Method for diagnosing deterioration state of oil-immersed transformer

Abstract

Provided is a method for diagnosing a deterioration state of an oil-immersed transformer that is provided with insulating oil and insulating paper, the method comprising: a step for preparing a reference insulating oil, which is the same as the insulating oil, and reference insulating paper, which the same as the insulating paper, and acquiring at least two data groups that each comprise detection amounts of at least two compounds that are contained in the reference insulating oil and the degree of polymerization of the reference insulating paper; a step for multiplying or dividing a detection amount of a compound by a constant, and thereby adjusting the detection amount of the compound to a deterioration index for selection, which is smaller than the detection amount of the compound; a step for selecting, as a deterioration index, at least one type of numerical value selected from the group consisting of the sum, the mean, the median, the first quartile, the third quartile, and the interquartile range of the deterioration index for selection that is based on a data group; a step for creating a calibration curve related to the deterioration index and the degree of polymerization on the basis of the at least two data groups; and a step for diagnosing the deterioration state of the oil-immersed transformer using the calibration curve.

Description

Method for diagnosing the deterioration status of oil-filled transformers

[0001] This disclosure relates to a method for diagnosing the deterioration state of an oil-filled transformer.

[0002] An oil-filled transformer has a configuration in which an iron core and windings coated with insulating paper are immersed in insulating oil. The lifespan of a transformer is said to be partly due to the deterioration of the insulating paper, which is generally considered impossible to replace. The deterioration of the insulating paper occurs when surge currents generated by an external short circuit during transformer operation flow through the windings, and the resulting electromagnetic and mechanical force exerts a tensile force on the insulating paper covering the windings. As a result of the tensile force applied to the insulating paper, the mechanical strength of the insulating paper decreases, and the windings coated with the insulating paper crack or break.

[0003] The mechanical strength of insulating paper correlates with its average degree of polymerization, but it is difficult to collect insulating paper from a transformer in operation in order to measure its average degree of polymerization. Therefore, by measuring the average degree of polymerization of insulating paper by another method, it is possible to determine the mechanical strength of the insulating paper and, furthermore, the lifespan of the transformer. Non-patent document 1 discloses that insulating paper generates various compounds when it deteriorates, and that the average degree of polymerization of the insulating paper can be measured from the amount of these compounds detected. The average degree of polymerization of insulating paper represents a measure of the length of cellulose molecules. As the deterioration of insulating paper progresses, the average degree of polymerization of the insulating paper decreases, and the mechanical strength also decreases accordingly. Non-patent document 1 states that an average degree of polymerization of insulating paper of 400 to 600 is a guideline for the lifespan of a transformer.

[0004] Conventionally, the relationship between the detected amount of degradation indicator compounds and the average degree of polymerization was determined in advance, and the average degree of polymerization of the insulating paper was determined from the detected amount of degradation indicator compounds in the insulating oil sampled from the transformer to be diagnosed. Non-patent documents 1 and 2 list, for example, furfural, carbon dioxide + carbon monoxide (CO2) as degradation indicator compounds. ２ The disclosed compounds include CO, water, acetone, and methanol. These compounds are thought to be produced by the decomposition of cellulose molecules in insulating paper.

[0005] Patent Document 1 discloses a method for diagnosing the deterioration state of a transformer by using lignin-derived decomposition products as deterioration indicator compounds, since lignin, although a small component in insulating paper, contributes to the mechanical strength of the insulating paper. Lignin-derived decomposition products are compounds having a benzene ring structure, such as phenol, toluene, styrene, vanillin, and coniphenylaldehyde. Patent Document 1 states that the deterioration state of the transformer can be diagnosed from the total amount of the above compounds detected.

[0006] Depending on the type of insulating paper, some compounds may not be suitable for diagnosing the deterioration state of a transformer because they produce only small amounts of the aforementioned deterioration indicator compounds. Patent Document 2 discloses a method for diagnosing the deterioration of an insulating paper used in a transformer equipped with heat-resistant insulating paper that produces very little furfural, by using nitrogen-based compounds as deterioration indicator compounds. Non-Patent Document 2 discloses a method for diagnosing the deterioration of a transformer equipped with heat-resistant insulating paper using methanol.

[0007] Patent Document 3 discloses that, for a transformer equipped with heat-resistant insulating paper, it is possible to diagnose the deterioration of the transformer from the total amount of two or more compounds from among the five furan compounds: furfural, 5-methylfurfural, 5-hydroxymethylfurfural, 2-acetylfuran, and 2-furfuryl alcohol, and that it is particularly preferable to diagnose the deterioration of the transformer from the total amount of all five compounds.

[0008] Non-patent document 3 points out that methanol is not useful as a degradation indicator compound used for diagnosing the degradation of transformers due to its high volatility.

[0009] Japanese Patent Publication No. 2014-062858, Japanese Patent Publication No. 2020-085817, Japanese Patent Publication No. 2024-043734

[0010] "Maintenance and Management of Oil-Immersed Transformers, Part IV: Deterioration Diagnosis of Oil-Immersed Transformers," Electrical Cooperative Research, Japan Electrical Cooperative Research Association, February 25, 1999, Vol. 54, No. 5 (Part 1), p. 158-169 Oscar H. Arroyo et.al., "Relationships between Methanol Marker and Mechanical Performance of Electrical Insulation Papers for Power Transformers under Accelerated Thermal Aging", IEEE Transactions on Dielectrics and Electrical Insulation Vol. 22, No. 6; December 2015, pp3625-3632Estrela Mariana Prux von Steinkirch Souza et.al., “Evaluation of the Chemical Stability of Methanol Generated during Paper Degradation in Power Transformers”, IEEE Transactions on Dielectrics and Electrical Insulation Vol. 23, No. 5; October 2016, pp3209-3214

[0011] In transformer degradation diagnosis, the evaluation of the same compound as a degradation indicator compound can vary. For example, in the degradation diagnosis of a transformer equipped with heat-resistant insulating paper, Non-Patent Document 2 discloses that methanol can be used as a degradation indicator compound, while Non-Patent Document 3 states that methanol is not suitable as a degradation indicator compound because its high volatility makes reproducibility difficult to obtain.

[0012] It is a well-known problem that the average degree of polymerization of insulating paper, determined from a single degradation indicator compound, fluctuates depending on the amount of the degradation indicator compound detected, thus degrading the accuracy of transformer degradation diagnosis.

[0013] There are several possible reasons for fluctuations in the detected levels of degradation indicator compounds. These include highly volatile compounds such as methanol, acetone, and CO2. ２ The amount of CO detected may fluctuate because it disappears due to volatilization. Furthermore, furfural compounds, widely used in diagnosing the deterioration of insulating paper, are produced in extremely small quantities from heat-resistant insulating paper, causing their detection levels to fluctuate. Additionally, the detection levels can fluctuate depending on the operating conditions of the transformer, such as the amount of oxygen and moisture in the transformer.

[0014] Furthermore, in order to improve the above-mentioned problems, Patent Document 3 discloses the use of total values ​​and average values ​​for the detected amounts of multiple degradation indicator compounds. However, in many cases, the accuracy of transformer degradation diagnosis did not improve. This was thought to be because even if total values ​​and average values ​​for multiple degradation indicator compounds were calculated, these total values ​​and average values ​​were influenced by the degradation indicator compound with the highest detected amount.

[0015] In Patent Document 3, Figure 4 shows the relationship between the total amount of 5-methylfurfural (5MEF) and 5-hydroxymethylfurfural (5HMF) and the average degree of polymerization remaining, and Figure 5 shows the relationship between the total amount of 5MEF and 2-acetylfuran (2ACF) and the average degree of polymerization remaining. In the above case, even if 5HMF in Figure 4 and 2ACF in Figure 5 are swapped, the graphs in Figures 4 and 5 will show the same results. This indicates that the detected amounts of 5HMF and 2ACF are small and therefore do not affect the total amount of the detected compounds. Furthermore, in Patent Document 3, the change in the average degree of polymerization with respect to the total amount of the five furans is small, so the average degree of polymerization cannot be accurately determined.

[0016] Furthermore, as a degradation indicator compound, CO ２ The sum of +CO is well-known, but CO ２ Furthermore, CO is highly volatile and easily dissipates, so the detected amount tends to fluctuate. ２ The amount produced is several tens of times greater than the amount produced by CO. ２ The total value of +CO is mostly CO ２ CO occupies the majority. Therefore, CO is used as a degradation indicator compound. ２ There are issues with using the sum of +CO values.

[0017] This disclosure is made in view of the above circumstances and aims to provide a method for accurately diagnosing the deterioration state of an oil-filled transformer.

[0018] The present disclosure is a method for diagnosing the deterioration state of an oil-filled transformer equipped with insulating oil and insulating paper, comprising the steps of: preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; adjusting the detected amounts of the compounds to a selectable deterioration index smaller than the detected amounts of the compounds by multiplying or dividing the detected amounts of the compounds by a constant; selecting one or more numerical values ​​as a deterioration index selected from a group consisting of the sum, mean, median, first quartile, third quartile, and interquartile range of the selectable deterioration index based on the data from the groups; creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data from the groups; and diagnosing the deterioration state of the oil-filled transformer using the calibration curve.

