JP2023111322A - Method for diagnosing degree of risk of abnormality occurrence of oil-filled cable - Google Patents

Abstract

To provide a diagnostic method for highly accurately evaluating a degree of risk of abnormality occurrence of an oil-filled cable.SOLUTION: A diagnostic method includes: a step 1 of creating a trend graph; a step 2 of obtaining a maximum amount of copper dissolved in oil; and a step 3 of obtaining an amount of reduction from the maximum amount of copper dissolved in oil, and evaluates a degree of risk of abnormality occurrence from evaluation results of at least characteristic values (a) to (c) based on preset respective reference values in an oil-filled cable evaluated as in need of diagnosis. The diagnostic method has a step 1 of preparing a trend graph, and evaluates the degree of risk of the abnormality occurrence by evaluation results of evaluating at least characteristic values (f) to (i) based on respective preset reference values in the oil-filled cable evaluated as in need of diagnosis.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a method of diagnosing the degree of risk of an abnormality occurring in an oil-filled cable.

Oil-filled electrical equipment, such as oil-filled transformers, is used because the reaction between the copper parts of the oil-filled electrical equipment and the sulfur component in the insulating oil produces conductive copper sulfide (sulfidation corrosion), which causes insulation breakdown. It is known to cause catastrophic damage to electrical equipment. Estimated sulfur components in insulating oil include sulfur components contained in insulating oil, eluted sulfur components eluted from materials such as insulating paper, and added sulfur components such as antioxidants that are added to insulating oil later. Conceivable.

Oil-filled electrical equipment, such as large transformers, uses oil-impregnated paper as an insulator. If copper sulfide adheres to this oil-impregnated insulating paper, a short circuit will occur between the coils and the coil will be destroyed. It has been reported as an insulation breakdown case overseas. In addition, it has been thought that oil-filled cables, which use oil-impregnated paper as insulation, deteriorate very slowly, but in recent years, cases of dielectric breakdown in aging oil-filled cable lines have been confirmed.

The reaction mechanism involved in the formation of copper sulfide in oil-filled electrical equipment such as large transformers is related to the antioxidant dibenzyl disulfide (hereinafter sometimes abbreviated as "DBDS") added to the insulating oil. are considered in detail. That is, DBDS adsorbs to coil copper, then DBDS reacts with coil copper to form a DBDS-copper complex, and the DBDS-copper complex decomposes into benzyl radicals, benzylsulfenyl radicals, and copper sulfide. It is reported that this is because a reaction occurs (see Patent Documents 1 to 3).

In Patent Documents 1 and 2, insulating oil is collected from a transformer in operation, DBDS, its decomposition products, by-products, etc. are analyzed to predict the generation of copper sulfide, and abnormal occurrence of oil-filled electrical equipment is predicted. It discloses a method for diagnosing the risk of Further, Patent Document 3 discloses a method of measuring the concentration of dibenzyl sulfoxide in insulating oil when the insulating oil is in an air atmosphere, and estimating the amount of copper sulfide produced based on the concentration. there is

However, in the diagnostic methods of Patent Documents 1 to 3, it is essential that DBDS is added to the insulating oil. , there is a problem that the amount of copper sulfide produced in the insulating oil cannot be estimated from the amount of DBDS-copper complex produced in the insulating oil. In addition, conventional inspection techniques for oil-filled cables include measuring the dielectric loss tangent (tan δ) of the insulating oil, analyzing the gas in the insulating oil, and analyzing the combustible gas generated by partial discharge (local dielectric breakdown of the insulating oil). Generally, gas analysis in oil is performed using the amount of natural gas as an indicator of the degree of deterioration, and no method has been implemented for diagnosing the degree of danger from the state of formation of organocopper compounds and copper sulfide.

JP 2010-010439 A JP 2012-156232 A JP 2014-045212 A

The present invention has been made in view of the conventional problems described above. It is an object of the present invention to provide a diagnostic method for highly accurately evaluating the risk of occurrence of an abnormality in an oil-filled cable.

