing obvious signs of aging, facilitating more refined management and maintenance.

[0028] Furthermore, when detecting the content of trace main metals in the sludge of the heavy oil sample at the bottom of the tank, the sludge is first mixed with an excess of inorganic acid, dissolved, and then the solid and liquid are separated to obtain a dissolution solution with a volume of V; then the concentration C of the trace main metals in the dissolution solution is measured by ion chromatography, and the content of trace main metals in the sludge of the heavy oil sample at the bottom of the tank is C·V.

[0029] Furthermore, the heavy oil samples from the bottom of each tank are collected at the same location inside the transformer tank, and the volume of each heavy oil sample is the same, ranging from 80 to 120 mL; preferably, the heavy oil samples from the bottom of each tank are collected at a location 1-2 cm away from the inner bottom surface inside the transformer tank.

[0030] Furthermore, the sludge and liquid oil in the heavy oil samples at the bottom of each tank are separated by sedimentation or centrifugation.

[0031] The present invention provides a method for assessing the aging state of an oil-immersed transformer. By analyzing the proportion of sludge in the heavy oil at the bottom of the transformer tank, the method determines whether the transformer is aging. When the proportion of sludge reaches the aging level of the transformer, the method further determines the corrosion and damage of the internal metal materials (core and windings) under long-term high temperature, strong electric field, and oil immersion conditions by analyzing the content of trace main metals in the sludge. This method provides a comprehensive assessment of the transformer's aging state, offering suggestions and a basis for the maintenance and repair of transformers in long-term operation, thereby improving the transformer's operating efficiency and reliability. The method is simple and efficient, effectively reducing the need for quantitative elemental analysis, which helps to reduce costs and improve efficiency.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) The equipment and methods involved in this invention are simple and help to achieve efficient assessment of the aging status of transformers.

[0034] (2) By assessing the aging status of the transformer and obtaining the corresponding assessment results, we can provide a reference for the formulation of the transformer maintenance and upkeep plan to ensure the normal operation of the transformer; it can also help to take targeted maintenance measures according to the health status of the transformer, thereby extending the service life of the transformer.

[0035] (3) The present invention first makes a preliminary prediction of the aging of the transformer by measuring the sludge content in the heavy oil at the bottom of the transformer tank, and then measures and evaluates the main metal content in the sludge as needed. This allows for a more detailed prediction of the aging of the transformer. The combination of preliminary and detailed prediction helps to reduce the number of measurements of trace main metals, thereby making it easier and clearer to understand the aging status and health status of the transformer, so as to better plan maintenance strategies and improve the reliability and service life of the transformer. Attached Figure Description

[0036] Figure 1 This is a diagram illustrating the mechanism and composition analysis of heavy oil and sludge formation at the bottom of an oil-immersed transformer tank.

[0037] Figure 2 This is a schematic diagram of one sampling state of the present invention.

[0038] Figure 3 This is a flowchart of the aging condition assessment of an oil-immersed transformer according to the present invention. Detailed Implementation

[0039] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0040] See Figure 3 A method for assessing the aging condition of an oil-immersed transformer includes the following steps:

[0041] S1. Collect heavy oil samples from the bottom of transformers with different aging degrees, detect the proportion α of sludge in the heavy oil sample, and obtain the correspondence between the proportion of sludge in the heavy oil and the aging degree of the transformer.

[0042] The transformers with different aging levels are transformers of the same model but with different service times; the transformers with different aging levels include those with a service time of N. min Transformers from year N1, year N2, and those with a service life of N years. max The transformer of that year, of which N min =5, N1=10, N2=20, Nmax =25;

[0043] Heavy oil samples were collected from the bottom of a transformer with a service life of N1 years, and the content of trace main metals β=μ1 in the oil sludge of the heavy oil sample was detected.

[0044] Heavy oil samples were collected from the bottom of a transformer with a service life of N2 years. The content of trace main metals in the sludge of the heavy oil sample was determined to be β = μ2; where N min <N1<N2<N max ;

[0045] Thus, the correlation between the content β of trace main metals in the sludge of the heavy oil sample at the bottom of the transformer and the degree of transformer aging was obtained.

[0046] S2. Collect heavy oil samples from the bottom of the transformer of the above-mentioned model whose aging degree is to be evaluated, and detect the proportion α0 of sludge in the heavy oil sample. Compare the obtained detection results with the correspondence between the proportion of sludge in the heavy oil at the bottom of the transformer and the aging degree of the transformer obtained in step S1 to obtain the aging degree of the transformer to be evaluated.

[0047] When λ1≤α0≤λ2, in order to further determine the degree of transformer aging, the content β0 of trace main metals in the sludge of the heavy oil sample at the bottom of the transformer to be evaluated can be further detected. The obtained detection results are compared with the aforementioned correspondence between the content β of trace main metals in the sludge of the heavy oil sample at the bottom of the transformer and the degree of transformer aging to obtain the degree of transformer aging to be evaluated.

