Method for diagnosing the risk of malfunction in oil-filled cables
The diagnostic method for oil-filled cables uses dissolved copper, dielectric loss tangent, and combustible gas measurements to accurately assess copper sulfide formation, addressing the inadequacies of existing methods and ensuring precise risk evaluation.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TOKYO ELECTRIC POWER CO HOLDINGS INC
- Filing Date
- 2022-01-31
- Publication Date
- 2026-06-04
Smart Images
Figure 0007869965000012 
Figure 0007869965000013 
Figure 0007869965000001
Abstract
Description
[Technical Field]
[0001] This invention relates to a method for diagnosing the risk of malfunction in oil-filled cables. [Background technology]
[0002] It is known that oil-filled electrical equipment, such as oil-filled transformers, can suffer fatal damage due to dielectric breakdown caused by the reaction of copper components in the oil with sulfur components in the insulating oil, which generates conductive copper sulfide (sulfidation corrosion). The estimated sulfur components in the insulating oil include sulfur components contained in the insulating oil itself, sulfur components leached from materials such as insulating paper, and sulfur components added to the insulating oil as antioxidants.
[0003] In oil-filled electrical equipment such as large transformers, oil-impregnated paper is used as an insulator. When copper sulfide adheres to this oil-impregnated insulating paper, a short circuit occurs between the coils, leading to its destruction. This has been reported as a case of dielectric breakdown overseas. Furthermore, while the deterioration of oil-filled cables, which also use oil-impregnated paper as an insulator, was thought to be very slow, cases of dielectric breakdown in aged oil-filled cable lines have been confirmed in recent years.
[0004] The reaction mechanism involved in copper sulfide formation in oil-filled electrical equipment such as large transformers has been studied in detail in relation to the antioxidant dibenzyl disulfide (hereinafter sometimes abbreviated as "DBDS") added to the insulating oil. Specifically, it has been reported that DBDS is adsorbed onto the coil copper, then DBDS reacts with the coil copper to form a DBDS-copper complex, and further, the DBDS-copper complex decomposes into benzyl radicals and benzyl sulfenyl radicals to form copper sulfide (see Patent Documents 1-3).
[0005] In Patent Document 1 and Patent Document 2, a method is disclosed in which insulating oil is collected from an operating transformer, and DBDS, its decomposition products, by-products, etc. are analyzed to predict the formation of copper sulfide and diagnose the risk of abnormal occurrence of oil-filled electrical equipment. Further, in Patent Document 3, a method is disclosed in which when the insulating oil is in an air atmosphere, the concentration of dibenzyl sulfoxide in the insulating oil is measured, and based on this concentration, the amount of copper sulfide formed is estimated.
[0006] However, the diagnostic methods of Patent Documents 1 to 3 above require that DBDS be added to the insulating oil. Basically, in the case of an oil-filled cable using insulating oil without DBDS added, there is a problem that the amount of copper sulfide formed in the insulating oil cannot be estimated from the amount of DBDS-copper complex formed in the insulating oil. Further, conventionally, as an inspection technique for oil-filled cables, measurement of the dielectric loss tangent (tanδ) of the insulating oil, analysis of the gas in the insulating oil, and oil-in-gas analysis using the amount of combustible gas generated by partial discharge (local insulation breakdown of the insulating oil) as a measure of the degree of deterioration are common, and a method for diagnosing the risk from the formation status of organic copper compounds and copper sulfide has not been implemented.
Prior Art Documents
Patent Documents
[0007]
Patent Document 1
Patent Document 2
Patent Document 3
Summary of the Invention
Problems to be Solved by the Invention
[0008] The present invention has been made in view of the above conventional problems, and an object thereof is to provide a diagnostic method for accurately evaluating the risk of abnormal occurrence of an oil-filled cable by estimating the formation status of organic copper compounds and copper sulfide in the oil-filled cable and comprehensively evaluating characteristic values in the formation period of the organic copper compounds and copper sulfide. [Means for solving the problem]
[0009] To solve the aforementioned problems, the inventors conducted diligent research. As a result, from the dismantling and investigation of oil-filled cables using insulating oil, they focused on the following: copper sulfide is generated even in such oil-filled cables; a correlation is observed between the amount of dissolved copper in the insulating oil (hereinafter referred to as "amount of dissolved copper in oil"), which is thought to be the cause of copper sulfide generation, and the dielectric loss tangent (tanδ) of the insulating oil; when organic copper compounds and copper sulfide are generated, the values of the amount of dissolved copper in oil, the dielectric loss tangent (tanδ), and the total amount of combustible gas (TCG) tend to decrease after reaching a maximum value in the trend graph showing the change over time; when organic copper compounds and copper sulfide are generated, a combustible gas containing hydrogen is generated in the insulating oil, and the total amount of combustible gas (TCG) in the insulating oil increases; and when organic copper compounds and copper sulfide are generated, several characteristic values change. Furthermore, we discovered that the formation status of organic copper compounds and copper sulfide can be estimated from the amount of dissolved copper in the insulating oil, the dielectric loss tangent (tanδ), and the amount of combustible gas (TCG) and hydrogen gas generated in the combustible gas of insulating oil collected from oil-filled cables. Based on the characteristic values measured and calculated during the formation period of organic copper compounds and copper sulfide, it is possible to diagnose the risk of abnormal occurrence in oil-filled cables with high accuracy, thus completing the present invention.