In order to solve the above problems, the present inventors have conducted extensive studies. As a result, from the dismantling investigation results of oil-filled cables using insulating oil, it was found that copper sulfide was generated even in the oil-filled cable; A correlation is observed between the amount of dissolved copper in oil and the dielectric loss tangent (tan δ) of the insulating oil; ) and the total amount of combustible gas (TCG) in the trend graph showing changes over time, each value tends to decrease after taking a maximum value; hydrogen is contained in the insulating oil when organocopper compounds and copper sulfide are generated Combustible gas is generated and the total combustible gas (TCG) in the insulating oil increases; when organic copper compounds and copper sulfide are generated, multiple unique characteristic values change; did.
Then, the amount of dissolved copper in oil, the dielectric loss tangent (tan δ) and the amount of combustible gas (TCG) of the insulating oil sampled from the oil-filled cable and the amount of hydrogen gas generated in the combustible gas are used to determine the production status of organocopper compounds and copper sulfide. can be estimated, and 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 abnormalities in oil-filled cables with high accuracy. The discovery led to the completion of the present invention.

A diagnostic method of the present invention is a diagnostic method for evaluating the risk of an abnormality occurring in an oil-filled cable using insulating oil,
Depending on the course of use of the oil-filled cable, insulating oil is sampled from the oil-filled cable, and the amount of dissolved copper in oil, the amount of hydrogen gas generated (H ₂ ), the dielectric loss tangent (tan δ), and the combustibility of the insulating oil are measured. Based on the measured value obtained by measuring the total gas amount (TCG), (A) a trend graph showing the change over time of the dielectric loss tangent (tan δ) and the total amount of combustible gas (TCG), or (B) dissolved copper in oil Step 1 of creating a trend graph showing changes over time in the amount and dielectric loss tangent (tan δ) and total combustible gas content (TCG);
Step 2 for determining the maximum amount of dissolved copper in oil based on the measured value obtained in step 1;
Step 3 of determining the amount of decrease from the maximum amount of dissolved copper in oil based on the measured value obtained in Step 1 and the maximum amount of dissolved copper in oil determined in Step 2;
has
Evaluate an oil-filled cable that has a trend transition in which the dielectric loss tangent (tan δ) shown in the trend graph created in step 1 is in a decreasing process or in a substantially steady state after decreasing as requiring diagnosis,
In the oil-filled cable evaluated as requiring diagnosis, at least the following characteristic values (a) to (c) are evaluated based on preset reference values, respectively, to evaluate the risk of occurrence of the abnormality. characterized by
(a) amount of decrease from the maximum amount of dissolved copper in oil;
(b) the total amount of combustible gas (TCG), and (c) the amount of hydrogen gas generated (H ₂ )

Further, the diagnostic method of the present invention is a diagnostic method for evaluating the risk of occurrence of an abnormality in an oil-filled cable using insulating oil, comprising:
Depending on the course of use of the oil-filled cable, insulating oil is sampled from the oil-filled cable, and the amount of dissolved copper in oil, the amount of hydrogen gas generated (H ₂ ), the dielectric loss tangent (tan δ), and the combustibility of the insulating oil are measured. Based on the measured value obtained by measuring the total gas amount (TCG), (A) a trend graph showing the change over time of the dielectric loss tangent (tan δ) and the total amount of combustible gas (TCG), or (B) dissolved copper in oil A step 1 of creating a trend graph showing changes over time in the amount and dielectric loss tangent (tan δ) and total combustible gas amount (TCG),
Evaluate an oil-filled cable that has a trend transition in which the dielectric loss tangent (tan δ) shown in the trend graph created in step 1 is in a decreasing process or in a substantially steady state after decreasing as requiring diagnosis,
In the oil-filled cable evaluated as requiring diagnosis, at least the following characteristic values (f) to (i) are evaluated based on preset reference values, respectively, to evaluate the risk of occurrence of the abnormality. characterized by
(f) the amount of dissolved copper in the insulating oil;
(g) the total combustible gas amount (TCG);
(h) the amount of hydrogen gas generated (H ₂ ), and (i) H ₂ /TCG

The diagnostic method of the present invention further has a step 6 of obtaining tan δ / Cu, which is the ratio of the dielectric loss tangent (tan δ) to the amount of dissolved copper in oil, based on the measured value obtained in step 1,
At least one of the reference values is set differently depending on whether the tan δ/Cu is a preset value or more and when the tan δ/Cu is less than a preset value. preferably.