[0048] At this point, when β0 < μ1, the aging degree of the transformer to be evaluated is Level 1 aging; when μ1 ≤ β0 ≤ μ2, the aging degree of the transformer to be evaluated is Level 2 aging; when β0 > μ2, the aging degree of the transformer to be evaluated is Level 3 aging. For details, please refer to Table 1.

[0049] The trace main metals include iron and copper.

[0050] Table 1. Correspondence between the content β0 of trace main metals in oil sludge and the degree of transformer aging.

[0051]

[0052] In S1, there are multiple transformers of each aging level. The average proportion of sludge in the heavy oil samples from the bottom of the transformers is taken as the measured value of the proportion α of sludge in the heavy oil samples from the bottom of the transformers of that aging level; the average value is a cut-off average value. Correspondingly, the cut-off average value of the content of trace main metals in the sludge in the heavy oil samples from the bottom of the transformers is taken as the measured value of the content β of trace main metals in the sludge in the heavy oil samples from the bottom of the transformers of that aging level.

[0053] Service time is N min If the proportion of sludge in the heavy oil sample from the bottom of the transformer tank is α = λ1, then transformers with α0 < λ1 are in a state of insignificant aging. In this case, the transformer's health is good, and no further assessment of the aging level is required. For transformers with a service life of N... max If the proportion of sludge in the heavy oil sample from the bottom of the transformer tank is α = λ2, then transformers with α0 > λ2 are in a state of significant aging and are in a warning state. The insulation aging is severe and needs to be dealt with in time, or even scrapped. Transformers with λ1 ≤ α0 ≤ λ2 are in a state of significant aging. At this time, it is necessary to test and compare the content of trace main metals in the sludge to further determine the degree of aging of the transformer.

[0054] When detecting the content of trace major metals in the sludge of heavy oil samples from the bottom of the tank, the sludge is first mixed with excess nitric acid, dissolved, and then the solid and liquid are separated to obtain a dissolution solution with a volume of V. The concentration C of the trace major metals in the dissolution solution is then measured using an ion chromatograph. The content m of the trace major metals in the sludge of the heavy oil samples from the bottom of the tank is then determined. 金 For C·V.

[0055] The heavy oil samples from the bottom of each transformer tank were collected at the same location inside the transformer tank, and each sample had the same volume of 100 mL. The samples were collected 1 cm from the inner bottom surface of the transformer tank. Specifically, refer to... Figure 2 A dedicated oil pump 2 was used to extract heavy oil from the bottom of transformer tank 1. The oil pump must be dry, clean, and free of any impurities. During sampling, the oil pump was fixed at the top of the transformer near the shell wall. One end of the oil pipe 3 was connected to the inlet of the oil pump, and the other end of the oil pipe was placed at the target sampling position. Using the oil pump, the settled heavy oil was extracted from the right side of the transformer shell wall (the right side when facing the transformer) at a position 1 cm from the bottom of the tank, without affecting the main circuit inside the transformer. It was stipulated that the sampling position should be the same each time and the sample size should be 100 mL to avoid different sampling positions or too much oil being collected, so as not to affect the test results. For fluorine sampling, the oil sample was placed in a dry, clean, and well-sealed container and sealed as soon as possible to avoid contamination by air, moisture, and other impurities.

[0056] The sludge and liquid oil in the heavy oil samples from the bottom of each transformer tank are separated by sedimentation, centrifugation, or filtration. Specifically: 1) When separating sludge by sedimentation, the heavy oil containing sludge from the bottom of the transformer tank is first subjected to static sedimentation treatment, usually using a sedimentation tank or sedimentation vessel. In the sedimentation tank, the sludge will settle to the bottom due to its greater weight. 2) When separating sludge by centrifugation, the centrifuge uses the centrifugal force of the liquid to separate the sludge from the liquid oil through rotation. The sludge is obtained on the outside of the centrifuge, while the cleaner liquid oil is located on the inside, thus achieving separation. 3) When separating by sampling and filtration, filtration can be performed using a filter screen or filter. By selecting a suitable filter medium and filter pore size, the sludge can be trapped on the filter screen, while the liquid oil flows out through the filter. This embodiment specifically chooses centrifugation to separate the sludge and liquid oil.

[0057] The separated sludge is placed in a container of known mass and weighed to obtain the mass m of the sludge. 泥 The location of the sludge in the 100 mL heavy oil sample (mass m) was then marked on the wall of the container. 样 The proportion α in )

[0058] α=m 泥 / m 样 .

[0059] Correspondingly, the content of trace main metals in the sludge of the heavy oil sample at the bottom of the tank is β=m 金 / m 泥 .

[0060] Finally, based on the determined aging condition of the transformer, corresponding assessments and analyses can be conducted, and appropriate maintenance and upkeep recommendations can be proposed to ensure the normal operation of the transformer.