[0010] The present invention provides a diagnostic method for evaluating the degree of risk of abnormality occurring within an oil-filled cable using insulating oil. Step 1 involves taking insulating oil from the oil-filled cable as it is used, measuring the amount of copper dissolved in the insulating oil, the amount of hydrogen gas generated (H2), the dielectric loss tangent (tanδ), and the total amount of combustible gas (TCG), and creating a trend graph based on the obtained measurements, either (A) a trend graph showing the change over time of the dielectric loss tangent (tanδ) and the total amount of combustible gas (TCG), or (B) a trend graph showing the change over time of the amount of copper dissolved in the oil, the dielectric loss tangent (tanδ), and the total amount of combustible gas (TCG). Step 2 involves determining the maximum amount of copper dissolved in the oil based on the measurements obtained in step 1, Step 3 involves determining the amount of decrease from the maximum amount of copper dissolved in the oil, based on the measured values obtained in step 1 and the maximum amount of copper dissolved in the oil determined in step 2. It has, An oil-filled cable whose dielectric loss tangent (tanδ), as shown in the trend graph created in step 1, is in a decreasing phase or has a trend that has decreased to a nearly steady state is evaluated as requiring diagnosis. In the oil-filled cable that has been evaluated as requiring diagnosis, the risk of the aforementioned abnormality occurring is evaluated based on the results of evaluating at least the following characteristic values (a) to (c) based on predetermined reference values. (a) The amount of decrease from the maximum amount of copper dissolved in the oil, (b) Total amount of combustible gas (TCG), and (c) Amount of hydrogen gas generated (H2)
[0011] Furthermore, the present invention relates to a diagnostic method for evaluating the degree of risk of abnormality occurring within an oil-filled cable using insulating oil. The process includes step 1, in accordance with the usage history of the oil-filled cable, taking insulating oil from the cable, measuring the amount of copper dissolved in the insulating oil, the amount of hydrogen gas generated (H2), the dielectric loss tangent (tanδ), and the total amount of combustible gas (TCG), and creating a trend graph showing either (A) the change in dielectric loss tangent (tanδ) and total amount of combustible gas (TCG) over time, or (B) the change in the amount of copper dissolved in the oil, the dielectric loss tangent (tanδ), and the total amount of combustible gas (TCG) over time. An oil-filled cable whose dielectric loss tangent (tanδ), as shown in the trend graph created in step 1, is in a decreasing phase or has a trend that has decreased to a nearly steady state is evaluated as requiring diagnosis. In the oil-filled cable that has been evaluated as requiring diagnosis, the risk of the aforementioned abnormality occurring is evaluated based on the results of evaluating at least the following characteristic values (f) to (i) based on predetermined reference values. (f) Amount of copper dissolved in the insulating oil, (g) Total amount of the above-mentioned combustible gas (TCG), (h) The amount of hydrogen gas generated (H2), and (i) H2 / TCG
[0012] The diagnostic method of the present invention further comprises step 6, which determines tanδ / Cu, the ratio of the dielectric loss tangent (tanδ) to the amount of copper dissolved in the oil, based on the measurement values obtained in step 1. It is preferable to set at least one of the reference values to be different depending on whether tanδ / Cu is greater than or equal to a predetermined value, or whether tanδ / Cu is less than a predetermined value.
[0013] The diagnostic method of the present invention is based on the assumption that the conductors constituting the oil-filled cable react with hydrocarbons and non-hydrocarbon compounds in the insulating oil, dissolving in the insulating oil as copper complexes or copper compounds. These copper complexes then aggregate on the insulating paper of the reinforcing insulating layer in the high-electric field region by dielectrophoresis, acting as a copper catalyst to promote oxidation of the insulating oil and bonding reactions with the copper complexes or copper compounds, thereby generating organic copper compounds, and ultimately copper sulfide. This organic copper compound or copper sulfide then undergoes dielectrophoresis in the high-electric field region, agglomerating and accumulating on the insulating paper. Furthermore, since a linear positive correlation is observed between the dielectric loss tangent (tanδ) and the amount of copper dissolved in the oil of the insulating oil before use of the oil-filled cable, it is assumed that the larger the maximum amount of copper dissolved in the oil, the greater the amount of organic copper compounds and copper sulfide produced.
[0014] In oil-filled cables using insulating oil, a diagnostic method (hereinafter sometimes referred to as the "detailed method") for evaluating the risk of abnormality occurring within the oil-filled cable based on characteristic values (a) to (c) can evaluate the risk of abnormality with high accuracy by utilizing all data accumulated since the oil-filled cable was in operation. More specifically, in the detailed method, the characteristic values (a) the amount of decrease from the maximum amount of copper dissolved in the oil, (b) the total amount of combustible gas (TCG), and (c) the amount of hydrogen gas generated (H2) are comprehensively evaluated based on predetermined standard values, and the risk of abnormality is evaluated based on the results of this evaluation. Furthermore, the amount of copper dissolved in the oil is an indicator of the amount of copper that causes the formation of organic copper compounds and copper sulfide, and is therefore a factor related to the formation of organic copper compounds and copper sulfide. In addition, the total amount of combustible gas (TCG) is an indicator of the increase in dissolved gases in the insulating oil.
[0015] In oil-filled cables using insulating oil, a diagnostic method (hereinafter sometimes referred to as the "simplified method") that evaluates the risk of abnormality occurring within the oil-filled cable based on characteristic values (f) to (i) can evaluate the risk of abnormality with high accuracy even when using limited data from data accumulated since the oil-filled cable was put into operation (measurements taken within a predetermined period from the date of diagnosis to the date the oil-filled cable was laid). More specifically, in the simplified method, the characteristic values (f) amount of copper dissolved in the insulating oil, (g) total amount of combustible gas (TCG), (h) amount of hydrogen gas generated (H2), and (i) H2 / TCG are comprehensively evaluated based on predetermined standard values, and the risk of abnormality is evaluated based on the results of this evaluation. [Effects of the Invention]
[0016] According to the diagnostic method of the present invention, unlike conventional diagnostic methods such as oil gas analysis (diagnosis of trend of gases generated by partial discharge or thermal degradation), diagnosis of the deterioration trend of the electrical properties of insulating oil (tanδ, TCG, volume resistivity, AC withstand voltage measurement), and water intrusion diagnosis (moisture content measurement), the diagnosis is based on the copper sulfide formation mechanism, and therefore, the risk of abnormality can be diagnosed with high accuracy even for oil-filled cables using insulating oil that does not contain dibenzyl disulfide.
[0017] By using a simplified method when utilizing limited data accumulated since the operation of oil-filled cables, and a detailed method when utilizing data accumulated since the operation of oil-filled cables, the risk of malfunction can be evaluated with high accuracy. Therefore, for example, the risk of malfunction can be easily and accurately diagnosed for oil-filled cables that have been in operation for 30 to 40 years. [Brief explanation of the drawing]
[0018] [Figure 1] This figure shows an example of a trend graph illustrating the changes in tanδ and TCG over time. [Figure 2] This is a schematic diagram illustrating how to calculate TCGAve, which is the average value of a trading card game (TCG). [Modes for carrying out the invention]
[0019] The following describes in detail a diagnostic method for evaluating the risk of abnormalities occurring within an oil-filled cable (hereinafter referred to as "OF cable") according to the present invention.
[0020] <<Degradation status of OF cables>> OF cables, if simply using oil-impregnated insulating paper as an insulator, would not satisfy the required characteristics because temperature changes would cause a drop in the insulating oil pressure, leading to the formation of air bubbles in the insulating oil. Therefore, they are designed to withstand high electric field strengths by providing an oil passage inside the conductor (or metal sheath) and constantly applying a pressure above atmospheric pressure to the insulating oil through an externally installed oil tank. The insulation of OF cables is constructed by wrapping tape-shaped insulating paper and impregnating it with insulating oil. In this process, to improve bending characteristics, the insulating paper is usually not overlapped, but rather constructed with evenly spaced gaps.