In such a diagnostic method of the present invention, the conductor constituting the oil-filled cable reacts with hydrocarbons and non-hydrocarbon compounds in the insulating oil, dissolves in the insulating oil as a copper complex or a copper compound, and the copper complex Aggregates on the insulating paper of the reinforcing insulating layer in the high electric field region by dielectrophoresis, promotes the oxidation of the insulating oil as a copper catalyst and the bonding reaction with the copper complex or copper compound, generates an organic copper compound, and eventually sulfides. It is based on the presumption that copper is produced, and this organocopper compound or copper sulfide dielectrophoreses in the high electric field region and aggregates and deposits on the insulating paper. In addition, regarding the insulating oil before using the oil-filled cable, a linear positive correlation is observed between the dielectric loss tangent (tan δ) and the amount of dissolved copper in oil. It is based on the assumption that copper compounds and copper sulfide will be produced more.

Diagnosis method for evaluating the risk of abnormalities in oil-filled cables based on characteristic values (a) to (c) in oil-filled cables using insulating oil (hereinafter sometimes referred to as "detailed method" ), it is possible to evaluate the risk of abnormalities with high accuracy using all the data accumulated since the operation of the oil-filled cable. More specifically, in the detailed method, the characteristic values (a) decrease from the maximum dissolved copper amount in oil, (b) total combustible gas amount (TCG), and (c) hydrogen gas generation amount (H ₂ ) are evaluated comprehensively based on preset reference values, and the degree of risk of occurrence of an abnormality is evaluated based on the evaluation results.
The amount of dissolved copper in oil is an index representing the amount of copper that is a factor in the formation of organic copper compounds and copper sulfide, and thus is a factor related to the formation of organic copper compounds and copper sulfide. Also, the total combustible gas (TCG) amount is an index representing an increase in insulating oil dissolved gas.

In an oil-filled cable using insulating oil, a diagnostic method for evaluating the risk of abnormalities occurring in the oil-filled cable based on the characteristic values (f) to (i) (hereinafter sometimes referred to as "simple method" ), limited data from the data accumulated since the operation of the oil-filled cable (measurement values measured within a specified period from the date of diagnosis to the number of years elapsed from the date the oil-filled cable was installed) ), it is possible to evaluate the risk of anomaly occurrence with high accuracy. More specifically, in the simple method, the characteristic values are (f) the amount of dissolved copper in the insulating oil, (g) the total amount of combustible gas (TCG), (h) the amount of hydrogen gas generated (H ₂ ), and (i) H ₂ /TCG is comprehensively evaluated based on preset reference values, and the degree of risk of abnormal occurrence is evaluated based on the evaluation results.

According to the diagnostic method of the present invention, analysis of gas in oil (diagnosis of trend tendency of gas generated by partial discharge or thermal deterioration), diagnosis of deterioration tendency of electrical properties of insulating oil (tan δ, TCG, volume resistivity, measurement of AC withstand voltage ), water intrusion diagnosis (moisture content measurement), etc. Diagnosis is based on the mechanism of copper sulfide formation from a different perspective, so the oil-filled cable uses insulating oil that does not contain dibenzyl disulfide. It is also possible to diagnose the degree of risk of abnormal occurrence with high accuracy.

When using limited data from the data accumulated since the operation of the oil-filled cable, use the simple method, and when using the data accumulated since the operation of the oil-filled cable, use the detailed method. This makes it possible to evaluate the risk of anomaly occurrence with high accuracy. Therefore, for example, for an oil-filled cable that has been in operation for 30 to 40 years, it is possible to easily and accurately diagnose the degree of risk of occurrence of abnormality.

It is a figure which shows an example of the trend graph which shows the time-dependent change of tan-delta and TCG. FIG. 4 is a schematic diagram showing how to obtain TCG _Ave , which is the average value of TCG.

Hereinafter, a diagnostic method for evaluating the risk of occurrence of an abnormality in an oil-filled cable (hereinafter referred to as "OF cable") according to the present invention will be described in detail.

