Method for measuring methanol in transformer oil paper insulation paper based on pure water extraction

Abstract

The invention discloses a method for measuring methanol in transformer oil paper insulation paper based on pure water extraction, and relates to the technical field of transformer oil paper insulation. The invention aims to solve the problem that the detection result of the existing method for detecting the methanol content in the transformer insulation paper is inaccurate. According to the method for measuring methanol in transformer oil paper insulation paper based on pure water extraction, obstruction of insulation oil on the surface of the insulation paper is relieved through ultrasonic oscillation, the release efficiency of methanol is greatly improved through the ultrasonic oscillation technology, experimental errors are reduced, and the method has remarkable advantages especially under the condition that the insulation paper is provided with an oil film. And multiple extraction is combined with accurate calculation, so that comprehensive detection of the methanol content is ensured, and the method is more reliable compared with one-time extraction. Therefore, the methanol content in the transformer insulation paper is calculated.

Description

Technical Field

[0001] The invention belongs to the technical field of transformer oil-paper insulation. Background Art

[0002] At present, oil-immersed power transformers are widely used in power grids. The main feature of oil-immersed power transformers is that they use insulating oil as a carrier and build an oil-paper insulation system with insulating paper to maintain the insulation strength inside the transformer. Studies have shown that most failures of oil-immersed power transformers are caused by poor insulation performance. Therefore, studying the insulation performance of oil-immersed power transformers is of great significance for the safe and stable operation of power systems.

[0003] At present, the research on chemical products of insulation aging has reached the third generation product methanol, which is not only highly stable, but also produced in both insulation paper and insulation oil. The methanol in the transformer oil-paper insulation system mainly comes from the degradation of cellulose in the insulation paper, and then gradually diffuses from the insulation paper to the insulation oil through molecular thermal motion until a dynamic equilibrium is reached, so that methanol forms a certain equilibrium ratio coefficient between the oil and paper. Due to the polarity effect of chemical substances, methanol has a similar polarity to the insulation paper and an opposite polarity to the insulation oil, so methanol is not easily soluble in the insulation oil. Usually, the methanol content in the insulation paper is much higher than that in the insulation oil. Limited by the lack of detection means, the current detection of methanol in transformer oil-paper insulation is mostly to detect methanol in the oil. There is a lack of effective methods for accurately detecting the methanol content in the insulation paper. The total methanol content produced by the insulation paper can only be used to infer the aging state of the insulation paper using the methanol content in the oil. However, the equilibrium ratio coefficient of methanol between oil and paper is affected by many factors such as temperature, moisture, and insulation paper type. This method of indirectly inferring the total methanol content to evaluate the degree of aging and degradation of the insulation paper is inaccurate, resulting in large evaluation errors. Furthermore, there is a lack of a relatively accurate calculation method to calculate the concentration of methanol in the transformer oil-paper insulation paper.

[0004] There is a method for measuring methanol in transformer insulation paper that uses ethanol as an extractant. Ethanol and methanol have similar peak times in gas chromatographs, so using ethanol to extract methanol from insulation paper will cause measurement errors. In addition, using organic matter as a solvent will cause the risk of contaminating the headspace sampler and gas chromatograph.

[0005] Therefore, it is particularly important to explore the detection method of methanol in insulating paper, find out the total content of methanol produced by cellulose aging and degradation in insulating paper, and accurately predict the aging degree of insulating paper. Summary of the invention

[0006] The present invention aims to solve the problem that the detection results of the existing detection method for methanol content in transformer insulation paper are inaccurate, and now provides a method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction.

[0007] The measurement method of methanol in transformer oil-paper insulation paper based on pure water extraction includes:

[0008] Step 1: In the kth extraction cycle, the insulating paper to be tested is completely immersed in pure water and the container containing the pure water is sealed;

[0009] Step 2: placing the container in a 40° C. environment for 3 days, or placing the container at room temperature for 3 to 5 days, and shaking the container with ultrasound 3 times a day, and shaking at 40° C. for 1 hour each time;

[0010] Step 3: Shake the solution in the container evenly, then take out the insulating paper to be tested in the container and place it on top of the container until no more droplets of the insulating paper to be tested fall into the container;

[0011] Step 4: Measure the methanol concentration in the solution at the upper, middle and lower layers of the solution in the container respectively, and take the average value of the three as the methanol concentration C in the kth extraction cycle k ;

[0012] Step 5: Determine whether the methanol concentration in the kth extraction cycle is lower than 50 ppb, if yes, execute step 6, otherwise set k=k+1, and then return to step 1;

[0013] Step 6: When k = 1, calculate the total methanol content x in the tested insulating paper according to the following formula:

[0014] x=C1V,

[0015] Wherein, C1 is the methanol concentration in the first extraction cycle, and V is the volume of the extraction solution;

[0016] When k≥2, calculate the total methanol content x in the tested insulating paper according to the following formula:

[0017]

[0018] Among them, C k-1 is the methanol concentration in the k-1th extraction cycle.