[0019] Another form of this implementation is a method for diagnosing the deterioration state of an oil-filled transformer equipped with insulating oil and insulating paper, comprising the steps of: preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more sets of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; adjusting the detected amounts of the compounds to a selectable deterioration index by one or more adjustments selected from the group consisting of normalization and standardization; selecting one or more numerical values ​​selected from the group consisting of the average value and median value of the selectable deterioration index based on the data from the set as a deterioration index; creating a calibration curve relating to the deterioration index and the average degree of polymerization based on two or more sets of data from the set; and diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

[0020] A method in yet another form of the present disclosure is a method for diagnosing the deterioration state of an oil-filled transformer comprising insulating oil and insulating paper, comprising the steps of: preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; adjusting the detected amounts of the compounds to a selectable deterioration index by logarithmically transforming them; selecting one or more numerical values ​​as a deterioration index from a group consisting of the sum and average values ​​of the selectable deterioration index based on the data from the groups; creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data from the groups; and diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

[0021] A method in yet another form of the present disclosure is a method for diagnosing the deterioration state of an oil-filled transformer comprising insulating oil and insulating paper, comprising the steps of: preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; selecting the synergistic mean of the detected amounts of the two or more compounds in the data group as a deterioration index; creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data; and diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

[0022] A further embodiment of the present disclosure is a method for diagnosing the deterioration state of an oil-filled transformer comprising insulating oil and insulating paper, comprising the steps of: preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and determining a compound contained in the reference insulating oil for which the coefficient of determination is 0.7 or more with respect to the detected amount of the compound and the average degree of polymerization of the reference insulating paper as a deterioration indicator compound; obtaining two or more groups of data consisting of the detected amount of the deterioration indicator compound and the average degree of polymerization of the reference insulating paper; selecting one or more numerical values ​​selected from the group consisting of the sum, mean, median, first quartile, third quartile, and interquartile range of the detected amount of the deterioration indicator compound based on the data from the groups, creating a calibration curve for the deterioration indicator and the average degree of polymerization based on the two or more groups of data from the groups, and diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

[0023] This disclosure provides a method for accurately diagnosing the deterioration state of an oil-filled transformer.

[0024] FIG. 1 is a flowchart showing an example of a method for diagnosing the deterioration state of the oil-filled transformer of the present disclosure. FIG. 2 is a conceptual diagram of a heating test apparatus used for creating a calibration curve for diagnosing the deterioration state of the transformer in the present disclosure. FIG. 3 is a diagram showing a calibration curve regarding the average value of the detected amount and the average degree of polymerization for Test Examples 1 to 9 shown in Table 6. FIG. 4 is a diagram showing a calibration curve regarding the average value of the detected amount and the average degree of polymerization for Test Examples 10 to 24 shown in Table 7. FIG. 5 is a diagram showing a calibration curve regarding the deterioration index and the average degree of polymerization in Example 1 shown in Table 10. FIG. 6 is a diagram showing a calibration curve regarding the deterioration index and the average degree of polymerization in Example 2 shown in Table 13. FIG. 7 is a diagram showing a calibration curve regarding the deterioration index and the average degree of polymerization in Example 3 shown in Table 16. FIG. 8 is a diagram showing a calibration curve regarding the deterioration index and the average degree of polymerization in Example 4 shown in Table 19. FIG. 9 is a diagram showing a calibration curve regarding the deterioration index and the average degree of polymerization in Example 5 shown in Table 23. FIG. 10 is a diagram showing a calibration curve regarding the deterioration index and the average degree of polymerization in Example 6 shown in Table 26. FIG. 11 is a diagram showing a calibration curve regarding the deterioration index and the average degree of polymerization in Example 7 shown in Table 27. FIG. 12 is a diagram showing a calibration curve regarding the detected amount of acetone and methylpyrazine and the average degree of polymerization in Tables 1 and 2. FIG. 13 is a diagram showing the relationship between the deterioration index and the average degree of polymerization in Example 8 shown in Table 29. FIG. 14 is a diagram showing a calibration curve regarding the average value of the detected amount of the compound and the average degree of polymerization in Reference Example 1 shown in Table 30. FIG. 15 is a diagram showing a calibration curve regarding the deterioration index and the average degree of polymerization in Example 9 shown in Table 31. FIG. 16 is a diagram plotting the nonpolar parameter and the boiling point for each compound. FIG. 17 is a diagram plotting the polar parameter and the boiling point for each compound. FIG. 18 is a diagram showing a graph with Ro of the compound shown in Table 28 on the X-axis and Rc on the Y-axis. FIG. 19 is a diagram showing a graph with (Ro ２ + Rc ２ ) １／２ on the X-axis and the coefficient of determination on the Y-axis. FIG. 20 is a diagram showing the relationship between the average value of the CV value and the coefficient of determination.

[0025] The embodiments of this disclosure will be described below with reference to the drawings. Note that in the drawings of this disclosure, dimensions such as length, width, thickness, and depth have been modified as appropriate for clarity and simplification, and do not represent actual dimensions.

[0026] In this disclosure, the diagnosis of the deterioration state of the oil-filled transformer to be diagnosed is achieved by estimating the average degree of polymerization of the insulating paper contained in the oil-filled transformer from the detected amounts of two or more compounds contained in the insulating oil contained in the oil-filled transformer. By estimating the average degree of polymerization of the insulating paper, the remaining lifespan of the oil-filled transformer can be estimated, making it possible to plan for the replacement of the oil-filled transformer at an appropriate time.

[0027] Embodiment 1. The method in this embodiment is a method for diagnosing the deterioration state of an oil-filled transformer equipped with insulating oil and insulating paper, and includes the steps of: preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; adjusting the detected amounts of the compounds to a selectable deterioration index smaller than the detected amounts of the compounds by multiplying or dividing the detected amounts of the compounds by a constant; selecting one or more numerical values ​​as a deterioration index selected from a group consisting of the sum, mean, median, first quartile, third quartile, and interquartile range of the selectable deterioration index based on the data from the group; creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data from the group; and diagnosing the deterioration state of the oil-filled transformer using the calibration curve.

[0028] The oil-filled transformer to be diagnosed is equipped with insulating oil and insulating paper. In the oil-filled transformer, it is preferable that the insulating paper is immersed in the insulating oil. In this specification, the oil-filled transformer to be diagnosed is also simply referred to as a transformer.

[0029] The type of insulating oil used in transformers is not particularly limited and includes, for example, mineral oil, electrically insulating oils such as alkylbenzene, and vegetable oils. Mineral oil used as an insulating oil is nonpolar.

[0030] Insulating paper contains cellulose as a constituent component, and cellulose is a highly polar molecule. Examples of insulating paper include kraft paper and heat-resistant insulating paper. Depending on the purpose, insulating paper may also contain air, copper, and pressboard. If the insulating paper is heat-resistant insulating paper, it contains a heat-resistant treatment agent. Examples of heat-resistant treatment agents include nitrogen-containing compounds such as dicyandiamide.

[0031] The method in this embodiment 1 will be described with reference to Figure 1. Figure 1 is a flowchart showing an example of a method for diagnosing the deterioration state of an oil-filled transformer according to this disclosure. The method in this embodiment 1 includes the following acquisition step S1, adjustment step S2, selection step S3, creation step S4, and diagnosis step S5. The details of each step in this embodiment 1 will be described below.

[0032] (Acquisition Process) In this process, a reference insulating oil, which is the same insulating oil as the insulating oil, and a reference insulating paper, which is the same insulating paper as the insulating paper, are prepared, and two or more sets of data consisting of the detection amount of two or more compounds contained in the reference insulating oil (hereinafter also referred to as "degradation indicator compounds") and the average degree of polymerization of the reference insulating paper are acquired.

[0033] The reference insulating oil is the same insulating oil used in the transformer being diagnosed. The reference insulating oil contains two or more degradation indicator compounds. The degradation indicator compounds contained in the reference insulating oil refer to compounds that have decomposed due to heating of the insulating paper, and may be liquid or gaseous at room temperature. Examples of degradation indicator compounds that are liquid at room temperature include compounds derived from cellulose, compounds derived from sulfur, compounds derived from heat treatment agents, and compounds derived from lignin. Examples of cellulose-derived compounds include methanol, acetone, acetic acid, furfural, furfuryl alcohol, methylfuran, and dimethylcyclohexanol. Examples of sulfur-derived compounds include dimethyl sulfone and dimethyl sulfide. Examples of heat treatment agent-derived compounds include methylpyrazine, acetamide, pyrrole, 3-methylpyrrole, 1,3-diazine, and 1-methylpyrrole. Examples of lignin-derived compounds include phenol and methylphenol. Examples of degradation indicator compounds in gases at room temperature include carbon dioxide, carbon monoxide, methane, ethane, and propane. The reference insulating oil may contain two or more of the above degradation indicator compounds, and may contain three or more.

[0034] Degradation indicator compounds contained in reference insulating oil can be detected by various methods, and can be detected in the presence of air and moisture depending on the purpose of detection. Examples of detection methods include pretreatment of the recovered reference insulating oil followed by quantification. Examples of pretreatment of the reference insulating oil include solvent extraction, headspace extraction, solid-phase extraction, solid-phase micro-extraction, and the method described in Japanese Patent Publication No. 9-72892. Methods for quantifying the degradation indicator compounds include quantification using a gas chromatograph-mass spectrometer (GC / MS).

[0035] The average degree of polymerization of the reference insulating paper represents the length of cellulose molecules, which are the main components. The deterioration of the insulating paper is caused by the decomposition of cellulose, which is a component of the insulating paper, under the influence of heating, oxygen, moisture, etc. during the operation of the transformer. Therefore, due to the deterioration of the insulating paper, the average degree of polymerization of the insulating paper decreases, which ultimately leads to the deterioration of the transformer. The average degree of polymerization of the reference insulating paper can be measured in accordance with the Japan Electrical Manufacturers' Association Standard JEM1455: Method for Measuring the Average Degree of Polymerization of Insulating Paper for Transformers (1991).