≪Deterioration of OF cable≫
With OF cables, simply using oil-impregnated insulating paper as an insulator does not satisfy the required characteristics because air bubbles are generated in the insulating oil due to a pressure drop in the insulating oil due to temperature changes. It is designed to withstand high electric field intensity by providing an oil passage and constantly applying pressure above atmospheric pressure to the insulating oil from an oil tank installed outside. The insulator of the OF cable is formed by winding tape-shaped insulating paper and impregnating it with insulating oil. At that time, in order to improve the bending characteristics, the insulating paper is usually not wrapped, and the gap is provided evenly.

Factors that reduce the insulation performance of OF cables are thought to include a decrease in the degree of polymerization of insulating paper due to overheating, damage, deformation, collapse of insulation due to vibration and thermal expansion, negative pressure, oil leakage, and abnormal insulating oil properties. . The electrical characteristics of the OF cable have a margin for AC voltage, but if there is a defect due to misalignment or damage to the insulating paper due to core misalignment, etc., partial discharge will occur at the defective part due to overvoltage, and gas will be generated. , and if it is repeated, it may exist as a void in the defect. Furthermore, since voids have extremely low dielectric strength, partial discharge may continue due to the application of AC voltage.

<<Copper sulfide generation mechanism in OF cable>>
In the conventional generation of copper sulfide in insulating oil to which DBDS is added, DBDS reacts with the copper of the conductor, the DBDS-copper complex diffuses into the insulating oil, and the DBDS-copper complex diffused in the oil becomes insulating paper. It is presumed to be due to the mechanism that copper sulfide is generated by being adsorbed on and decomposed by thermal energy.

On the other hand, in the present invention, copper sulfide in the OF cable is generated by (i) reacting the conductor with the insulating oil, (ii) dissolving in the insulating oil as a copper complex or copper compound, and (iii) dissolving the copper complex Alternatively, the copper compound aggregates in a high electric field region due to dielectrophoresis, (iv) promotes the oxidation of insulating oil as a copper catalyst and the bonding reaction with a copper complex or a copper compound to generate a polymeric organic copper compound, ( v) The produced organic copper compound further aggregates in the high electric field region by dielectrophoresis, and the copper complex, copper compound, or organic copper compound aggregated in the high electric field region reacts with the sulfur component contained in the insulating paper or insulating oil. It is presumed that this is due to the mechanism that copper sulfide is generated. In the present invention, the sulfur component that reacts with the copper complex, the copper compound, or the organic copper compound is not limited to the component added to the insulating oil like DBDS, but the sulfur compound used in the production of the insulating paper. It is assumed that the sulfur component derived from it and the sulfur component derived from petroleum, which is the raw material of the insulating oil, are also included.

Further, in the above mechanism, it is presumed that the copper complex or the copper compound reacts with the insulating oil to generate a polymeric organocopper compound. Such organocopper compounds are solid substances with large molecular weights, and are aggregated by dielectrophoresis in a high electric field region, depositing on cable cores, etc., and, like copper sulfide, cause deterioration of insulation performance and dielectric breakdown. is assumed.

That is, the copper sulfide generation mechanism according to the present invention is based on the assumption that organic copper compounds and copper sulfide are generated over time even in the case of insulating oil such as DBDS that does not contain a sulfur compound, although the reaction rate is very slow. Based on this, it is estimated that the three conditions of copper + insulating oil + high electric field are necessary for the production of organocopper compounds and copper sulfide.

≪Diagnostic method based on copper sulfide formation mechanism≫
According to the copper sulfide generation mechanism in the OF cable, (ii) when the copper complex or copper compound dissolves in the insulating oil, the amount of dissolved copper in the oil and the dielectric loss tangent (tan δ) of the insulating oil increase. After that, (iii) when the copper complex or copper compound aggregates in the high electric field region, the dissolution amount reaches the maximum value, and eventually, (iv) organic copper compound formation and (v) copper sulfide formation occur, dissolving in oil. The amount of copper and the dielectric loss tangent (tan δ) of the insulating oil are reduced.

On the other hand, the gas generated by the formation reaction of the copper complex, the organic copper compound, and the copper sulfide formation reaction is absorbed by the insulating oil, so the gas concentration in the oil increases, and the amount of hydrogen gas generated in the oil (H ₂ ) and total combustible gas (TCG) measurements increase.