[0021] Factors that can degrade the insulation performance of OF cables include a decrease in the degree of polymerization of the insulating paper due to overheating, damage, deformation, and collapse of the insulation due to vibration and thermal expansion, negative pressure, oil leakage, and abnormal insulating oil properties. Although OF cables have a margin of safety against AC voltage, if defects exist due to displacement or damage of the insulating paper caused by core misalignment, etc., the intrusion of overvoltage can cause partial discharge at the defective area, generating gas, and if this is repeated, it may occur as voids at the defective area. Furthermore, since voids have extremely low dielectric strength, it is possible that partial discharge will continue when AC voltage is applied.
[0022] ≪Mechanism of copper sulfide formation in OF cables≫ The conventional mechanism by which copper sulfide is formed in insulating oil with added DBDS is thought to be as follows: DBDS reacts with the copper in the conductor, the DBDS-copper complex diffuses into the insulating oil, the DBDS-copper complex diffused in the oil is adsorbed onto the insulating paper, and then decomposes due to thermal energy to produce copper sulfide.
[0023] On the other hand, in this invention, it is assumed that the formation of copper sulfide in OF cables is due to the following mechanism: (i) the conductor and insulating oil react, (ii) the copper complex or copper compound dissolves in the insulating oil, (iii) the dissolved copper complex or copper compound aggregates in a high-electric field region by dielectrophoresis, (iv) the copper catalyst promotes the oxidation of the insulating oil and the bonding reaction with the copper complex or copper compound, generating a polymeric organocopper compound, and (v) the generated organocopper compound further aggregates in the high-electric field region by dielectrophoresis, and the copper complex, copper compound or organocopper compound aggregated in the high-electric field region reacts with sulfur components contained in the insulating paper or insulating oil to produce copper sulfide. Furthermore, in this invention, it is assumed that the sulfur components that react with the copper complex, copper compound or organocopper compound are not limited to components added to the insulating oil, such as DBDS, but also include sulfur components derived from sulfur compounds used in the manufacture of insulating paper, and sulfur components derived from petroleum, which is a raw material for insulating oil.
[0024] Furthermore, the above mechanism is presumed to involve the reaction of copper complexes or copper compounds with insulating oil to produce polymeric organocopper compounds. These organocopper compounds are large solid substances with high molecular weights, and are thought to aggregate by dielectrophoresis in high-electric-field regions, accumulating in cable cores and other areas, causing a decrease in insulation performance and dielectric breakdown, similar to copper sulfide.
[0025] In other words, the copper sulfide formation mechanism according to the present invention is based on the assumption that even in the case of insulating oil without added sulfur compounds such as DBDS, the reaction rate is very slow, but organocopper compounds and copper sulfide are formed over time, and it is estimated that the three conditions of copper + insulating oil + high electric field are necessary for the formation of organocopper compounds and copper sulfide.
[0026] ≪Diagnostic method based on the mechanism of copper sulfide formation≫ According to the copper sulfide formation mechanism in OF cables described above, (ii) when copper complexes or copper compounds dissolve in the insulating oil, the amount of copper dissolved in the oil and the dielectric loss tangent (tanδ) of the insulating oil increase. Subsequently, (iii) the amount of dissolved copper reaches its maximum when the copper complexes or copper compounds aggregate in the high-electric field region. Eventually, (iv) the amount of copper dissolved in the oil and the dielectric loss tangent (tanδ) of the insulating oil decrease with the formation of organocopper compounds and (v) copper sulfide.
[0027] On the other hand, the gases generated during the formation of copper complexes, organocopper compounds, and copper sulfide are absorbed by the insulating oil, increasing the gas concentration in the oil and thus increasing the measured values of hydrogen gas (H2) and total combustible gas (TCG) in the oil.
[0028] Figure 1 is an example of a trend graph showing the increase or decrease in the dielectric loss tangent (tanδ) of the insulating oil and the total amount of combustible gas (TCG) in the oil over time, based on the copper sulfide formation mechanism in the OF cable described above.
[0029] Here, the trend graphs of dielectric loss tangent (tanδ) and total combustible gas (TCG) correlate with the trend graphs of dissolved copper in oil and total combustible gas (TCG). That is, from the trend graphs of dielectric loss tangent (tanδ) and total combustible gas (TCG) (Figure 1), the "decrease" period of these characteristic values corresponds to the formation period of organocopper compounds and copper sulfide (which is abbreviated as "copper sulfide formation period" in Figure 1). It can be estimated that if these characteristic values (absolute values) are large, the amount of dissolved copper in oil that becomes organocopper compounds and copper sulfide is large, and therefore the amount of organocopper compounds and copper sulfide produced will be large. Therefore, in (A) a trend graph showing the change over time between the dielectric loss tangent (tanδ) and the total amount of combustible gas (TCG), or (B) a trend graph showing the change over time between the amount of copper dissolved in oil, the dielectric loss tangent (tanδ), and the total amount of combustible gas (TCG), it is possible to estimate the formation status of organocopper compounds and copper sulfide within the OF cable from the maximum value of the dielectric loss tangent (tanδ).
[0030] Prior tests have confirmed that the approximate equation for the linear relationship between the amount of copper dissolved in oil and the dielectric loss tangent can be expressed by a linear equation. Based on these findings, the inventors have confirmed that the maximum amount of copper dissolved in oil can be estimated from the maximum value of tanδ using the following equation (1). [Cu] max =(tanδ max -tanδ0)×{[Cu] / (tanδ-tanδ0)}···(1) In the above formula (1), [Cu] max This is the maximum amount of copper dissolved in oil, and tanδ max is the maximum value derived from the trend graph of the dielectric loss tangent (tanδ), tanδ0 is the dielectric loss tangent (tanδ) value of new insulating oil, and tanδ and [Cu] are the dielectric loss tangent (tanδ) and dissolved copper content in the insulating oil, respectively, of the insulating oil sampled at a certain point in time from the actual equipment after it has been put into use.
[0031] According to equation (1) above, the dielectric loss tangent value of new insulating oil (tanδ0) and the past maximum value of the dielectric loss tangent (tanδ) of insulating oil sampled from actual equipment are given by... max From the dielectric loss tangent (tanδ) and the amount of copper dissolved in the oil at a certain point in time (for example, the most recent measurement), the maximum amount of copper dissolved in the oil in the actual equipment [Cu] can be easily determined. max This allows for the calculation of the formation status of organocopper compounds and copper sulfide, thereby enabling estimation of their formation. In other words, if the maximum amount of copper dissolved in the oil is large, it can be estimated that a large amount of copper dissolved in the oil will be converted into organic copper compounds and copper sulfide, and therefore the amount of organic copper compounds and copper sulfide produced will be large. Also, if the difference between the maximum amount of copper dissolved in the oil and the amount of copper dissolved in the oil at the most recent measurement (the decrease from the maximum amount of copper dissolved in the oil) is large, it can be estimated that a large amount of organic copper compounds and copper sulfide have already been produced at the time of that measurement.