[0036] When the insulating paper included in the transformer to be diagnosed is heat-resistant insulating paper, the deterioration index compounds in the group of data obtained by the acquisition step S1 may be only compounds derived from heat treatment agents such as methylpyrazine, acetamide, pyrrole, 3-methylpyrrole, 1,3-diazine, and 1-methylpyrrole. In this case, in the acquisition step S1, the processing of subsequent steps can be facilitated by reducing the number of compounds for which the detection amount is measured. Among the above-mentioned compounds derived from heat treatment agents, a group of data may be obtained by excluding compounds with a small increasing tendency in the detection amount as the insulating paper deteriorates. For example, acetamide may be excluded.

[0037] The group of data obtained by the acquisition step S1 consists of the detection amounts of two or more deterioration index compounds and the average degree of polymerization of the reference insulating paper. The group of data can be obtained by measuring the reference insulating oil and the reference insulating paper obtained under certain conditions according to the above measurement method. The above-mentioned deterioration index compounds are two or more. From the perspective of improving the accuracy of the deterioration diagnosis of the transformer, three or more are preferred, five or more are more preferred, and seven or more are even more preferred.

[0038] In the acquisition step S1, two or more groups of data are obtained. From the perspective of improving the accuracy of the deterioration diagnosis of the transformer, it is preferably three or more groups, more preferably five or more groups, even more preferably seven or more groups, and even more preferably ten or more groups. The group of data obtained in two or more groups is obtained from different conditions. For example, it may be obtained from different heating conditions or from the normal temperature (e.g., 25°C) condition before heating.

[0039] Regarding a group of data in acquisition step S1, from the perspective of improving the accuracy of transformer degradation diagnosis, the average degree of polymerization of the reference insulating paper is preferably 800 or less, more preferably 600 or less, and even more preferably 400 or less. To make the average degree of polymerization of the reference insulating paper within the above numerical range, the reference insulating paper may be heated in the reference insulating oil, and the temperature may be 50°C or higher and 300°C or lower, may be 100°C or higher and 200°C or lower, or may be 120°C or higher and 150°C or lower. Further, the condition under which the reference insulating paper is heated in the reference insulating oil may be the temperature at which the heating of the actual transformer to be diagnosed is assumed, or may be the temperature at which an acceleration test can be performed. Also, the number of days for which the reference insulating paper is heated in the reference insulating oil may be 300 days or less, may be 200 days or less, or may be 100 days or less. The lower limit of the number of days for which the reference insulating paper is heated in the reference insulating oil is not particularly limited.

[0040] The detection of the reference insulating oil and the reference insulating paper can be performed, for example, as follows. After putting the reference insulating oil and the reference insulating paper in an arbitrary ratio in a stainless steel container, it is sealed. This is heated at an arbitrary temperature, and every time an arbitrary number of days elapses, the detection of the degradation index compound of the reference insulating oil and the measurement of the average degree of polymerization of the reference insulating paper are performed according to the method described above.

[0041] (Adjustment step) In this step, the detected amount of the degradation index compound is adjusted to a selection degradation index smaller than the detected amount of the degradation index compound by multiplying or dividing by a constant.

[0042] The selection degradation index in this embodiment is a numerical value adjusted so that the detected amount of the degradation index compound becomes smaller. The selection degradation index can be adjusted by multiplying or dividing the detected amount of the degradation index compound by a constant. According to adjustment step S2, the difference in the detected amount for each degradation index compound can be reduced. The selection degradation index is adjusted by one or more, and may be adjusted by two or more, from the detected amount for a certain degradation index compound by the constant described below.

[0043] The constant should be able to reduce the amount of degradation indicator compound detected. When multiplying the amount of degradation indicator compound detected by the constant, the constant is greater than 0 and less than 1. When dividing the amount of degradation indicator compound detected by the constant, the constant is greater than 1. The constant may be, for example, 0.1, 0.5, 10, or 100. The constant is not 1.

[0044] The constant may be a different value for each degradation indicator compound, or it may be the same value for all degradation indicator compounds. If the constant is a different value for each degradation indicator compound, for example, the constant may be 0.1 for methanol and 0.5 for acetone, and the value obtained from the amount of methanol detected in one group of data from two or more groups may be used as the constant, and the value obtained from the amount of acetone detected in one group of data from two or more groups may be used as the constant. The constant may also be the same value for all degradation indicator compounds. For example, the amount of all degradation indicator compounds detected may be divided by a constant of 0.1.

[0045] From the viewpoint of further improving the accuracy of transformer degradation diagnosis, the constant is preferably selected from one or more numerical values ​​chosen from a group consisting of the sum, mean, maximum, minimum, and median values ​​of the detected amounts of degradation indicator compounds in two or more groups of data. For example, the mean value of the detected amounts of degradation indicator compounds in two or more groups of data can be obtained as follows. Two detected amounts of a certain degradation indicator compound can be obtained from reference insulating oil heated under two different conditions, and the above mean value can be obtained by averaging these detected amounts. In this specification, "mean value" refers to the arithmetic mean unless otherwise specified.

[0046] In adjustment step S2, the amount of degradation indicator compound detected may be the measured value as is, a rounded value to facilitate the adjustment of the selectable degradation indicator, a value converted to the concentration in the reference insulating oil, or a value corrected by the detection sensitivity.

[0047] The mean value of the coefficient of variation (CV value) in a group of data consisting of two or more sets of data is preferably 1.7 or less, and more preferably 1.3 or less, from the viewpoint of further improving the accuracy of transformer deterioration diagnosis. The CV value is obtained by dividing the standard deviation of two or more selectable deterioration indicators in a group of data by the mean value of two or more selectable deterioration indicators in a group of data. One CV value can be obtained for each group of data, and two or more can be obtained depending on the number of types of adjusted selectable deterioration indicators.

[0048] (Selection Process) In this process, one or more numerical values ​​are selected as deterioration indicators from a group consisting of the sum, mean, median, first quartile, third quartile, and interquartile range of a set of data.

[0049] The degradation index is a numerical value selected using a selection degradation index based on a set of data. Therefore, the degradation index is less affected by differences in the detection amount of each degradation index compound than when it is selected using the detection amount of each degradation index compound, allowing for highly accurate determination of the average degree of polymerization of the insulating paper in the transformer being diagnosed from the calibration curve in preparation step S4. The degradation index can be selected from a group consisting of the sum of two or more selection degradation indices in a set of data, the mean, the median, the first quartile, the third quartile, and the interquartile range. Based on a single set of data, one or more numerical values ​​may be selected for the degradation index, or two or more numerical values ​​may be selected.

[0050] (Preparation Process) In this process, calibration curves for degradation indicators and average degree of polymerization are created based on data from two or more groups.

[0051] A calibration curve can be created by plotting the degradation index obtained based on data from two or more groups and the average degree of polymerization of the reference insulating paper. The degradation index is a numerical value selected from the amount of degradation index compound detected in acquisition step S1 by adjustment step S2 and selection step S3. The average degree of polymerization of the reference insulating paper is the same as the average degree of polymerization of the reference insulating paper for the group of data obtained in acquisition step S1. More than one calibration curve may be created, and from the viewpoint of improving the accuracy of transformer degradation diagnosis, it is preferable to create two or more calibration curves using two or more selected degradation indices.

[0052] From the viewpoint of improving the accuracy of transformer degradation diagnosis, the coefficient of determination of the calibration curve is preferably 0.7 or higher, more preferably 0.8 or higher, even more preferably 0.9 or higher, and even more preferably 0.95 or higher. The coefficient of determination of the calibration curve can be calculated from the numerical values ​​of the degradation index and the average degree of polymerization and the regression equation of the calibration curve. The coefficient of determination of the calibration curve is a measure that expresses the degree of agreement between the measured values ​​of the degradation index and the average degree of polymerization and the calibration curve using the least squares method. The coefficient of determination is "R ２ The coefficient of determination is expressed as being between 0 and 1. The closer the coefficient of determination is to 1, the better the match between the measured value and the calibration curve is considered to be.

[0053] (Diagnostic process) In this process, the deterioration status of the oil-filled transformer is diagnosed based on the calibration curve.

[0054] By estimating the average degree of polymerization of the insulating paper in the transformer from the created calibration curve, the deterioration state of the transformer under inspection can be diagnosed. If the average degree of polymerization of the insulating paper in the transformer is between 400 and 600, the transformer can be diagnosed as deteriorated.

[0055] The average degree of polymerization of the insulating paper in a transformer can be estimated using the following procedure, for example: The insulating oil in the transformer to be diagnosed contains two or more degradation indicator compounds. Two or more samples of insulating oil are obtained from transformers heated under different heating conditions, and the detection amounts of two or more degradation indicator compounds are obtained from these insulating oils. Next, degradation indicators are selected from the insulating oil of transformers heated under the same heating conditions as a group of data, in the same manner as the process by which degradation indicators are selected as described above. Then, by fitting the obtained degradation indicators to the regression equation obtained from the calibration curve, the average degree of polymerization of the insulating paper can be estimated.

[0056] Embodiment 2. Another embodiment of the present invention provides a method for diagnosing the deterioration state of an oil-filled transformer equipped with insulating oil and insulating paper, comprising: a step of preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; a step of adjusting the detected amounts of the compounds to a selectable deterioration index by one or more adjustments selected from the group consisting of normalization and standardization; a step of selecting one or more numerical values ​​selected from the group consisting of the average value and median value of the selectable deterioration index based on the data from the group, as a deterioration index; a step of creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data from the group; and a step of diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

[0057] The method in this second embodiment will be described with reference to Figure 1. The method in this second embodiment includes the acquisition step S1, adjustment step S2, selection step S3, creation step S4, and diagnostic step S5, similar to the method in the first embodiment. The steps in this second embodiment will be described below, but a detailed explanation of the same method as in the first embodiment will not be repeated.