FIG. 1 is an example of a trend graph showing changes over time in the dielectric loss tangent (tan δ) of the insulating oil and the total amount of combustible gas in the oil (TCG) based on the copper sulfide formation mechanism in the OF cable. .

Here, the trend graphs of the dielectric loss tangent (tan δ) and the total combustible gas amount (TCG) correlate with the trend graphs of the dissolved copper amount in oil and the total combustible gas amount (TCG). That is, from the trend graph (Fig. 1) of the dielectric loss tangent (tan δ) and the total amount of combustible gas (TCG), the "decrease" period of these characteristic values is the formation period of the organocopper compound and copper sulfide (in addition, in Fig. 1 is abbreviated as "copper sulfide formation period".), and if these characteristic values (absolute values) are large, the amount of dissolved copper in oil that becomes organic copper compounds and copper sulfide is large. , the production of organocopper compounds and copper sulfides can be estimated to increase. Therefore, (A) a trend graph showing changes over time in the dielectric loss tangent (tan δ) and the total combustible gas amount (TCG), or (B) the amount of dissolved copper in oil and the dielectric loss tangent (tan δ) and the total combustible gas amount (TCG) In the trend graph showing changes over time, it is possible to estimate the formation of organocopper compounds and copper sulfide in the OF cable from the maximum value of the dielectric loss tangent (tan δ).

It has been confirmed by preliminary tests that the approximation formula of the approximate straight line showing the relationship between the amount of dissolved copper in oil and the dielectric loss tangent can be represented by a linear formula. Based on these findings, the present inventors confirmed that the maximum amount of dissolved copper in oil can be estimated from the maximum value of the tan δ value using the following formula (1).
[Cu] _max = (tan δ _max - tan δ ₀ ) × {[Cu]/(tan δ - tan δ ₀ )} (1)
In the above formula (1), [Cu] _max is the maximum amount of dissolved copper in oil, tan δ _max is the maximum value derived from the trend graph of the dielectric loss tangent (tan δ), and tan δ ₀ is the new insulating oil. is the value of the dielectric loss tangent (tan δ), and tan δ and [Cu] are the values of the dielectric loss tangent (tan δ) and the amount of dissolved copper in the insulating oil extracted at a certain point from the actual equipment after the start of use, respectively. be.

According to the above formula (1), the dielectric loss tangent value (tan δ ₀ ) of new insulating oil, the past maximum dielectric loss tangent value (tan δ _max ) of insulating oil extracted from actual equipment, and a certain point (for example , the most recent measurement point) and the amount of dissolved copper in oil, _the maximum amount of dissolved copper in oil [Cu] It is possible to estimate the generation situation of
That is, it can be estimated that when the maximum amount of dissolved copper in oil is large, the amounts of dissolved copper in oil that become organic copper compounds and copper sulfide are large, so that the amounts of organic copper compounds and copper sulfide produced are large. . In addition, if the difference between the maximum amount of dissolved copper in oil and the amount of dissolved copper in oil at the time of the most recent measurement (decrease from the maximum amount of dissolved copper in oil) is large, at the time of that measurement, the organocopper compound and It can be estimated that a large amount of copper sulfide is produced.

<Diagnosis method>
The diagnostic method of the present invention is described in detail below. In the diagnostic method of the present invention for evaluating the risk of abnormality occurring in an oil-filled cable, as step 1 of the simple method and the detailed method, the insulating oil sampled from the oil-filled cable is evaluated for the amount of dissolved copper in the oil and the amount of hydrogen gas generated. (H ₂ ), dielectric loss tangent (tan δ), and total combustible gas amount (TCG) are measured, and based on each measurement, (A) change in dielectric loss tangent (tan δ) and total combustible gas amount (TCG) over time or (B) a trend graph showing temporal changes in the amount of dissolved copper in oil, the dielectric loss tangent (tan δ), and the total amount of combustible gas (TCG). Specific examples of combustible gases include hydrogen, carbon monoxide, methane, ethane, and acetylene.