[0032] <Diagnosis Method> The diagnostic method of the present invention will be described in detail below. In the diagnostic method of the present invention for evaluating the risk of abnormal occurrence in an oil-filled cable, as step 1 of the simplified method and the detailed method, the amount of dissolved copper in the insulating oil, the amount of hydrogen gas generated (H2), the dielectric loss tangent (tanδ), and the total amount of combustible gas (TCG) are measured from the insulating oil sampled from the oil-filled cable. Based on each measured value, a trend graph is created showing either (A) the change over time of the dielectric loss tangent (tanδ) and the total amount of combustible gas (TCG), or (B) the change over time of the amount of dissolved copper in the oil, the dielectric loss tangent (tanδ), and the total amount of combustible gas (TCG). Specifically, combustible gases include hydrogen, carbon monoxide, methane, ethane, and acetylene.
[0033] When diagnosing the risk of malfunction using only measurements taken within a specified period from the date of diagnosis to the date the oil-filled cable was installed, the simplified method described below will be used to diagnose the risk of malfunction. When diagnosing the risk of malfunction using not only measurements taken within a specified period from the date of diagnosis, but also measurements taken before that period, the detailed method described below will be used to diagnose the risk of malfunction. This allows for the selection of the most suitable diagnostic method depending on the amount of accumulated data available. The "specified period" can be set appropriately according to the number of years elapsed since the date the oil-filled cable was installed. An example of the "specified period" is (number of years elapsed since the date the oil-filled cable was installed) × 0.25. The simplified and detailed methods will be explained in detail below.
[0034] (1) Simple method In the simplified method, the equipment risk is diagnosed based on the formation status of organic copper compounds and copper sulfide. Specifically, the characteristic values of (f) the amount of copper dissolved in insulating oil, (g) the total amount of combustible gas (TCG), (h) the amount of hydrogen gas generated (H2), and (i) H2 / TCG are comprehensively evaluated based on predetermined standard values, and the risk of equipment malfunction is diagnosed based on the evaluation results according to specific diagnostic criteria. Note that one standard value may be set for (f) the amount of copper dissolved in insulating oil, or two or more may be set.
[0035] In the simple method, furthermore, the average value TCG of the total amount of combustible gas (TCG) during the formation period of the organocopper compound and copper sulfide shown in the trend graph Ave Step 4 of obtaining and the average value H of the amount of hydrogen gas generated (H2) during the formation period of the organocopper compound and copper sulfide shown in the trend graph 2Ave Step 5 of obtaining, wherein the (g) total amount of combustible gas (TCG) is the average value TCG of the total amount of combustible gas (TCG) Ave and the (h) amount of hydrogen gas generated (H2) is the average value H of the amount of hydrogen gas generated (H2) 2Ave and the (i) H2 / TCG is H 2Ave / TCG Ave It is preferable that it is. Thus, as the (g) total amount of combustible gas (TCG), the average value TCG of the total amount of combustible gas (TCG) Ave is used, as the (h) amount of hydrogen gas generated (H2), the average value H of the amount of hydrogen gas generated (H2) 2Ave is used, and as the (i) H2 / TCG, H 2Ave / TCG Ave is used, whereby a value close to the characteristics of the actual change over time can be obtained, and the diagnostic accuracy of the risk of abnormal occurrence can be improved.
[0036] FIG. 2 is a diagram showing how to obtain the average value TCG of the total amount of combustible gas (TCG), and the average value TCG Ave and the average value TCG AveThis is calculated using the concept of interval integration. For example, as shown in Figure 2, if the total amount of combustible gas (TCG) is measured at four points in time: A (year the oil-filled cable was laid), B, C, and D, then the intervals are divided at the midpoint between A and B (2.5 years after 2010), the midpoint between B and C (1.5 years after 2015), and the midpoint between C and D (1.0 year after 2018). Furthermore, the total amount of combustible gas (TCG) in A shall be assumed to be the period from A to the midpoint between A and B (2.5 years), the total amount of combustible gas (TCG) in B shall be assumed to be the period from the midpoint between A and B to the midpoint between B and C (2.5 years + 1.5 years = 4.0 years), the total amount of combustible gas (TCG) in C shall be assumed to be the period from the midpoint between B and C to the midpoint between C and D (1.5 years + 1.0 year = 2.5 years), and the total amount of combustible gas (TCG) in D shall be assumed to be the period from the midpoint between C and D to D (1.0 year). Ave This is calculated by dividing the sum of the areas of each section set as described above by the number of years from A to D. For example, in Figure 2, TCG Ave This can be calculated using the following formula (2). TCG Ave (ppm) ={A(50ppm×2.5 years)+B(100ppm×4.0 years)+C(250ppm×2.5 years)+D(200ppm×1.0 years)} / 10.0 years =135 ppm (2)
[0037] The above TCG Ave To explain the method of determining this in general terms, the measurement years are N1, N2, ...N m Toshi (however, N1 is the year the oil-filled cable was laid, N m (where is the year the last measurement was taken), N1, N2, ...N m The TCG measurements in each are TCG1, TCG2, ...TCG m In that case, TCG Ave This can be calculated using the following formula (3).
number
[0038] Average value of hydrogen gas generation (H2) 2Ave Regarding TCG Ave Similarly, we can find it by following the concept of interval integration. H 2Ave To explain the method of determining this in general terms, the measurement years are N1, N2, ...N m Toshi (however, N1 is the year the oil-filled cable was laid, N m (where is the year the last measurement was taken), N1, N2, ...N m The measured values of H2 in each location are, 2, 1 H 2, 2 ,···H 2, m When H 2Ave This can be calculated using the following formula (4).
number
[0039] In the simplified method, it is preferable to further evaluate the risk of abnormal occurrence based on the results of evaluating the characteristic values (f) to (i) and characteristic value (j) and the number of years elapsed since the installation of the oil-filled cable, based on predetermined reference values. By diagnosing the risk of abnormal occurrence using characteristic values (f) to (j) in this way, the values become closer to the actual characteristics of changes over time, and the accuracy of diagnosing the risk of abnormal occurrence can be improved.