[0058] (Adjustment process) In this process, the amount of degradation indicator compound detected is adjusted to a selectable degradation indicator by one or more adjustments selected from the group consisting of normalization and standardization.

[0059] In this embodiment, the selective degradation index is a numerical value obtained by adjusting the detected amount of the degradation index compound to a certain range. The selective degradation index can be adjusted by normalization or standardization as described below. According to adjustment step S2, the difference in the detected amount of each degradation index compound can be made into a numerical value within a certain range.

[0060] For normalization, it is preferable to use the difference between the minimum and maximum values ​​of the detection amount of the degradation indicator compound in one group of data from two or more groups. The detection amount of the degradation indicator compound can be normalized by the following formula (4) and the selection degradation index can be adjusted. According to formula (4), the selection degradation index is adjusted to be between α and β for any number α and β greater than 0.

[0061] [In equation (4), An represents the amount of degradation indicator compound A detected in a group of data n, An' represents the normalized value of An (selection degradation index), Amax represents the maximum amount of degradation indicator compound A detected in a group of data of two or more groups, Amin represents the minimum amount of degradation indicator compound A detected in a group of data of two or more groups, and α and β represent any number greater than 0.]

[0062] For standardization, it is preferable to use the mean and standard deviation of the detection amounts of the degradation indicator compound in one of two or more data sets. The detection amounts of the degradation indicator compound can be standardized by the following formula (5) to adjust the selection degradation index. According to formula (5), for a given degradation indicator compound, the mean value of the selection degradation index for two or more sets will be any number γ, where γ is greater than 0.

[0063] [In equation (5), Bn represents the amount of degradation indicator compound B detected in a group of data n, Bn' represents the standardized value of Bn (selection degradation index), Bave represents the average value of the amount of degradation indicator compound B detected in a group of two or more data sets, Bdev represents the standard deviation of the amount of degradation indicator compound B detected in a group of two or more data sets, and γ represents any number greater than 0.]

[0064] (Selection Process) In this process, one or more numerical values ​​are selected as degradation indicators from a group consisting of the mean and median values ​​of degradation indicators based on a set of data.

[0065] The degradation index is adjusted from a selection of degradation indices that have been normalized or standardized to a certain range by normalizing the detected amounts of all degradation index compounds. Therefore, compared to selecting a degradation index from the detected amounts of degradation index compounds, the differences in the detected amounts of each degradation index compound fall within a certain range, allowing for highly accurate determination of the average degree of polymerization of the insulating paper in the transformer being diagnosed from the calibration curve in preparation step S4. The degradation index can be selected from a group consisting of the mean and median values ​​of two or more selection of degradation indices in a group of data. The selected degradation index may be further logarithmically transformed before use.

[0066] Embodiment 3. A method in yet another embodiment of the present disclosure is a method for diagnosing the deterioration state of an oil-filled transformer comprising insulating oil and insulating paper, comprising the steps of: preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; adjusting the detected amounts of the compounds to a selectable deterioration index by logarithmically transforming them; selecting one or more numerical values ​​as a deterioration index from a group consisting of the sum and average values ​​of the selectable deterioration index based on the data from the group; creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data from the group; and diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

[0067] The method in this third embodiment will be described with reference to Figure 1. The method in this third embodiment includes an acquisition step S1, an adjustment step S2, a selection step S3, a creation step S4, and a diagnostic step S5, similar to the method in the first embodiment. The steps in this third embodiment will be described below, but a detailed explanation of the same method as in the first embodiment will not be repeated.

[0068] (Adjustment process) In this process, the amount of the degradation indicator compound detected is adjusted to a selectable degradation indicator by logarithmic transformation.

[0069] In this embodiment, the selective degradation index is a numerical value adjusted to reduce the amount of degradation index compound detected. The selective degradation index can be adjusted by logarithmic conversion of the amount of degradation index compound detected. According to adjustment step S2, the difference in the amount of each degradation index compound detected can be reduced, for example, to within one order of magnitude.

[0070] For logarithmic transformation, the base of the logarithm must be greater than 0. The logarithmic transformation may be performed using, for example, a common logarithm with base 10, or a natural logarithm with base e (Napier's number). When the detected amount of the degradation indicator compound is 0, the selection degradation index is adjusted by replacing it with the minimum detected amount of the degradation indicator compound in a different set of data for the same degradation indicator compound, and then performing a logarithmic transformation.

[0071] (Selection Process) In this process, one or more numerical values ​​are selected as deterioration indicators from a group consisting of the sum and average values ​​of the above-mentioned deterioration indicators based on a group of data.

[0072] The degradation index is a numerical value selected using a selection degradation index based on a set of data. Therefore, compared to selecting the degradation index from the detected amount of each degradation index compound, the influence of differences in the detected amount of each degradation index compound is reduced, allowing for highly accurate determination of the average degree of polymerization of the insulating paper in the transformer being diagnosed from the calibration curve in the preparation step S4. The degradation index can be selected from a group consisting of the mean and median values ​​of two or more selection degradation indices in a set of data.

[0073] Embodiment 4. A method in yet another embodiment of the present disclosure is a method for diagnosing the deterioration state of an oil-filled transformer comprising insulating oil and insulating paper, comprising the steps of: preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; selecting the synergistic mean of the detected amounts of the two or more compounds in the data from the group as a deterioration index; creating a calibration curve relating to the deterioration index and the average degree of polymerization based on two or more groups of data from the group; and diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

[0074] The method in this fourth embodiment will be described with reference to Figure 1. The method in this fourth embodiment includes an acquisition step S1, a selection step S3, a creation step S4, and a diagnostic step S5. The following describes each step in this fourth embodiment, but a detailed explanation of the same method as in the first embodiment will not be repeated.

[0075] (Selection Process) In this process, the geometric mean of the detected amounts of two or more degradation indicator compounds in a group of data is selected as the degradation indicator.

[0076] In this embodiment, the degradation index can be selected from the detection amounts of two or more degradation index compounds in a group of data using the following formula (6).

[0077] [In equation (6), Cn represents the amount of degradation indicator compound C detected in a group of data n, n is an integer greater than or equal to 1, and Cn' represents the geometric mean (degradation indicator) in a group of data n.]

[0078] Embodiment 5. A method in yet another embodiment of the present disclosure is a method for diagnosing the deterioration state of an oil-filled transformer comprising insulating oil and insulating paper, comprising the steps of: preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and determining a compound among the compounds contained in the reference insulating oil for which the coefficient of determination is 0.7 or more with respect to the detected amount of the compound and the average degree of polymerization of the reference insulating paper as a deterioration indicator compound; obtaining two or more groups of data consisting of the detected amount of the deterioration indicator compound and the average degree of polymerization of the reference insulating paper; selecting one or more numerical values ​​selected from the group consisting of the sum, mean, median, first quartile, third quartile, and interquartile range of the detected amount of the deterioration indicator compound based on the data from the groups, and creating a calibration curve for the deterioration indicator and the average degree of polymerization based on two or more groups of data from the groups; and diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

[0079] The method in this 5th embodiment will be described with reference to Figure 1. The method in this 5th embodiment includes a determination step S0, an acquisition step S1, a selection step S3, a creation step S4, and a diagnosis step S5. Each step in this 5th embodiment will be described below, but a detailed explanation of the same method as in the method in the 1st embodiment will not be repeated.

[0080] (Determination Process) In this process, a reference insulating oil, which is the same insulating oil as the insulating oil, and a reference insulating paper, which is the same insulating paper as the insulating paper, are prepared. Among the compounds contained in the reference insulating oil, compounds for which the coefficient of determination is 0.7 or higher with respect to the detected amount of the compound and the average degree of polymerization of the reference insulating paper are determined as degradation indicator compounds.

[0081] In this embodiment, the degradation indicator compound refers to a compound contained in the reference insulating oil whose coefficient of determination is 0.7 or higher with respect to the detected amount of the compound and the average degree of polymerization of the reference insulating oil. The above degradation indicator compound is a correlated compound in which the detected amount tends to increase in the transformer being diagnosed, i.e., with respect to the deterioration of the insulating paper, i.e., the decrease in the average degree of polymerization of the insulating paper. Therefore, by going through the determination step S0 before the acquisition step S1, the coefficient of determination of the calibration curve created in the creation step S4 is improved, and the accuracy of the transformer degradation diagnosis can be improved. The above coefficient of determination is 0.7 or higher, and from the viewpoint of improving the accuracy of the transformer degradation diagnosis, 0.8 or higher is preferable, and 0.9 or higher is more preferable. The coefficient of determination of the calibration curve can be calculated from the numerical values ​​of the detected amount of the compound and the average degree of polymerization of the reference insulating paper, and the regression equation of the calibration curve.

[0082] The detected amount of the compound and the average degree of polymerization of the reference insulating paper may be the measured values ​​as they are, or they may be rounded to facilitate the calculation of the coefficient of determination, or they may be corrected values ​​based on the detection sensitivity.

[0083] In the determination step S0, from the viewpoint of making the calibration curve easier to create, it is preferable to determine the degradation indicator compound from the Hansen solubility parameter and boiling point of the compound contained in the reference insulating oil. The Hansen solubility parameter is a value used to predict the solubility of a substance, and for example, values ​​reported in literature such as A, B, C, and D, as well as values ​​obtained from Hansen Solubility Parameter Software (HSPiP), can be used. HSPiP can calculate the Hansen solubility parameter from the structure of the compound. In addition, Hansen solubility parameters can also be searched on the following homepage A.Literature A: Wesley L. Archer et. Al., "Determination of Hansen Solubility Parameters for Selected Cellulose Ether Derivatives", Industrial & Engineering Chemistry Research, Vol. 30, No. 5; 1991, pp2292-2298 Literature B: Charles M. Hansen, Tim S. Poulsen, "Hansen Solubility Parameters - Biological Materials", Taylor & Francis Group, LLC; 2007, pp269-292 Document C: Martina Levin, Per Redelius “Determination of Three-Dimensional Solubility Parameters and Solubility Spheres for Naphthenic Mineral Oils”, Energy & Fuels, Vol. 22, No.5; 2008, pp3395-3401 Document D: Martina Levin, Per Redelius “Determining the Hansen Solubility Parameter of Three Corrosion Inhibitors and the "Correlation with Mineral Oil", Energy & Fuels, Vol. 26; 2012, pp7243-7250. Homepage A: HSP Basics, [online], [Retrieved November 6, 2024], Internet, <URL: https: / / www.stevenabbott.co.uk / practical-solubility / hsp-basics.php>.