[0019] Furthermore, in the above step 2, the interval between two adjacent oscillation starting points is 8 hours.

[0020] Furthermore, in the above step 4, the methanol concentration in the solution is measured using a gas chromatograph.

[0021] Furthermore, the method for measuring the methanol concentration in the solution using a gas chromatograph is as follows:

[0022] Take 10 ml of the solution in the container and put it into the headspace bottle;

[0023] Heat the headspace bottle containing the solution to 80°C to evaporate the methanol in the solution;

[0024] 500 μl of gas from the upper layer of the headspace bottle was extracted and injected into the gas chromatograph to obtain the methanol front area, and the methanol concentration was obtained by the internal standard method.

[0025] Furthermore, the headspace bottle is heated in a water bath.

[0026] Furthermore, a gas-tight needle is used to extract the upper layer of gas in the headspace bottle.

[0027] Furthermore, in the above step 5, when k≥2, the calculation method of the total methanol content x in the measured insulating paper is:

[0028] Assuming the oil-paper partition coefficient is n and n<1, the methanol content calculation equation is constructed:

[0029]

[0030] Calculate the ratio of formula (k) to formula (k-1) and obtain:

[0031]

[0032] Will Substituting into formula (1), we obtain:

[0033]

[0034] Furthermore, before starting all steps, the insulating paper to be tested is pretreated, and the pretreatment method is:

[0035] Wipe off the insulating oil on the surface of the insulating paper to be tested.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction of the present invention uses pure water to extract methanol in insulation paper according to the mechanism that methanol and pure water are mutually soluble in any proportion. Ultrasonic oscillation is used to reduce the obstruction of insulating oil on the surface of insulation paper. Ultrasonic oscillation technology greatly improves the release efficiency of methanol and reduces experimental errors, especially when the insulation paper has an oil film, showing significant advantages. The methanol concentration in water is measured, and multiple extractions are performed until no methanol can be measured. Multiple extractions are combined with accurate calculations to ensure comprehensive detection of methanol content, which is more reliable than single extraction. The methanol content in transformer insulation paper is thereby calculated. Therefore, the present invention is simple to operate, and only requires an ultrasonic oscillator and a gas chromatograph to complete the experiment of extracting methanol from paper, that is, the required detection equipment is easily available. It has been experimentally verified that the accuracy and reliability are high. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Flow chart of the method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction. DETAILED DESCRIPTION

[0039] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0040] Reference Figure 1 Specifically describing this embodiment, the method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction described in this embodiment does not include:

[0041] S1. Pre-treat the transformer insulation paper.

[0042] After taking out the insulating paper from the transformer, wipe off the insulating oil on the surface of the insulating paper and weigh it. The weight is recorded as ag.

[0043] S2. Conduct extraction experiment on transformer insulation paper.

[0044] S21. In the kth extraction cycle, the insulating paper is immediately immersed in pure water and sealed. The pure water should cover the insulating paper and fill the container to prevent methanol from evaporating into the air through water vapor, resulting in methanol loss.

[0045] S22. Place the container carrying pure water in a heating box and heat it at 40°C for 3 days (or at room temperature for 3-5 days). During the static period, use ultrasonic vibration to vibrate the container 3 times a day, each time for 1 hour, and the vibration temperature is 40°C to break up the oil film on the surface of the insulation paper so that the methanol in the insulation paper can be fully diffused into the pure water.

[0046] In practical applications, the interval between two adjacent oscillation starting points can be set to 8 hours to make the oscillation more uniform.

[0047] S23. After extraction, perform simple shaking to evenly distribute the methanol in the water;

[0048] S24, open the sealed port of the container, take out the insulating paper and let it stand until no water drops. Then take a point from each of the upper, middle and lower layers of the extraction solution, measure the methanol concentration at the three points using a gas chromatograph and take the average value as the kth extraction cycle.

[0049] The method for measuring methanol concentration using gas chromatograph is:

[0050] Take 10 ml of the extraction solution and put it into the headspace bottle.

[0051] The headspace bottle containing the extraction solution was heated to 80°C in a water bath to evaporate the methanol in the extraction solution.

[0052] 500 μl of gas from the upper layer of the headspace bottle was extracted with a gas-tight needle and injected into the gas chromatograph to obtain the methanol front area, and the methanol concentration was obtained by the internal standard method.