[0040] In addition, the simplified method further includes step 6 to determine tanδ / Cu, which is the ratio of the dielectric loss tangent (tanδ) to the amount of copper dissolved in the oil. It is preferable to set at least one reference value differently depending on whether tanδ / Cu is greater than or equal to a predetermined set value or less than a predetermined set value. In this case, all of the reference values (f) to (j) above may be different depending on whether tanδ / Cu is greater than or equal to a predetermined set value or less than a predetermined set value, or some of the reference values among (f) to (j) above may be different. Prior investigations have shown that the reference values of characteristic values (f) to (j) may change depending on whether tanδ / Cu is greater than or equal to a specific set value or less than a specific set value. The reason for this is that when tanδ / Cu is greater than the set value, organocopper compounds and copper sulfide have already been generated in many parts of the equipment at that point. However, subsequent comparative investigation of the equipment's deterioration location and the insulating oil's characteristic values revealed that when deterioration occurred from the outside to the inside of the equipment, tanδ / Cu was greater than the set value. Furthermore, when comparing the deterioration location being outside the equipment with that from the outside to the inside, it was confirmed that TCG and the amount of decrease tended to be lower when the deterioration occurred from the outside to the inside. This is thought to be because the reference values of characteristic values (f) to (j) change as a result. Therefore, by setting at least one reference value among characteristic values (f) to (j) different depending on whether tanδ / Cu is above the set value or below the set value, the risk of abnormal occurrence can be diagnosed with higher accuracy.
[0041] Table 1 below shows an example where different standard values are set for tanδ / Cu of 0.9 or higher and for values less than 0.9. In Table 1 below, (f) Two standard values are set for the amount of dissolved copper in insulating oil, and (g) The average value of the total combustible gas (TCG) is used. Ave Using this, the average value of the hydrogen gas generation amount (H2) is used as (h) hydrogen gas generation amount (H2). 2Ave Using (i) H2 / TCG, 2Ave / TCG Ave I used it.
[0042] (Reference values for characteristic values (f) to (i)) [Table 1] In one example of the present invention, characteristic values (f) to (j) are checked to see if they are above or below the reference values listed in Table 1 above, and the results of the checks for each characteristic value are comprehensively evaluated according to Table 2 below to diagnose the risk of abnormal occurrence. Note that the reference values listed in Table 1 above are examples, and suitable reference values can be set as appropriate depending on the type of oil-filled cable, the operating environment, etc.
[0043] (Diagnostic criteria for the risk of abnormal occurrence) Of the ranks A to D diagnosed according to the criteria shown in Table 2 below, rank A is diagnosed as having a "high" risk of abnormal occurrence, rank B as having a "medium" risk of abnormal occurrence, rank C as having a "low" risk of abnormal occurrence, and rank D as having a "very low" risk of abnormal occurrence. [Table 2]
[0044] (Diagnostic criteria for the risk of abnormal occurrence) By evaluating and ranking the level of risk in the order described above, the level of risk of the equipment can be determined relatively easily, and the results are consistent with those obtained from dismantling surveys of oil-filled cables using insulating oil. Note that the items listed in Table 2 above are just examples, and the appropriate items can be set as needed depending on the type of oil-filled cable, the operating environment, etc.
[0045] (2) Detailed method In the detailed method, similar to the simplified method described in (1) above, the values of each item—(a) the decrease from the maximum amount of copper dissolved in the oil, (b) the total amount of combustible gas (TCG), and (c) the amount of hydrogen gas generated (H2)—are comprehensively evaluated based on predetermined standard values, and the degree of risk of equipment malfunction is diagnosed based on the evaluation results according to specific diagnostic criteria.
[0046] The detailed method further involves the average value of total combustible gas (TCG) during the formation phase of organocopper compounds and copper sulfide, as shown in the trend graph.Ave Step 4 to determine the average amount of hydrogen gas (H2) generated during the formation phase of organocopper compounds and copper sulfide, as shown in the trend graph. 2Ave (b) The total amount of combustible gas (TCG) is the average value of the total amount of combustible gas (TCG) Ave (c) The amount of hydrogen gas generated (H2) is the average value of the amount of hydrogen gas generated (H2) H 2Ave It is preferable that (b) the average value of the total amount of combustible gas (TCG) is used as the total amount of combustible gas (TCG) Ave Using (c) the average value of the hydrogen gas generation amount (H2) as H 2Ave By using this method, the numerical values become closer to the actual characteristics of changes over time, improving the accuracy of diagnosing the risk of abnormal occurrence.
[0047] In the detailed method, in step 2, it is preferable to determine the maximum amount of copper dissolved in the oil using the following formula (1) based on the measurement values obtained in step 1. However, in the following formula (1), [Cu] max This is the maximum amount of copper dissolved in oil, and tanδ max is the maximum value of the dielectric loss tangent (tanδ) derived from the trend graph created in step 1, tanδ0 is the dielectric loss tangent (tanδ) of the insulating oil (new insulating oil) before the oil-filled cable is put into use, and tanδ and [Cu] are the dielectric loss tangent (tanδ) and the amount of dissolved copper in the oil of the insulating oil at a certain point in time after the oil-filled cable is put into use, respectively. The certain point in time after the oil-filled cable is put into use is preferably the most recent measurement point (when performing the diagnosis), but it may also be any past measurement point during the formation period of the organocopper compound and copper sulfide. [Cu] max =(tanδ max -tanδ0)×{[Cu] / (tanδ-tanδ0)}···(1) Maximum amount of copper dissolved in oil [Cu] max A larger value indicates a greater amount of copper dissolved in the oil, which then forms organocopper compounds and copper sulfide. Therefore, it can be estimated that a large amount of organocopper compounds and copper sulfide are produced.
[0048] Next, in step 3 of the detailed method, the amount of copper dissolved in the insulating oil at a certain point in time after the formation of organocopper compounds and copper sulfide, and the maximum amount of copper dissolved, are derived from the trend graph of total combustible gas (TCG) created in step 1. max ) difference ([Cu] max The decrease from the maximum amount of copper dissolved in the oil is calculated as -[Cu]). Note that the point in time after the formation of organocopper compounds and copper sulfide is the most recent measurement point (when performing the diagnosis) (the same applies below). If the amount of copper dissolved in the oil at a point in time after the formation of organocopper compounds and copper sulfide has decreased significantly from the maximum amount of copper dissolved in the oil (the decrease is large), it can be estimated that a large amount of organocopper compounds and copper sulfide have already been formed at that point.
[0049] In the detailed method, for oil-filled cables that have been evaluated as requiring diagnosis, it is preferable to evaluate the risk of abnormality based on the results of evaluating characteristic values (a) to (c), characteristic value (d) the amount of copper dissolved in the insulating oil, and characteristic value (e) the number of years elapsed from the point in time when the dielectric loss tangent (tanδ) shown in the trend graph created in step 1 began to decrease until the point in time when the decrease ends, each based on a predetermined reference value. By diagnosing the risk of abnormality using characteristic values (a) to (e) in this way, the numerical value becomes closer to the actual characteristics of changes over time, and the accuracy of diagnosing the risk of abnormality can be improved.