[0084] The Hansen solubility parameter varies depending on the compound. The Hansen solubility parameter δ is composed of the London dispersion force δd, the dipole force δp, and the hydrogen bonding force δh, and is represented by the following formula (7). The nonpolar parameter NP in the Hansen solubility parameter δ is represented by the following formula (8). The polar parameter P in the Hansen solubility parameter δ is represented by the following formula (9). Furthermore, the compound may have a boiling point of 500°C or less, or 400°C or less, or 300°C or less.

[0085]

[0086]

[0087]

[0088] The Hansen solubility parameter and boiling point of a compound are unique values ​​for each compound. Therefore, it is sufficient to identify the physical properties of the compound from its Hansen solubility parameter and boiling point, and to estimate that the coefficient of determination for the detected amount of the compound and the average degree of polymerization of the reference insulating oil is 0.7 or higher. Using this method, even if a correlated compound is discovered that shows an increasing trend in the detected amount as the average degree of polymerization of the insulating paper decreases, it is possible to estimate that the coefficient of determination is 0.7 or higher from the Hansen solubility parameter and boiling point.

[0089] Furthermore, in the determination step S0, it is preferable to determine the degradation indicator compound by satisfying the following formulas (1) to (3) in order to facilitate the creation of a calibration curve.

[0090] [In formulas (1) to (3), δd represents the London dispersion force of the Hansen solubility parameter in the compound, δp represents the inter-dipole force of the Hansen solubility parameter in the compound, δh represents the hydrogen bonding force of the Hansen solubility parameter in the compound, δdc represents the London dispersion force of the Hansen solubility parameter in the reference insulating paper, δpc represents the inter-dipole force of the Hansen solubility parameter in the reference insulating paper, δhc represents the hydrogen bonding force of the Hansen solubility parameter in the reference insulating paper, δdo represents the London dispersion force of the Hansen solubility parameter in the reference insulating oil, δpo represents the inter-dipole force of the Hansen solubility parameter in the reference insulating oil, δho represents the hydrogen bonding force of the Hansen solubility parameter in the reference insulating oil, Rc represents the distance of the Hansen solubility parameter between the reference insulating paper and the compound, and Ro represents the distance of the Hansen solubility parameter between the reference insulating oil and the compound.]

[0091] The Hansen solubility parameters for the reference insulating paper can be those reported in the above-mentioned literature A, B, C, and D, as well as those obtained from the Hansen solubility parameter software (HSPiP). The Hansen solubility parameters for the reference insulating oil can be those reported in the above-mentioned literature A, B, C, and D, as well as those obtained from the Hansen solubility parameter software (HSPiP). The Hansen solubility parameters for the compounds can be those reported in the above-mentioned literature A, B, C, and D, as well as those obtained from the Hansen solubility parameter software (HSPiP).

[0092] (Data Acquisition Process) In this process, two or more groups of data consisting of the amount of degradation indicator compound detected and the average degree of polymerization of the reference insulating paper are acquired.

[0093] (Selection Process) In this process, one or more numerical values ​​are selected as degradation indicators from a group consisting of the sum of the detected amounts of degradation indicator compounds based on a set of data, the mean, the median, the first quartile, the third quartile, and the interquartile range.

[0094] The degradation index is a numerical value selected using the detected amount of a degradation index compound based on a set of data. Therefore, rather than selecting the degradation index from correlated and uncorrelated compounds, a calibration curve can be created from the detected amounts of correlated degradation index compounds, allowing for highly accurate determination of the average degree of polymerization of the insulating paper in the transformer being diagnosed. The degradation index can be selected from a group consisting of the sum of the detected amounts of the degradation index compound in a set of data, the mean, the median, the first quartile, the third quartile, and the interquartile range. Based on a set of data, one or more numerical values ​​may be selected as the degradation index, and two or more numerical values ​​may also be selected.

[0095] The present disclosure will be further described below with reference to examples and comparative examples, but the present disclosure is not limited to these examples.

[0096] (Heat treatment of the sample) Figure 2 is a conceptual diagram of a heating test apparatus used to create a calibration curve for diagnosing the deterioration state of a transformer in this disclosure. The heating test apparatus 1 comprises a container 10, an inlet valve 11, and a vacuum valve 12. The container 10 is a 500 ml stainless steel container that can be sealed. The inlet valve 11 is a valve for allowing degassed reference insulating oil 3 to flow into the container 10. The vacuum valve 12 is a valve for creating a vacuum in the container 10. The sample can be obtained from reference insulating paper 2 and reference insulating oil 3.

[0097] The following describes the method for obtaining the samples necessary to acquire a set of data consisting of the detection amounts of two or more degradation indicator compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper. Container 10 is sealed with 6 g of pre-dried reference insulating paper 2. Next, the inside of container 10 is evacuated using a vacuum valve 12, and after closing the vacuum valve 12, container 10 is filled with reference insulating oil 3 from the inlet valve 11. Then, with container 10 sealed by closing the inlet valve 11, it is heated at the following temperature and time to obtain samples containing the reference insulating oil and reference insulating paper under the conditions shown in Test Examples 1 to 24 below. For Test Examples 1 to 9, heat-resistant insulating paper with dicyandiamide as the heat-resistant treatment agent was used as the reference insulating paper 2. For Test Examples 10 to 24, kraft paper was used as the reference insulating paper 2. Mineral oil (JIS C 2320 Type 1 No. 4 oil) was used as the reference insulating oil 3. Test Example 1 is a sample with a heating time of 0 days.・Test Example 2 is a sample heated at 130°C for 10 days. ・Test Example 3 is a sample heated at 130°C for 30 days. ・Test Example 4 is a sample heated at 130°C for 60 days. ・Test Example 5 is a sample heated at 130°C for 120 days. ・Test Example 6 is a sample heated at 150°C for 10 days. ・Test Example 7 is a sample heated at 150°C for 30 days. ・Test Example 8 is a sample heated at 150°C for 60 days. ・Test Example 9 is a sample heated at 150°C for 120 days. ・Test Example 10 is a sample heated at 150°C for 3 days. ・Test Example 11 is a sample heated at 150°C for 7 days. ・Test Example 12 is a sample heated at 150°C for 14 days. ・Test Example 13 is a sample heated at 150°C for 30 days. - Test example 14 is a sample heated at 150°C for 60 days. - Test example 15 is a sample heated at 165°C for 1 day. - Test example 16 is a sample heated at 165°C for 3 days. - Test example 17 is a sample heated at 165°C for 5 days. - Test example 18 is a sample heated at 165°C for 7 days. - Test example 19 is a sample heated at 165°C for 14 days. - Test example 20 is a sample heated at 180°C for 0.5 days.• Test example 21 is a sample heated at 180°C for 1 day. • Test example 22 is a sample heated at 180°C for 2 days. • Test example 23 is a sample heated at 180°C for 3 days. • Test example 24 is a sample heated at 180°C for 5 days.

[0098] (Analysis of Degradation Indicator Compounds) Degradation indicator compounds that are liquid at room temperature were analyzed using a solid-phase microextraction apparatus (SPME) and a gas chromatograph / mass spectrometer (GC / MS). The specific analytical method is described below. First, 2 g of insulating oil and a stirring bar were placed in a 10 ml vial and the vial was sealed. A hole was made in the stopper large enough for the SPME syringe to pass through. The vial was placed on a stirrer and heated to 50°C at a rotation speed of 200 rpm. In this state, the SPME syringe was inserted into the space above the oil inside the vial and adsorbed for 60 minutes. The adsorbent for SPME was polydimethylsiloxane. Next, SPME was inserted into the inlet of the GC / MS and a chromatogram was obtained. The chromatograms of insulating oil heated at the above temperature and time were compared to search for compounds that changed over time, and their area values ​​(unitless) were obtained. In this disclosure, unless otherwise specified, the amount of a liquid degradation indicator compound detected at room temperature is expressed as an area value.

[0099] The detected degradation indicator compounds at room temperature were methanol, acetone, acetic acid, dimethyl sulfone, dimethyl sulfide, furfural, furfuryl alcohol, methylpyrazine, phenol, methylphenol, acetamide, pyrrole, 3-methylpyrrole, 1,3-diazine, 1-methylpyrrole, methylfuran, and dimethylcyclohexanol.

[0100] Degradation indicator compounds in the form of gases at room temperature were analyzed in accordance with the Japan Petroleum Institute standard JPI-5R-51-98, "Method for sampling and analysis of free and dissolved gases of gases and insulating oil from oil-filled electrical equipment" (1998). In this disclosure, unless otherwise specified, the detected amount of degradation indicator compounds in the form of gases at room temperature is expressed as concentration (ppm).

[0101] The degradation indicator compounds detected at room temperature that were liquid were carbon dioxide, carbon monoxide, methane, ethane, and propane.