When diagnosing the risk of anomaly occurrence using only the measured values measured within a predetermined period of time from the date of diagnosis to the date on which the oil-filled cable is laid, the simplified method described later is used to diagnose the occurrence of an anomaly. perform a diagnosis of the degree of risk of When diagnosing the risk of anomalies by including not only the measured values measured within a predetermined period from the diagnosis date but also the measured values measured before the predetermined period from the diagnosis date, the detailed method described later is used. Diagnose the risk of abnormal occurrence by Thereby, a suitable diagnostic method can be selected according to the holding status of the accumulated data. Note that the "predetermined period" can be appropriately set according to the number of years that have passed since the day the oil-filled cable was installed. An example of the “predetermined period” is (the number of years elapsed from the date the oil-filled cable was installed)×0.25. The simplified method and the detailed method are described in detail below.

(1) Simplified method In the simplified method, equipment hazards are diagnosed from the formation of organocopper compounds and copper sulfide. That is, each characteristic value of (f) the amount of dissolved copper in the insulating oil, (g) the total amount of combustible gas (TCG), (h) the amount of hydrogen gas generated (H ₂ ), and (i) H ₂ /TCG is comprehensively evaluated based on a preset reference value, and the degree of risk of occurrence of an abnormality in the equipment is diagnosed based on the evaluation results based on specific diagnostic criteria. Note that (f) the reference value for the amount of dissolved copper in the insulating oil may be set one, or two or more.

In the simple method, step 4 of obtaining the average value TCG _Ave of the total combustible gas (TCG) in the generation period of the organic copper compound and copper sulfide shown in the trend graph, and the production of the organic copper compound and copper sulfide shown in the trend graph. and Step 5 of obtaining the average value H _2Ave of the hydrogen gas generation amount (H ₂ ) in the generation period, and the (g) total combustible gas amount (TCG) is the average value TCG _Ave of the total combustible gas amount (TCG) Preferably, the (h) hydrogen gas generation amount (H ₂ ) is an average value H _2Ave of the hydrogen gas generation amount (H ₂ ), and the (i) H ₂ /TCG is H _2Ave /TCG _Ave. . Thus, (g) using the average value TCG _Ave of the total combustible gas amount (TCG) as the total combustible gas amount (TCG), and (h) the hydrogen gas generation amount (H ₂ ) as the hydrogen gas generation amount (H ₂ ) By using the average value H _2Ave and (i) using H _2Ave /TCG _Ave as H ₂ /TCG, the numerical value is close to the actual characteristics of change over time, and the diagnostic accuracy of the risk of abnormality occurrence can be improved. .

FIG. 2 is a diagram showing how to determine the average value TCG _Ave of the total amount of combustible gas (TCG), and the average value TCG _Ave is determined according to the concept of interval integration. For example, as shown in FIG. 2, when the total combustible gas (TCG) is measured at four points of time A (the year the oil-filled cable was installed), B, C and D, the intermediate time between A and B ( 2.5 years after 2010), midway between B and C (1.5 years after 2015), and midway between C and D (1.0 years after 2018) Separate each section with . Then, the total combustible gas amount (TCG) of A is the period from A to the middle of A and B (2.5 years), and the total combustible gas amount (TCG) of B is the middle of A and B Assume that the period from time to the middle of B and C (2.5 years + 1.5 years = 4.0 years), the total combustible gas amount (TCG) of C is from the middle of B and C to C and D (1.5 years + 1.0 years = 2.5 years), and the total combustible gas amount (TCG) of D is the period from the middle of C and D to D (1.0 years). Then, TCG _Ave is obtained by dividing the total area of each section set as described above by the number of years from A to D. For example, in FIG. 2, TCG _Ave can be calculated by the following formula (2).
TCG _Ave (ppm)
= {A (50 ppm x 2.5 years) + B (100 ppm x 4.0 years) + C (250 ppm x 2.5 years) + D (200 ppm x 1.0 years)} / 10.0 years = 135 ppm (2)

To generalize the method _{for obtaining} the above TCG _Ave , let _the measurement years be N ₁ , N ₂ , . When the measured values of TCG at the N _{1 ,} N ₂ , . . . N _m are TCG ₁ , TCG ₂ , _. can be calculated.