[0050] Furthermore, the detailed method further includes step 6 to determine tanδ / Cu, which is the ratio of the dielectric loss tangent (tanδ) to the amount of copper dissolved in the oil. It is preferable to set at least one reference value differently depending on whether tanδ / Cu is greater than or equal to a predetermined value or less than a predetermined value. In this case, all of the reference values (a) to (e) above may be different depending on whether tanδ / Cu is greater than or equal to a predetermined value or less than a predetermined value, or some of the reference values among (a) to (e) may be different. Prior investigations have shown that the reference values of characteristic values (a) to (e) may change depending on whether tanδ / Cu is greater than or equal to a specific value or less than a specific value. The reason for this is that when tanδ / Cu is greater than the set value, organocopper compounds and copper sulfide have already been generated in many parts of the equipment at that point. However, subsequent comparative investigation of the equipment's deterioration location and the insulating oil's characteristic values revealed that deterioration occurred inside the equipment when tanδ / Cu was greater than the set value. Furthermore, when comparing the deterioration location outside the equipment with that from the outside to the inside, it was confirmed that TCG and the amount of decrease tended to be lower when the deterioration progressed from the outside to the inside. This is thought to be because the reference values of characteristic values (a) to (e) change as a result. Therefore, by setting at least one reference value among characteristic values (a) to (e) different depending on whether tanδ / Cu is above the set value or below the set value, the risk of abnormal occurrence can be diagnosed with higher accuracy.
[0051] Table 3 below shows an example where different standard values are set for tanδ / Cu of 0.9 or higher and for values less than 0.9. Note that in Table 3 below, (b) Total combustible gas (TCG) is the average value of the total combustible gas (TCG) Ave Using (c) the average value of the hydrogen gas generation amount (H2) as H 2Ave I used it. (Reference values for characteristic values (a) to (e)) [Table 3] In one example of the present invention, characteristic values (a) to (e) are checked to see if they are above or below the reference values listed in Table 3 above, and the results of the checks for each characteristic value are comprehensively evaluated according to Table 4 below to diagnose the risk of abnormal occurrence. Note that the reference values listed in Table 3 above are examples, and suitable reference values can be set as appropriate depending on the type of oil-filled cable, the operating environment, etc.
[0052] Of the ranks A to D diagnosed according to the criteria shown in Table 4 below, rank A is diagnosed as having a "high" risk of abnormal occurrence, rank B as having a "medium" risk of abnormal occurrence, rank C as having a "low" risk of abnormal occurrence, and rank D as having a "very low" risk of abnormal occurrence. [Table 4] (Diagnostic criteria for the risk of abnormal occurrence) By evaluating and ranking the level of risk in the order described above, the level of risk of the equipment can be determined relatively easily, and the results are consistent with those obtained from dismantling surveys of oil-filled cables using insulating oil. Note that the items listed in Table 4 above are just examples, and the appropriate items can be set as needed depending on the type of oil-filled cable, the operating environment, etc. [Examples]
[0053] Next, we will specifically describe the results of confirming the effectiveness of the diagnostic method according to the present invention, but the present invention is not limited to the following examples.
[0054] (1) Confirmation of the effectiveness of this diagnostic method For the actual equipment (120 OF cables), the estimated diagnostic results obtained based on the diagnostic methods of the present invention (simplified method and detailed method) were compared with the results of the dismantling survey. The results are shown in Table 5. The estimated diagnostics based on the diagnostic methods of the present invention and the dismantling survey were performed using the following methods, respectively.
[0055] <Estimation diagnosis based on the diagnostic method of the present invention> First, for the sample oils taken from each actual facility, the amount of dissolved copper in the insulating oil, the amount of hydrogen gas generated (H2), the dielectric loss tangent (tanδ), and the total amount of combustible gas (TCG) were measured using the following measurement methods. Based on the obtained measurement values, trend graphs showing the changes in the dielectric loss tangent (tanδ) and the total amount of combustible gas (TCG) over time were created (Step 1 of the simplified or detailed method).
[0056] Furthermore, of the actual equipment (120 OF cables), 64 OF cables were assessed using only measurements taken over a predetermined period (elapsed years × 0.25 years) relative to the number of years since the cable was laid. These 64 OF cables were assessed using the simplified method, while 56 OF cables were assessed using the detailed method if there were measurements taken beyond the predetermined period relative to the number of years since the cable was laid, using all measurements.
[0057] Next, for the 64 OF cables subject to diagnosis using the simplified method, the average value of (g) total combustible gas (TCG) was calculated from the total amount of combustible gas (TCG) and hydrogen gas generation amount (H2) measured in step 1 above. Ave (h) Average value of hydrogen gas generation (H2) 2Ave (i)H 2Ave / TCG Ave The following characteristics were obtained for each actual piece of equipment: (f) amount of dissolved copper in insulating oil, and (g) the average value of total combustible gas (TCG). Ave (h) Average value of hydrogen gas generation (H2) 2Ave , (i)H 2Ave / TCG Ave (j) The number of years elapsed since the installation of the oil-filled cable was checked to see if it was above or below the predetermined standard value in Table 1 above, and the risk of malfunction of the equipment was diagnosed based on the diagnostic criteria in Table 2 above from the results of this check.
[0058] Furthermore, for the 56 OF cables subject to detailed diagnosis, the average value of the total combustible gas (TCG) was calculated from the total combustible gas (TCG), hydrogen gas generation (H2), dielectric loss tangent (tanδ), and amount of dissolved copper in the insulating oil measured in step 1 above. Ave , the average value of hydrogen gas generation (H2) 2Ave Furthermore, the maximum amount of copper dissolved in the oil was calculated based on the above formula (1) (steps 2, 4, and 5 of the detailed method), and the decrease from the maximum amount of copper dissolved in the oil was calculated from the maximum amount of copper dissolved in the oil obtained in step 2 (step 3 of the detailed method). After this, the characteristic values obtained for each actual facility were (a) decrease from the maximum amount of copper dissolved in the oil, (d) amount of copper dissolved in the insulating oil, and (b) average value of total combustible gas (TCG) TCG. Ave (e) The number of years elapsed from the point in time when the dielectric loss tangent (tanδ) shown in the trend graph created in step 1 began to decrease (the point in time when the dielectric loss tangent (tanδ) showed a maximum value) to the point in time when the decrease ended, and (c) the average value of hydrogen gas generation (H2) 2Ave The system was checked to determine whether the values were above or below the predetermined standard values in Table 3, and based on the results of this check, the risk of malfunction in the equipment was diagnosed based on the diagnostic criteria in Table 4.