[0102] (Analysis of average degree of polymerization) The average degree of polymerization of the insulating paper was analyzed in accordance with the Japan Electrical Manufacturers' Association standard JEM1455 "Method for measuring the average degree of polymerization of insulating paper for transformers" (1991). The average degree of polymerization of the insulating paper under the conditions shown in Test Examples 1 to 24 above was analyzed.

[0103] Test Examples 1 to 24 were analyzed according to the analysis method described above. Test Examples 1 to 24 are treated as a single group of data based on the analysis described above. Table 1 shows the amount of liquid degradation indicator compounds detected at room temperature and the average degree of polymerization of the insulating paper for Test Examples 1 to 5, and Table 2 shows the amount of liquid degradation indicator compounds detected at room temperature and the average degree of polymerization of the reference insulating paper for Test Examples 6 to 9. Table 3 shows the amount of gaseous degradation indicator compounds detected at room temperature and the average degree of polymerization of the reference insulating paper for Test Examples 10 to 14, Table 4 shows the amount of gaseous degradation indicator compounds detected at room temperature and the average degree of polymerization of the reference insulating paper for Test Examples 15 to 19, and Table 5 shows the amount of gaseous degradation indicator compounds detected at room temperature and the average degree of polymerization of the reference insulating paper for Test Examples 20 to 24.

[0104]

[0105]

[0106]

[0107]

[0108]

[0109] The above degradation indicator compounds showed an increasing trend in detection levels with increasing test time. Basic statistics, representing the detection levels of degradation indicator compounds, were calculated using spreadsheet software (Microsoft Excel). The detection levels of degradation indicator compounds in the table are the area values ​​rounded to the nearest tens, hundreds, or thousands place.

[0110] (Transformer Degradation Diagnosis) For Test Examples 1 to 24, we determined whether the calibration curves created based on the following examples and comparative examples were suitable for diagnosing the degradation state of oil-filled transformers. Specifically, we determined that if the coefficient of determination of the created calibration curve was 0.7 or higher, the degradation state could be diagnosed well.

[0111] Furthermore, it was determined that if the average value of the CV (Compound Value) for each test example used in creating the calibration curve was 1.7 or less, the deterioration state could be diagnosed more effectively. The CV value is a numerical value obtained based on the numerical values ​​used in creating the calibration curve. The numerical values ​​used in creating the calibration curve differ depending on the example and comparative example, but for example, they may be raw data of the detected amount of the deterioration indicator compound, or they may be a selection deterioration index.

[0112] <Comparative Example 1> In Comparative Example 1, for Test Examples 1 to 9 in Tables 1 and 2, the average value of the detected amount of the degradation indicator compound in a group of data was calculated, and a calibration curve was created relating this average value to the average degree of polymerization of the reference insulating paper. Table 6 shows the relationship between the average value of the detected amount and the average degree of polymerization for Test Examples 1 to 9. Figure 3 is a diagram showing the calibration curve relating the average value of the detected amount and the average degree of polymerization for Test Examples 1 to 9 shown in Table 6.

[0113]

[0114] The coefficient of determination of the calibration curve in Figure 3 was 0.3357. For Comparative Example 1, the coefficient of determination of the prepared calibration curve was not good. Furthermore, the CV values ​​obtained based on Tables 1 and 2 ranged from 1.25 to 3.4, with an average value of 2.12. Therefore, even using the calibration curve in Figure 3, the average degree of polymerization of the insulating paper could not be sufficiently estimated, resulting in poor accuracy in diagnosing the deterioration state of the transformer.

[0115] <Comparative Example 2> In Comparative Example 2, for Test Examples 10 to 24 in Tables 3 to 5, the average value of the detected amount of the degradation indicator compound in a group of data was calculated, and a calibration curve was created relating this average value to the average degree of polymerization of the reference insulating paper. Table 7 shows the relationship between the average value of the detected amount and the average degree of polymerization for Test Examples 10 to 24. Figure 4 is a diagram showing the calibration curve relating the average value of the detected amount and the average degree of polymerization for Test Examples 10 to 24 shown in Table 7.

[0116]

[0117] The coefficient of determination of the calibration curve in Figure 4 was 0.5955. For Comparative Example 2, the coefficient of determination of the created calibration curve was not good. Furthermore, the CV values ​​obtained based on Tables 3 to 5 ranged from 1.32 to 1.76, with an average value of 1.55. Therefore, even using the calibration curve in Figure 4, the average degree of polymerization of the insulating paper could not be sufficiently estimated, resulting in poor accuracy in diagnosing the deterioration state of the transformer.

[0118] For reference, the coefficient of determination of the calibration curve between the detected amount of carbon dioxide and the average degree of polymerization of the reference degree in Test Examples 10-24 in Tables 3-5 was 0.5312, which was almost the same as the coefficient of determination of the calibration curve in Figure 4. This suggests that, because carbon dioxide accounts for a large proportion of the detected amount of gaseous degradation indicator compounds at room temperature, the proportion of carbon dioxide is directly reflected even when averaging as in Comparative Example 2.

[0119] <Example 1> In Example 1, a selection degradation index and a degradation index were obtained as follows, and a calibration curve was created relating the degradation index and the average degree of polymerization of the reference insulating paper. ・Selection degradation index: The detection amounts of each degradation index compound in Tables 1 and 2 were adjusted by dividing them by the average value of the detection amounts of the degradation index compound for Test Examples 1 to 9, which was used as a constant. The constant differed for each degradation index compound. ・Degradation index: The average value of the selection degradation index in a group of data was selected. A degradation index was selected for each of Test Examples 1 to 9. Table 8 shows the selection degradation index for Example 1 for Test Examples 1 to 5. Table 9 shows the selection degradation index for Example 1 for Test Examples 6 to 9. Table 10 shows the relationship between the degradation index and the average degree of polymerization in Example 1. Figure 5 is a diagram showing the calibration curve relating the degradation index and the average degree of polymerization in Example 1, as shown in Table 10.

[0120]

[0121]

[0122]

[0123] The coefficient of determination of the calibration curve in Figure 5 was 0.9711. For Example 1, the coefficient of determination of the created calibration curve was good. The CV values ​​obtained based on Tables 8 and 9 ranged from 0.29 to 2.14, with an average value of 0.84. Therefore, the accuracy improved to the point where the average degree of polymerization of the insulating paper could be estimated using the calibration curve in Figure 5, and the deterioration state of the transformer being diagnosed could be diagnosed with high accuracy.

[0124] Furthermore, although not explained using tables and figures, calibration curves were created for the degradation index obtained by selecting the median, first quartile, third quartile, or interquartile range of the selectable degradation index shown in Tables 8 and 9, and the average degree of polymerization, and the coefficient of determination was examined. The coefficient of determination for the calibration curve obtained by selecting the median of the selectable degradation index shown in Tables 8 and 9, and the average degree of polymerization, was 0.9948. The coefficient of determination for the calibration curve obtained by selecting the first quartile of the selectable degradation index shown in Tables 8 and 9, and the average degree of polymerization, was 0.9548. The coefficient of determination for the calibration curve obtained by selecting the third quartile of the selectable degradation index shown in Tables 8 and 9, and the average degree of polymerization, was 0.9498. The coefficient of determination for the calibration curve obtained by selecting the interquartile range of the selectable degradation index shown in Tables 8 and 9, and the average degree of polymerization, was 0.7076. Therefore, regardless of which method was selected, the accuracy improved to the point where the average degree of polymerization of the insulating paper could be estimated, and the deterioration state of the transformer being diagnosed could be assessed with high accuracy.

[0125] <Example 2> In Example 2, a selection degradation index and a degradation index were obtained as follows, and a calibration curve was created relating the degradation index and the average degree of polymerization of the reference insulating paper. ・Selection degradation index: The detection amounts of each degradation index compound in Tables 1 and 2 were adjusted by dividing them by the median detection amount of the degradation index compound for Test Examples 1 to 9, using a constant. The constant differs for each degradation index compound. ・Degradation index: The median of the selection degradation index in a group of data was selected. A degradation index was selected for each of Test Examples 1 to 9. Table 11 shows the selection degradation index for Example 2 for Test Examples 1 to 5. Table 12 shows the selection degradation index for Example 2 for Test Examples 6 to 9. Table 13 shows the relationship between the degradation index and the average degree of polymerization in Example 2. Figure 6 is a diagram showing the calibration curve relating the degradation index and the average degree of polymerization in Example 2 as shown in Table 13.

[0126]

[0127]

[0128]

[0129] The coefficient of determination of the calibration curve in Figure 6 was 0.9928. For Example 2, the coefficient of determination of the created calibration curve was good. The CV values ​​obtained based on Tables 11 and 12 ranged from 0.59 to 2.56, with an average value of 1.03. Therefore, the accuracy improved to the point where the average degree of polymerization of the insulating paper could be estimated using the calibration curve in Figure 6, and the deterioration state of the transformer being diagnosed could be diagnosed with high accuracy.

[0130] Furthermore, although not explained using tables and figures, for the selection degradation index of Example 2, a calibration curve was created relating the degradation index obtained by replacing the constant with the maximum or minimum value to the average degree of polymerization, and the coefficient of determination was examined. The selection degradation index was adjusted by dividing the detected amount of each degradation index compound in Tables 1 and 2 by the maximum value of the degradation index compound for Test Examples 1 to 9, and the coefficient of determination of the calibration curve relating the selected degradation index to the average degree of polymerization was 0.9705 when the median of the selection degradation index in a group of data was used. The selection degradation index was adjusted by dividing the detected amount of each degradation index compound in Tables 1 and 2 by the minimum value of the degradation index compound for Test Examples 1 to 9, and the coefficient of determination of the calibration curve relating the selected degradation index to the average degree of polymerization was 0.9618 when the median of the selection degradation index in a group of data was used. Thus, in both cases, the accuracy was improved to the extent that the average degree of polymerization of the insulating paper could be estimated, and the degradation state of the transformer being diagnosed could be diagnosed with high accuracy.