The average value H _2Ave of the amount of hydrogen gas generated (H ₂ ) is also obtained according to the concept of interval integration, similarly to TCG _Ave. To generalize the _method of obtaining _H2Ave , let _the measurement years be _N1 , _{N2 ,} . year), and _the measured values of _H2 at the N _{1 , N 2 , .} It can be calculated by the following formula (4).

In the simplified method, the characteristic values (f) to (i) and the characteristic value (j), the number of years elapsed since the installation of the oil-filled cable, were evaluated based on the preset reference values. It is preferable to assess the risk of occurrence. In this way, by diagnosing the risk of abnormality occurrence using the characteristic values (f) to (j), the numerical values are close to the actual characteristics of changes over time, and the diagnostic accuracy of the risk of abnormality occurrence can be improved. can be done.

The simplified method further includes a step 6 for obtaining tan δ / Cu, which is the ratio of the dielectric loss tangent (tan δ) to the amount of copper dissolved in oil, and when tan δ / Cu is a preset value or more. , tan δ/Cu is less than a preset value, preferably at least one reference value is set differently. At this time, when tan δ / Cu is a preset value or more and when tan δ / Cu is less than a preset value, all of the above (f) to (j) may be different, or part of the above (f) to (j) may be different. Preliminary investigations have shown that the reference values of the characteristic values (f) to (j) may change depending on whether tan δ / Cu is a specific set value or more and when it is less than a specific set value. . The reason for this is that when tan δ/Cu is greater than the set value, organic copper compounds and copper sulfide have already been generated in many places in the equipment at that time, but after that, deterioration positions of the equipment and the characteristics of the insulating oil As a result of comparing the values, it was found that tan δ/Cu was larger than the set value when deterioration occurred from the outside to the inside of the facility. When the degree of deterioration is the same and the deterioration position is outside the equipment and when the deterioration position is from the outside to the inside, it was confirmed that the TCG and the amount of decrease tend to be low when the deterioration is from the outside to the inside. As a result, it is considered that the reference values of the characteristic values (f) to (j) change. Therefore, by setting at least one reference value among the characteristic values (f) to (j) to be different depending on whether tan δ/Cu is equal to or greater than the set value and when it is less than the set value, the It is possible to diagnose the risk of abnormality occurrence with high accuracy.

Table 1 below shows an example in which different reference values are set for tan δ/Cu of 0.9 or more and less than 0.9. In Table 1 below, two reference values are set for (f) the amount of dissolved copper in insulating oil, and (g) the total combustible gas amount (TCG) is the average value of the total combustible gas amount (TCG) TCG _Ave (h) the average value H _2Ave of the hydrogen gas generation rate (H ₂ ) was used as the hydrogen gas generation rate (H ₂ ), and (i) H _2Ave /TCG _Ave was used as H ₂ /TCG.

本発明の一例では、特性値（ｆ）～（ｊ）について、上記表１に記載の基準値以上であるか、または、基準値未満であるか、を確認し、各特性値の確認結果を下記表２に従って総合的に評価して異常発生の危険度を診断する。なお、上記表１に記載の基準値は一例であり、油入りケーブルのタイプ・使用環境等に応じて適宜、好適な基準値を設定することができる。 (Reference values for characteristic values (f) to (i))

In one example of the present invention, it is confirmed whether the characteristic values (f) to (j) are equal to or greater than the reference values shown in Table 1 above or less than the reference values, and the confirmation results of each characteristic value are obtained. Comprehensively evaluate according to Table 2 below to diagnose the degree of risk of abnormal occurrence. Note that the reference values shown in Table 1 are only examples, and appropriate reference values can be set according to the type of oil-filled cable, usage environment, and the like.

(Diagnostic Criteria for Abnormal Occurrence Risk)
Of the ranks A to D diagnosed according to the criteria shown in Table 2 below, rank A has a “high” risk of anomaly occurrence, rank B has a “medium” risk of anomaly occurrence, and rank C has a risk of anomaly occurrence. The degree is "small", and rank D is diagnosed as "extremely low" in the risk of abnormality occurrence.

(Diagnostic Criteria for Abnormal Occurrence Risk)
By evaluating and ranking the degree of danger in the above order, it is possible to judge the degree of danger of equipment relatively easily, and the results are consistent with the dismantling investigation results of oil-filled cables using insulating oil. . Note that the applicable items described in Table 2 above are only examples, and suitable applicable items can be appropriately set according to the type of the oil-filled cable, the usage environment, and the like.