[0059] (Measurement conditions) The above measurements were performed using the following procedure. • Measurement of dielectric loss tangent (tanδ) 50 ml of sample oil taken from each actual facility was placed in a liquid electrode, heated to 80°C, and measured using a tanδ analyzer after applying 1000 V.
[0060] • Measurement of hydrogen gas generation (H2) and total combustible gas (TCG) Oil sampling syringes (200 ml) containing sample oil collected from each actual facility were set in a gas sampling device, and gases in the oil (oxygen, nitrogen, hydrogen, methane, ethane, ethylene, acetylene, sulfur hexafluoride, carbon monoxide, and carbon dioxide) were separated, extracted, and analyzed using a gas chromatograph. The total amount of combustible gas (TCG) is the sum of the amounts of each gas analyzed: hydrogen, methane, ethane, ethylene, acetylene, and carbon monoxide.
[0061] • Measurement of the amount of copper dissolved in insulating oil Sample oils collected from each actual facility were diluted 10-fold with xylene to prepare a prepared solution, and the amount of dissolved copper (mg) in the oil per 1 kg of insulating oil was analyzed using an inductively coupled plasma (ICP) emission spectrometer. For the preparation of the calibration curve standard solution, a commercially available oily copper-containing standard solution was used, which was then diluted sequentially with blank oil and xylene.
[0062] <Demolition Survey> The dismantling survey was conducted by visually inspecting the surface and interior of the reinforcing insulating paper of the actual equipment, and the innermost, outermost, and innermost layers of the cable insulating paper, to determine the formation patterns and locations of the black areas on the insulating paper, which are the areas where organic copper compounds and copper sulfide are formed. The results were evaluated from A to D based on the following diagnostic criteria. Furthermore, to confirm the formation of organocopper compounds and copper sulfide, electron microscopy and X-ray fluorescence analysis were used to identify locations on the insulating paper where both copper (Cu) and sulfur (S) were detected in the blackened areas. At these identified locations, organocopper compounds were confirmed by detecting absorption peaks of insulating oil, oxidation products, and sulfur compounds in the infrared absorption spectrum using Fourier transform infrared spectrophotometer (FTIR), and copper sulfide was confirmed by detecting the Raman spectrum of copper sulfide using micro-Raman spectrometer.
[0063] <Diagnostic Criteria> A: This refers to a laminated state in which reinforcing insulating paper or cable insulating paper with black areas exceeding discharge marks, dots, or streaks are continuously laminated in the thickness direction, resulting in a dangerous state in terms of insulating performance. B: The reinforcing insulating paper or cable insulating paper has black areas that exceed discharge marks, dots, or streaks, and is continuously laminated in the thickness direction, resulting in a laminated state that affects the insulating performance. C: The reinforcing insulating paper or cable insulating paper has spot-like or streak-like discoloration only near the outermost layer, and the impact on insulating performance is small. D: No black areas.
[0064] Table 5 below shows a comparison of the diagnostic results obtained using the diagnostic method of the present invention and the results obtained from the dismantling survey. [Table 5]
[0065] As shown in Table 5, for the 64 cables evaluated using the simplified method, there were 5 and 11 facilities where the diagnostic results based on the present invention's diagnostic method were underestimated and overestimated compared to the actual facility dismantling survey results. However, for the remaining facilities, the diagnostic results of the present invention were in agreement with the dismantling survey results, resulting in a high accuracy rate of 75.0%. Similarly, for the 56 cables evaluated using the detailed method, there were 4 and 2 facilities where the diagnostic results based on the present invention's diagnostic method were underestimated and overestimated compared to the actual facility dismantling survey results. However, for the remaining facilities, the diagnostic results of the present invention were in agreement with the dismantling survey results, resulting in a very high accuracy rate of 89.3%. Furthermore, looking at the total (120 cables) evaluated using both the simplified and detailed methods, the diagnostic results of the present invention were in agreement with the dismantling survey results for 98 facilities, resulting in a very high accuracy rate of 81.7%. These results confirm that the diagnostic method of the present invention can obtain results that correspond to the dismantling survey results of the actual facility. Furthermore, according to the diagnostic method of the present invention, there is no need to dismantle the actual equipment and conduct tests as in dismantling surveys. Each measurement and evaluation can be performed simply by collecting test oil from the OF cable, and it has been confirmed that the degree of risk of the actual equipment can be diagnosed relatively easily.
Claims
1. A diagnostic method for evaluating the risk of abnormalities occurring within an oil-filled cable using insulating oil, Depending on the usage history of the oil-filled cable, the insulating oil is collected from the oil-filled cable, and the amount of copper dissolved in the insulating oil and the amount of hydrogen gas generated (H) are determined. ２ Step 1 involves measuring the dielectric loss tangent (tanδ) and total combustible gas (TCG), and based on the obtained measurements, creating either (A) a trend graph showing the change over time between the dielectric loss tangent (tanδ) and total combustible gas (TCG), or (B) a trend graph showing the change over time between the amount of copper dissolved in oil, the dielectric loss tangent (tanδ), and total combustible gas (TCG). Step 2 involves determining the maximum amount of copper dissolved in oil based on the measurements obtained in step 1, Step 3 involves determining the decrease in the amount of copper dissolved in the oil from the maximum amount of copper dissolved in the oil, based on the measured values obtained in step 1 and the maximum amount of copper dissolved in the oil determined in step 2. Step 4 involves determining the average value of the total amount of combustible gas (TCG) during the formation period of the organic copper compound and copper sulfide, which occurs in the trend graph during the formation period of the organic copper compound and copper sulfide, and calculating the TCG Ave, which is the period during which the amount of dissolved copper in the oil or the dielectric loss tangent (tanδ) decreases after reaching a maximum value. Step 5 involves determining the average value H₂Ave of the amount of hydrogen gas generated (H₂) during the formation phase of the organocopper compound and copper sulfide shown in the trend graph, It has, An oil-filled cable whose dielectric loss tangent (tanδ), as shown in the trend graph created in step 1, is decreasing or has a trend that has decreased and then reached a nearly steady state, is evaluated as requiring diagnosis. In step 2, The maximum amount of copper dissolved in the oil is determined by the following formula (1): [Cu] max = (tan δ max - tan δ 0 ) x {[Cu] / (tan δ - tan δ 0 )}...(1) (However, in formula (1) above, [Cu] max is the maximum amount of copper dissolved in the oil, tanδ max is the maximum value derived from the trend graph of the dielectric loss tangent (tanδ) created in step 1, tanδ 0 is the value of the dielectric loss tangent (tanδ) of the insulating oil (new insulating oil) before the start of use of the oil-filled cable, and tanδ and [Cu] are the values of the dielectric loss tangent (tanδ) of the insulating oil and the amount of copper dissolved in the oil at a certain point in time after the start of use of the oil-filled cable, respectively.) A diagnostic method characterized by evaluating the risk of abnormality occurring in an oil-filled cable that has been evaluated as requiring diagnosis, based on the results of evaluating at least the following characteristic values (a) to (c) based on predetermined reference values. (a) The amount of decrease in the amount of copper dissolved in the oil from the maximum amount of copper dissolved in the oil, (b) Total amount of combustible gas (TCG), and (c) Amount of hydrogen gas generated (H ２ ) The decrease in the amount of copper dissolved in the oil from the maximum amount of copper dissolved in the oil is the difference between the maximum amount of copper dissolved in the oil and the amount of copper dissolved in the oil at a certain point in time. The above (b) Total amount of combustible gas (TCG) is the average value of the total amount of combustible gas (TCG), TCG Ave. The total amount of combustible gas (TCG) mentioned above is the total amount of each combustible gas analyzed. The average value of the total combustible gas (TCG) TCG Ave is calculated using the following formula (3): [Math 1] (However, in formula (3) above, N1, N2, ... Nm are the measurement years (where N1 is the year the oil-filled cable was laid and Nm is the year the last measurement was taken), and TCG1, TCG2, ... TCGm are the measured values of TCG in N1, N2, ... Nm.) The above (c) hydrogen gas generation amount (H2) is the average value of the hydrogen gas generation amount (H2) H2Ave, The average value of the hydrogen gas generation amount (H₂) H₂Ave is calculated using the following formula (4). [Math 2] (However, in formula (4) above, N1, N2, ... Nm are the measurement years (where N1 is the year the oil-filled cable was laid and Nm is the year the last measurement was taken), and H2,1, H2,2, ... H2,m are the measured values of H2 in N1, N2, ... Nm.)