[0131] <Example 3> In Example 3, a selective degradation index and a degradation index were obtained as follows, and a calibration curve was created relating the degradation index and the average degree of polymerization of the reference insulating paper. ・Selective degradation index: Adjusted by normalizing the detected amounts of the degradation index compounds in Tables 1 and 2. Normalization was performed according to equation (4), with α = 10 and β = 100. Therefore, the normalized selective degradation index was adjusted to be between 10 and 100. ・Degradation index: The average value of the selective degradation index in a group of data was selected. A degradation index was selected for each of the test examples 1 to 9. Table 14 shows the selective degradation index of Example 3 for test examples 1 to 5. Table 15 shows the selective degradation index of Example 3 for test examples 6 to 9. Table 16 shows the relationship between the degradation index and the average degree of polymerization in Example 3. Figure 7 is a diagram showing the calibration curve relating the degradation index and the average degree of polymerization in Example 3 shown in Table 16.

[0132]

[0133]

[0134]

[0135] The coefficient of determination of the calibration curve in Figure 7 was 0.9591. For Example 3, the coefficient of determination of the created calibration curve was good. The CV values ​​obtained based on Tables 14 and 15 ranged from 0.06 to 1.06, with an average value of 0.54. Therefore, the accuracy improved to the point where the average degree of polymerization of the insulating paper could be estimated using the calibration curve in Figure 7, and the deterioration state of the transformer being diagnosed could be diagnosed with high accuracy.

[0136] Furthermore, although not explained using tables and figures, the coefficient of determination of the calibration curve between the degradation index obtained by selecting the median of the selectable degradation indices shown in Tables 14 and 15 and the average degree of polymerization was 0.9538. Therefore, the accuracy was improved to the point where the average degree of polymerization of the insulating paper could be estimated regardless of which index was selected, and the degradation state of the transformer being diagnosed could be diagnosed with high accuracy.

[0137] <Example 4> In Example 4, a selection degradation index and a degradation index were obtained as follows, and a calibration curve was created relating the degradation index and the average degree of polymerization of the reference insulating paper. ・Selection degradation index: Adjusted by standardizing the detection amounts of each of the degradation index compounds in Tables 1 and 2. Standardization was performed according to equation (5) with γ = 1.5. ・Degradation index: The average value of the selection degradation index in a group of data was selected. A degradation index was selected for each of the test examples 1 to 9. Table 17 shows the selection degradation index for Example 4 for test examples 1 to 5. Table 18 shows the selection degradation index for Example 4 for test examples 6 to 9. Table 19 shows the relationship between the degradation index and the average degree of polymerization in Example 4. Figure 8 is a diagram showing the calibration curve relating the degradation index and the average degree of polymerization in Example 4 shown in Table 19.

[0138]

[0139]

[0140]

[0141] The coefficient of determination of the calibration curve in Figure 8 was 0.9467. For Example 4, the coefficient of determination of the prepared calibration curve was good. The CV values ​​obtained based on Tables 17 and 18 ranged from 0.21 to 0.84, with an average value of 0.40. Therefore, the accuracy improved to the point where the average degree of polymerization of the insulating paper could be estimated using the calibration curve in Figure 8, and the deterioration state of the transformer being diagnosed could be diagnosed with high accuracy.

[0142] Furthermore, although not explained using tables and figures, the coefficient of determination of the calibration curve between the degradation index obtained by selecting the median of the selectable degradation indices shown in Tables 17 and 18 and the average degree of polymerization was 0.9425. Therefore, the accuracy was improved to the point where the average degree of polymerization of the insulating paper could be estimated regardless of which index was selected, and the degradation state of the transformer being diagnosed could be diagnosed with high accuracy.

[0143] <Example 5> In Example 5, a selective degradation index and a degradation index were obtained as follows, and a calibration curve was created relating the degradation index and the average degree of polymerization of the reference insulating paper. ・Selective degradation index: Adjusted by standardizing the detection amounts of each of the degradation index compounds in Tables 3 to 5. Standardization was performed according to formula (5) with γ = 1.5. ・Degradation index: The average value of the selective degradation index in a group of data was selected. A degradation index was selected for each of the test examples 10 to 24. Table 20 shows the selective degradation index of Example 5 for test examples 10 to 14. Table 21 shows the selective degradation index of Example 5 for test examples 15 to 19. Table 22 shows the selective degradation index of Example 5 for test examples 20 to 24. Table 23 shows the relationship between the degradation index and the average degree of polymerization in Example 5. Figure 9 is a diagram showing the calibration curve relating the degradation index and the average degree of polymerization in Example 5 shown in Table 23.

[0144]

[0145]

[0146]

[0147]

[0148] The coefficient of determination of the calibration curve in Figure 9 was 0.8504. For Example 5, the coefficient of determination of the created calibration curve was good. The CV values ​​obtained based on Tables 20 to 22 ranged from 0.20 to 0.74, with an average value of 0.42. Therefore, the accuracy improved to the point where the average degree of polymerization of the insulating paper could be estimated using the calibration curve in Figure 9, and the deterioration state of the transformer being diagnosed could be diagnosed with high accuracy.

[0149] <Example 6> In Example 6, a selection degradation index and a degradation index were obtained as follows, and a calibration curve was created relating the degradation index and the average degree of polymerization of the reference insulating paper. ・Selection degradation index: Adjusted by taking the common logarithm for each of the detected amounts of degradation index compounds in Tables 1 and 2. ・Degradation index: The average value of the selection degradation index in a group of data was selected. A degradation index was selected for each of the Test Examples 1 to 9. Table 24 shows the selection degradation index of Example 6 for Test Examples 1 to 5. Table 25 shows the selection degradation index of Example 6 for Test Examples 6 to 9. Table 26 shows the relationship between the degradation index and the average degree of polymerization in Example 6. Figure 10 is a diagram showing the calibration curve relating the degradation index and the average degree of polymerization in Example 6 as shown in Table 26.

[0150]

[0151]

[0152]

[0153] The coefficient of determination of the calibration curve in Figure 10 was 0.9223. For Example 6, the coefficient of determination of the created calibration curve was good. The CV values ​​obtained based on Tables 24 and 25 ranged from 0.11 to 0.20, with an average value of 0.16. Therefore, the accuracy improved to the point where the average degree of polymerization of the insulating paper could be estimated using the calibration curve in Figure 10, and the deterioration state of the transformer being diagnosed could be diagnosed with high accuracy.

[0154] <Example 7> In Example 7, a degradation index was obtained as follows, and a calibration curve was created relating the degradation index to the average degree of polymerization of the reference insulating paper. • Degradation index: The geometric mean of the detected amounts of the degradation index compound in a group of data in Tables 1 and 2 was selected. A degradation index was selected for each of the Test Examples 1 to 9. Table 27 shows the relationship between the degradation index and the average degree of polymerization in Example 7. Figure 11 is a diagram showing the calibration curve relating the degradation index and the average degree of polymerization in Example 7, as shown in Table 27.

[0155]

[0156] The coefficient of determination of the calibration curve in Figure 11 was 0.9818. For Example 7, the coefficient of determination of the created calibration curve was good. Therefore, the accuracy improved to the point where it was possible to estimate the average degree of polymerization of the insulating paper of the transformer being diagnosed.

[0157] <Example 8> In Example 8, degradation indicator compounds and degradation indicators were obtained as follows, and a calibration curve was created relating the degradation indicator to the average degree of polymerization of the reference insulating paper. ・Degradation indicator compounds: Compounds whose coefficient of determination in the calibration curve relating the detected amount and average degree of polymerization for each compound shown in Tables 1 and 2 was 0.7 or higher were selected as degradation indicator compounds. ・Degradation indicator: The average value of the detected amount of the degradation indicator compound in a group of data was selected. A degradation indicator was selected for each of the Test Examples 1 to 9. Table 28 shows the coefficient of determination obtained from the calibration curve relating the detected amount and average degree of polymerization for each compound shown in Tables 1 and 2. In Example 8, the detected amount of the degradation indicator compound can be obtained from Tables 1 and 2. Figure 12 is a diagram showing the calibration curve relating the detected amounts and average degree of polymerization of acetone and methylpyrazine from Tables 1 and 2. In Example 8, acetone is a compound with a coefficient of determination of less than 0.7, and methylpyrazine is a degradation indicator compound with a coefficient of determination of 0.7 or higher. Table 29 shows the relationship between the degradation indicator and the average degree of polymerization in Example 8. Figure 13 shows the relationship between the degradation index and the average degree of polymerization in Example 8, as shown in Table 29.

[0158]

[0159]

[0160] The coefficient of determination of the calibration curve for the detected amount of acetone in Figure 12 was 0.0257, and the coefficient of determination of the calibration curve for the detected amount of methylpyrazine was 0.9955. From Figure 12, methylpyrazine was a better degradation indicator compound than acetone for estimating the average degree of polymerization of insulating paper. The coefficient of determination of the calibration curve in Figure 13 was 0.9908. For Example 8, the coefficient of determination of the created calibration curve was good. Based on Tables 1 and 2, the CV values ​​obtained from the detected amounts of compounds with a coefficient of determination of 0.7 or higher in Table 28 ranged from 0.15 to 1.07, with an average value of 0.61. Therefore, the accuracy was improved to the extent that the average degree of polymerization of insulating paper could be estimated using the calibration curve in Figure 13, and the degradation state of the transformer being diagnosed could be diagnosed with high accuracy.