[0053] S25, judging whether the methanol concentration in the kth extraction cycle is lower than 50 ppb, if yes, completing the extraction experiment and executing S3, otherwise setting k=k+1, and then returning to S21.

[0054] S3. Calculate the methanol content in transformer insulation paper.

[0055] When k=1, the oil-paper partition coefficient is 1. Assuming the total methanol content is x (in mg), the total methanol content x is calculated according to the following formula:

[0056] x=C1V,

[0057] Wherein, C1 is the methanol concentration in the first extraction cycle, and V is the volume of the extraction solution.

[0058] When k≥2, assuming that the oil-paper partition coefficient is n and n<1, the methanol content calculation equation is constructed:

[0059]

[0060] Among them, C k is the methanol concentration in the kth extraction cycle.

[0061] Calculate the ratio of formula (k) to formula (k-1) and obtain:

[0062]

[0063] Substituting the above formula into formula (1), we obtain:

[0064]

[0065] In summary, since ethanol and methanol have similar peak times in the gas chromatograph, using ethanol to extract methanol from insulating paper will cause measurement errors. In addition, using organic matter as a solvent will cause the risk of contaminating the headspace sampler and the gas chromatograph. According to the mechanism that methanol and pure water are miscible in any proportion, this embodiment uses pure water to extract methanol from paper to complete the measurement of the methanol content in the paper, which is convenient to operate, simple to calculate, and has high judgment accuracy.

[0066] When the content of methanol in transformer oil-paper insulation paper is effectively obtained, the degree of aging of the oil-paper insulation system can be effectively monitored, and the safe operation of the transformer can be better guaranteed and the efficiency of use can be improved. At the same time, the economic benefits of the power system industry are increased. The research on methanol in transformer oil-paper sterilization paper has not only become an effective measure for transformer monitoring and maintenance, but also is conducive to the development and progress of the power industry towards a faster scientific and technological path, and plays a significant role in building a more reliable and safe power system.

[0067] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction, characterized in that: include: Step 1: In the kth extraction cycle, the insulating paper to be tested is completely immersed in pure water and the container containing the pure water is sealed; Step 2: placing the container in a 40° C. environment for 3 days, or placing the container at room temperature for 3 to 5 days, and shaking the container with ultrasound 3 times a day, and shaking at 40° C. for 1 hour each time; Step 3: Shake the solution in the container evenly, then take out the insulating paper to be tested in the container and place it on top of the container until no more droplets of the insulating paper to be tested fall into the container; Step 4: Measure the methanol concentration in the solution at the upper, middle and lower layers of the solution in the container respectively, and take the average value of the three as the methanol concentration C in the kth extraction cycle k ; Step 5: Determine whether the methanol concentration in the kth extraction cycle is lower than 50 ppb, if yes, execute step 6, otherwise set k=k+1, and then return to step 1; Step 6: When k = 1, calculate the total methanol content x in the tested insulating paper according to the following formula: x=C1V, Wherein, C1 is the methanol concentration in the first extraction cycle, and V is the volume of the extraction solution; When k≥2, calculate the total methanol content x in the tested insulating paper according to the following formula: Among them, C k-1 is the methanol concentration in the k-1th extraction cycle.

2. The method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction according to claim 1, characterized in that: In the step 2, the interval between two adjacent oscillation starting points is 8 hours.

3. The method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction according to claim 1, characterized in that: In the step 4, the methanol concentration in the solution is measured using a gas chromatograph.

4. The method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction according to claim 3, characterized in that: The method for measuring the methanol concentration in the solution using a gas chromatograph is: Take 10 ml of the solution in the container and put it into the headspace bottle; Heat the headspace bottle containing the solution to 80°C to evaporate the methanol in the solution; 500 μl of gas from the upper layer of the headspace bottle was extracted and injected into the gas chromatograph to obtain the methanol front area, and the methanol concentration was obtained by the internal standard method.

5. The method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction according to claim 4, characterized in that: The headspace bottle was heated in a water bath.

6. The method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction according to claim 5, characterized in that: Use a gas-tight needle to extract the upper layer of gas in the headspace bottle.

7. The method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction according to claim 1, characterized in that: In step 5, when k≥2, the calculation method of the total methanol content x in the measured insulating paper is: Assuming the oil-paper partition coefficient is n and n<1, the methanol content calculation equation is constructed: Calculate the ratio of formula (k) to formula (k-1) and obtain: Will Substituting into formula (1), we obtain:

8. The method for measuring methanol in transformer oil-paper insulation paper based on pure water extraction according to any one of claims 1 to 7, characterized in that: Before starting all steps, the insulating paper to be tested is pretreated, and the pretreatment method is as follows: Wipe off the insulating oil on the surface of the insulating paper to be tested.

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