[0061] For example, referring to Table 2, when a transformer is identified as being in a Level 1 aging state, the internal insulation of the transformer may show signs of aging and needs to be listed as a key focus, requiring corresponding maintenance and inspection at regular intervals. When a transformer is identified as being in a Level 2 aging state, the insulation material of the transformer may have begun to age, but it has not yet affected the performance of the transformer. Maintenance recommendations at this time include: a) conducting regular insulation tests to monitor the insulation condition; b) cleaning and inspection to ensure that the inside and outside of the transformer are clean and free of impurities or dirt. When a transformer is identified as being in a Level 3 aging state, the insulation material has begun to age and may have a certain impact on the performance of the transformer. Maintenance recommendations at this time include: a) strengthening insulation testing, monitoring the insulation condition, and ensuring that it can withstand the rated voltage and load; b) regularly checking the temperature and vibration of the transformer to ensure normal operation; c) checking the quality and quantity of the transformer oil and replacing the oil in a timely manner.

[0062] Table 2 Maintenance Recommendations Based on Aging Conditions

[0063]

[0064] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A method of evaluating an aging state of an oil-immersed transformer, characterized by, The method comprises the following steps: S1, collect heavy oil samples of the tank bottom of transformers with different aging degrees, detect the proportion of sludge in the heavy oil samples of the tank bottom , obtain the proportion of sludge in the heavy oil of the tank bottom and the aging degree of the transformer S2, collect a tank bottom heavy oil sample of the transformer whose aging degree is to be evaluated, and detect the proportion of sludge in the tank bottom heavy oil sample compare the obtained detection result with the proportion of sludge in the tank bottom heavy oil obtained in step S1 compare the obtained detection result with the proportion of sludge in the tank bottom heavy oil obtained in step S1 compare the obtained detection result with the proportion of sludge in the tank bottom heavy oil obtained in step S1 compare the obtained detection result with the proportion of sludge in the tank bottom heavy oil obtained in step S1 compare the obtained detection result with the proportion of sludge in the tank bottom heavy oil obtained in step S1 compare the obtained detection result with the proportion of sludge in the tank bottom heavy oil obtained in step S1 The transformer with different aging degrees includes a transformer with service time N min years and a transformer with service time N max years, wherein 0 min N max ; assuming that the proportion of sludge in the heavy oil sample of the bottom of the transformer with service time N min years is , then the transformer with 0 is in the state of no obvious aging; assuming that the proportion of sludge in the heavy oil sample of the bottom of the transformer with service time N max years is , then the transformer with 0 is in the state of very obvious aging, is in the state of obvious aging, wherein 0 min ≤6, 10 max ≤25.​​​​​​ The transformers with different aging degrees further comprise a transformer with a service time of N1 years and a transformer with a service time of N2 years. The method further comprises the following steps: (1) Collecting the heavy oil sample of the tank bottom of the transformer with service time of N1 years, detecting the content β of trace main metal in the sludge in the heavy oil sample of the tank bottom ; Collecting the heavy oil sample of the tank bottom of the transformer with service time N2, detecting the content β of trace main metal in the sludge of the heavy oil sample ; wherein, N min <N1<N2<N max ; N1≤15, N2≤20; Thus, the relationship between the content β of the trace main metal in the sludge in the tank bottom heavy oil sample and the aging degree of the transformer is obtained. (2) when ≤ ≤ , the content β0 of trace main metal in the sludge in the heavy oil sample of the tank bottom of the transformer whose aging degree to be evaluated is detected, the obtained detection result is compared with the corresponding relationship between the content β of trace main metal in the sludge in the heavy oil sample of the tank bottom obtained in step (1) and the obvious degree of aging of the transformer, and the obvious degree of aging of the transformer to be evaluated is obtained. When β0 < At that time, the aging degree of the transformer to be evaluated was clearly level one; when ≤β0≤ When β0 > 0, the aging degree of the transformer to be evaluated is clearly level two aging; At that time, the aging degree of the transformer to be evaluated was clearly level three. The trace main metal comprises one or more of iron and copper.

2. The evaluation method according to claim 1, characterized in that In S1, the number of transformers of each aging degree is multiple, and the average of the proportion of sludge in the heavy oil sample at the bottom of the tank of the transformers of the aging degree is taken as the proportion of sludge in the heavy oil sample at the bottom of the tank of the transformers of the aging degree ; the average is a trimmed average.

3. The evaluation method according to claim 1, characterized in that The transformers with different aging degrees are transformers with the same type but different service times.

4. The evaluation method according to claim 1, characterized in that When detecting the content of the trace main metal in the sludge in the tank bottom heavy oil sample, the sludge is mixed with excessive inorganic acid, and after dissolution, solid-liquid separation is performed to obtain a dissolved liquid with a volume of V; then, the ion chromatograph is used to measure the concentration C of the trace main metal in the dissolved liquid, and the content of the trace main metal in the sludge in the tank bottom heavy oil sample is C·V.

5. The method of assessment according to any one of claims 1 to 4, characterized in that, The collection positions of the tank bottom heavy oil samples are located at the same position in the transformer tank, and the volumes of the tank bottom heavy oil samples are the same and are 80-120 mL.

6. The evaluation method according to claim 5, characterized in that The collection positions of the tank bottom heavy oil samples are located at positions 1-2 cm away from the inner bottom surface of the transformer tank.

7. The assessment method according to any one of claims 1 to 6, characterized in that, The sludge in each tank bottom heavy oil sample is separated from the liquid oil by means of sedimentation separation or centrifugal separation.

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