2. The diagnostic method according to claim 1, characterized in that, in the oil-filled cable that has been evaluated as requiring diagnosis, the risk of the abnormality occurring is evaluated based on the results of evaluating the characteristic values (a) to (c) and at least one of the characteristic values (d) and (e) below, each based on a predetermined reference value. (d) Amount of copper dissolved in the insulating oil, (e) The number of years elapsed from the point in time when the dielectric loss tangent (tanδ) shown in the trend graph created in step 1 began to decrease until the point in time when the decrease ended.
3. Furthermore, the process includes a step 6 to determine tanδ / Cu, which is the ratio of the dielectric loss tangent (tanδ) to the amount of copper dissolved in the oil, based on the measurements obtained in step 1. The diagnostic method according to claim 1 or 2, characterized in that at least one of the reference values is set to be different when tanδ / Cu is greater than or equal to a preset value and when tanδ / Cu is less than a preset value.
4. A diagnostic method for evaluating the risk of abnormalities occurring within an oil-filled cable using insulating oil, Depending on the usage history of the oil-filled cable, the insulating oil is collected from the oil-filled cable, and the amount of copper dissolved in the insulating oil and the amount of hydrogen gas generated (H) are determined. ２ Step 1 involves measuring the dielectric loss tangent (tanδ) and total combustible gas (TCG), and based on the obtained measurements, creating either (A) a trend graph showing the change over time between the dielectric loss tangent (tanδ) and total combustible gas (TCG), or (B) a trend graph showing the change over time between the amount of copper dissolved in oil, the dielectric loss tangent (tanδ), and total combustible gas (TCG). Step 4 involves determining the average value of the total amount of combustible gas (TCG) during the formation period of the organic copper compound and copper sulfide, which occurs in the trend graph during the formation period of the organic copper compound and copper sulfide, and calculating the TCG Ave, which is the period during which the amount of dissolved copper in the oil or the dielectric loss tangent (tanδ) decreases after reaching a maximum value. Step 5 involves determining the average value H₂Ave of the amount of hydrogen gas generated (H₂) during the formation phase of the organocopper compound and copper sulfide shown in the trend graph, It has, An oil-filled cable whose dielectric loss tangent (tanδ), as shown in the trend graph created in step 1, is decreasing or has a trend that has decreased and then reached a nearly steady state, is evaluated as requiring diagnosis. A diagnostic method characterized by evaluating the risk of abnormality occurring in an oil-filled cable that has been evaluated as requiring diagnosis, based on the results of evaluating at least the following characteristic values (f) to (i) based on predetermined reference values. (f) Amount of copper dissolved in the insulating oil, (g) Total amount of the combustible gas (TCG), (h) Amount of hydrogen gas generated (H ２ ), and (i)H ２ / TCG The above (g) Total amount of combustible gas (TCG) is the average value of the total amount of combustible gas (TCG), TCG Ave. The total amount of combustible gas (TCG) mentioned above is the total amount of each combustible gas analyzed. The average value of the total combustible gas (TCG) TCG Ave is calculated using the following formula (3): [Math 3] (However, in formula (3) above, N1, N2, ... Nm are the measurement years (where N1 is the year the oil-filled cable was laid and Nm is the year the last measurement was taken), and TCG1, TCG2, ... TCGm are the measured values of TCG in N1, N2, ... Nm.) The above (h) hydrogen gas generation amount (H2) is the average value of the hydrogen gas generation amount (H2) H2Ave, The average value of the hydrogen gas generation amount (H₂) H₂Ave is calculated using the following formula (4): [Math 4] (However, in formula (4) above, N1, N2, ... Nm are the measurement years (where N1 is the year the oil-filled cable was laid and Nm is the year the last measurement was taken), and H2,1, H2,2, ... H2,m are the measured values of H2 in N1, N2, ... Nm.) The above (i) H2 / TCG is H2Ave / TCGAve.
5. The diagnostic method according to claim 4, characterized in that the risk of the abnormality occurring is evaluated based on the results of evaluating the characteristic values (f) to (i) and characteristic value (j), the number of years elapsed since the date the oil-filled cable was laid, based on a predetermined standard value.
6. Furthermore, the process includes a step 6 to determine tanδ / Cu, which is the ratio of the dielectric loss tangent (tanδ) to the amount of copper dissolved in the oil, based on the measurements obtained in step 1. The diagnostic method according to claim 4 or 5, characterized in that at least one of the reference values is set to be different when tanδ / Cu is greater than or equal to a preset value and when tanδ / Cu is less than a preset value.
7. A diagnostic method for evaluating the risk of abnormalities occurring within an oil-filled cable using insulating oil, A diagnostic method according to any one of claims 4 to 6, wherein the degree of risk of abnormality is diagnosed using only measurements taken within a predetermined period from the date of diagnosis to the number of years elapsed from the date the oil-filled cable was laid.