[0161] <Reference Example 1> In Reference Example 1, a calibration curve was prepared in the same manner as in Comparative Example 1, except that the detected amounts were only those of compounds derived from the heat-resistant treatment agents methylpyrazine, acetamide, pyrrole, 3-methylpyrrole, 1,3-diazine, and 1-methylpyrrole, among the degradation indicator compounds in Comparative Example 1. Table 30 shows the relationship between the average detected amount of the compounds and the average degree of polymerization in Reference Example 1. Figure 14 is a diagram showing the calibration curve relating the average detected amount of the compounds and the average degree of polymerization in Reference Example 1 shown in Table 30.

[0162]

[0163] The coefficient of determination of the calibration curve in Figure 14 was 0.9556. Based on Tables 1 and 2, the CV values ​​obtained from the detected amounts of compounds derived from the heat-resistant treatment agent ranged from 0.85 to 1.79, with an average value of 1.29. However, values ​​deviating from the calibration curve were observed in the dotted line portion of Figure 13.

[0164] <Example 9> In Example 9, a selection degradation index and a degradation index were obtained as follows, and a calibration curve was created relating the degradation index and the average degree of polymerization of the reference insulating paper. ・Selection degradation index: Adjusted by normalizing the detection amounts of each of the compounds listed in Reference Example 1. Normalization was performed according to equation (4), with α = 10 and β = 100. Therefore, the normalized selection degradation index was adjusted to be between 10 and 100. ・Degradation index: The average value of the selection degradation index in a group of data was selected. A degradation index was selected for each of the Test Examples 1 to 9. Table 31 shows the relationship between the degradation index and the average degree of polymerization in Example 9. Figure 15 is a diagram showing the calibration curve relating the degradation index and the average degree of polymerization in Example 9 shown in Table 31.

[0165]

[0166] The coefficient of determination of the calibration curve in Figure 15 was 0.9645. For Example 9, the coefficient of determination of the created calibration curve was good. Based on Tables 14 and 15, the CV values ​​obtained from the compounds listed in Reference Example 1 ranged from 0.0 to 0.76, with an average value of 0.38, which was better than the calibration curve in Reference Example 1. Therefore, using the calibration curve in Figure 15, the accuracy improved to the point where the average degree of polymerization of the insulating paper could be estimated from the amount of compounds detected only from the heat-resistant insulating paper, and the deterioration state of the transformer being diagnosed could be diagnosed with high accuracy.

[0167] <Example 10> In Example 10, degradation indicator compounds were determined from the Hansen solubility parameters and boiling points of compounds contained in the reference insulating oil. Figure 16 is a plot of the nonpolarity parameters and boiling points for each compound. Figure 17 is a plot of the polarity parameters and boiling points for each compound. The nonpolarity parameter can be obtained from equation (8). The polarity parameter can be obtained from equation (9). In Figures 16 and 17, ○ represents a plot of compounds with a coefficient of determination of 0.7 or higher, and ● represents a plot of compounds with a coefficient of determination of less than 0.7.

[0168] From Figure 16, for compounds with a boiling point of 300°C or lower, if the boiling point is higher than 7 times the nonpolarity parameter raised to the power of -9, the coefficient of determination for that compound is 0.7 or higher. From Figure 17, for compounds with a boiling point of 300°C or lower, if the boiling point is higher than 1700 times the polarity parameter raised to the power of 6.7, the coefficient of determination for that compound is 0.7 or higher.

[0169] <Example 11> In Example 11, compounds satisfying formulas (1) to (3) were determined as degradation indicator compounds for the Hansen solubility parameters of the compounds, reference insulating paper, and reference insulating oil. Figure 18 is a graph showing the compounds listed in Table 28 with Ro on the X axis and Rc on the Y axis. The Hansen solubility parameters (δdc, δpc, δhc) of the insulating paper were (26.1, 7.9, 17.3). The Hansen solubility parameters (δdo, δpo, δho) of the insulating oil were (16.6, 0.0, 5.0). The Hansen solubility parameters of each compound were obtained from the above-mentioned documents A, B, C, D, and homepage A, as well as from the Hansen solubility parameter software (HSPiP). In Figure 18, compounds plotted between the dashed line and the dotted line are compounds with a coefficient of determination of 0.7 or higher. Figure 19 shows the (Ro) of the compounds listed in Table 28. ２ +Rc ２ ) １／２ This figure shows a graph with the x-axis representing the coefficient of determination and the y-axis representing the coefficient of determination. According to Figure 19, (Ro ２ +Rc ２ ) １／２ <If the 25 conditions are met, it was found that the compound has a coefficient of determination of 0.7 or higher.>

[0170] <Reference Example 2> Example 12 summarizes the relationship between the average value of the CV value and the coefficient of determination of the calibration curve, as described in previous examples. Figure 20 shows the relationship between the average value of the CV value and the coefficient of determination. From Figure 20, it can be seen that a good coefficient of determination cannot be obtained when the average value of the CV value exceeds 1.5.

[0171] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications are intended to be within the meaning and scope of the equivalents of the claims.

[0172] S0 Decision process, S1 Acquisition process, S2 Adjustment process, S3 Selection process, S4 Production process, S5 Diagnostic process, 1 Heating test apparatus, 10 Container, 11 Inlet valve, 12 Vacuum valve, 2 Reference insulating paper, 3 Reference insulating oil.

Claims

1. A method for diagnosing the deterioration state of an oil-filled transformer equipped with insulating oil and insulating paper, comprising: a step of preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; a step of adjusting the detected amounts of the compounds to a selectable deterioration index smaller than the detected amounts of the compounds by multiplying or dividing the detected amounts of the compounds by a constant; a step of selecting one or more numerical values ​​as a deterioration index selected from a group consisting of the sum, mean, median, first quartile, third quartile, and interquartile range of the selectable deterioration index based on the data from the group; a step of creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data from the group; and a step of diagnosing the deterioration state of the oil-filled transformer using the calibration curve.

2. The method according to claim 1, wherein the constant is selected from one or more numerical values ​​chosen from the group consisting of total value, mean value, maximum value, minimum value, and median value for the amount detected for each compound in the data of one of two or more groups.

3. A method for diagnosing the deterioration state of an oil-filled transformer equipped with insulating oil and insulating paper, comprising: a step of preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; a step of adjusting the detected amounts of the compounds to a selectable deterioration index by one or more adjustments selected from the group consisting of normalization and standardization; a step of selecting one or more numerical values ​​selected from the group consisting of the average value and median value of the selectable deterioration index based on the data from the group, as a deterioration index; a step of creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data from the group; and a step of diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

4. The method according to claim 3, wherein the normalization is performed using the difference between the minimum and maximum values ​​of the detected amounts of the compound in two or more groups of data, and the standardization is performed using the mean and standard deviation of the detected amounts of the compound in two or more groups of data.

5. A method for diagnosing the deterioration state of an oil-filled transformer equipped with insulating oil and insulating paper, comprising: a step of preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; a step of adjusting the detected amounts of the compounds to a selectable deterioration index by logarithmically transforming them; a step of selecting one or more numerical values ​​as a deterioration index from a group consisting of the sum and average values ​​of the selectable deterioration index based on the data from the group; a step of creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data from the group; and a step of diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

6. A method for diagnosing the deterioration state of an oil-filled transformer equipped with insulating oil and insulating paper, comprising: a step of preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and obtaining two or more groups of data consisting of the detected amounts of two or more compounds contained in the reference insulating oil and the average degree of polymerization of the reference insulating paper; a selection step of selecting the synergistic mean value of the detected amounts of the two or more compounds in the group of data as a deterioration index; a step of creating a calibration curve relating the deterioration index and the average degree of polymerization based on two or more groups of data; and a step of diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

7. A method for diagnosing the deterioration state of an oil-filled transformer equipped with insulating oil and insulating paper, comprising: a step of preparing a reference insulating oil which is the same insulating oil as the insulating oil and a reference insulating paper which is the same insulating paper as the insulating paper, and determining a compound among the compounds contained in the reference insulating oil whose coefficient of determination is 0.7 or more with respect to the detected amount of the compound and the average degree of polymerization of the reference insulating paper as a deterioration indicator compound; a step of obtaining two or more groups of data consisting of the detected amount of the deterioration indicator compound and the average degree of polymerization of the reference insulating paper; a step of selecting one or more numerical values ​​selected from a group consisting of the sum, mean, median, first quartile, third quartile, and interquartile range of the detected amount of the deterioration indicator compound based on the data from the groups, as a deterioration index; a step of creating a calibration curve for the deterioration index and the average degree of polymerization based on two or more groups of data from the groups; and a step of diagnosing the deterioration state of the oil-filled transformer based on the calibration curve.

8. The method according to claim 7, wherein in the step of determining the above, a degradation indicator compound is determined from the Hansen solubility parameter and boiling point of the compound.

9. The method according to claim 7, wherein the degradation indicator compound is determined in the determination step by satisfying the following formulas (1) to (3). [In formulas (1) to (3), δd represents the London dispersion force of the Hansen solubility parameter in the compound, δp represents the dipole force of the Hansen solubility parameter in the compound, δh represents the hydrogen bonding force of the Hansen solubility parameter in the compound, δdc represents the London dispersion force of the Hansen solubility parameter in the reference insulating paper, δpc represents the dipole force of the Hansen solubility parameter in the reference insulating paper, δhc represents the hydrogen bonding force of the Hansen solubility parameter in the reference insulating paper, δdo represents the London dispersion force of the Hansen solubility parameter in the reference insulating oil, δpo represents the dipole force of the Hansen solubility parameter in the reference insulating oil, δho represents the hydrogen bonding force of the Hansen solubility parameter in the reference insulating oil, and Rc represents the distance of the Hansen solubility parameter between the reference insulating paper and the compound.] Ro represents the distance of the Hansen solubility parameter between the reference insulating oil and the compound.

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