(2) Detailed method In the detailed method, as in the above (1) simplified method, (a) decrease from the maximum amount of copper dissolved in oil, (b) total combustible gas (TCG), and (c) hydrogen gas generation Amount (H ₂ ) is comprehensively evaluated based on a preset reference value, and the risk of occurrence of an abnormality in the equipment is diagnosed based on the evaluation result based on specific diagnostic criteria.

In the detailed method, further, step 4 for obtaining the average value TCG _Ave of the total combustible gas amount (TCG) in the generation period of the organic copper compound and copper sulfide shown in the trend graph, and the organic copper compound and copper sulfide shown in the trend graph. (b) the total combustible gas amount ( _TCG ) is the average value _{TCG Ave} of the total combustible gas amount (TCG); , (c) The hydrogen gas generation amount (H ₂ ) is preferably the average value H _2Ave of the hydrogen gas generation amount (H ₂ ). In this way, (b) the average value TCG _Ave of the total combustible gas amount (TCG) is used as the total combustible gas amount (TCG), and (c) the hydrogen gas generation amount (H ₂ ) is the hydrogen gas generation amount (H ₂ ) By using the average value H _2Ave of , it becomes a numerical value close to the actual characteristic of change over time, and the diagnostic accuracy of the degree of risk of abnormality occurrence can be improved.

In the detailed method, in step 2, based on the measured value obtained in step 1, it is preferable to obtain the maximum dissolved copper amount in oil by the following formula (1). However, in the following formula (1), [Cu] _max is the maximum amount of dissolved copper in oil, tan δ _max is the maximum value of the dielectric loss tangent (tan δ) derived from the trend graph created in step 1, tan δ ₀ is the value of the dielectric loss tangent (tan δ) of insulating oil (new insulating oil) before the start of use of the oil-filled cable, and tan δ and [Cu] are each at a certain point after the start of use of the oil-filled cable. These are values of the dielectric loss tangent (tan δ) of the insulating oil and the amount of dissolved copper in the oil. The point in time after the start of use of the oil-filled cable is preferably the most recent (at the time of diagnosis) measurement point, but any point in the past during the generation period of organocopper compounds and copper sulfide There may be.
[Cu] _max = (tan δ _max - tan δ ₀ ) × {[Cu]/(tan δ - tan δ ₀ )} (1)
When the maximum amount of dissolved copper in oil [Cu] _max is large, the amount of dissolved copper in oil that becomes organic copper compounds and copper sulfide is large, so it can be estimated that the amounts of organic copper compounds and copper sulfide produced are large. .

Next, in step 3 of the detailed method, dissolved copper in the insulating oil at a certain point after the generation period of organic copper compounds and copper sulfide derived from the trend graph of total combustible gas (TCG) created in step 1 The decrease from the maximum dissolved copper amount in oil is calculated as the difference ([Cu] _max - [Cu]) between the amount ([Cu]) and the maximum dissolved copper amount ([Cu] _max ). The point in time after the period of generation of the organocopper compound and copper sulfide is the most recent point in time of measurement (at the time of diagnosis) (the same shall apply hereinafter). If the amount of dissolved copper in oil at a certain point after the generation period of organic copper compounds and copper sulfide is significantly reduced from the maximum amount of dissolved copper in oil It can be estimated that a large amount of copper compounds and copper sulfide are produced.

In the detailed method, in the oil-filled cable evaluated as requiring diagnosis, the characteristic values (a) to (c), the characteristic value (d) the amount of dissolved copper in the insulating oil and the characteristic value (e) created in step 1 Evaluate at least one of the characteristic values of the elapsed years from the time when the dielectric loss tangent (tan δ) starts to decrease to the time when the decrease ends, as shown in the trend graph, based on preset reference values. It is preferable to evaluate the degree of risk of anomaly occurrence based on the result of the inspection. In this way, by diagnosing the risk of anomaly occurrence using the characteristic values (a) to (e), the numerical values are close to the actual characteristics of changes over time, and the diagnostic accuracy of the risk of anomaly occurrence can be improved. can be done.

In addition, the detailed method further includes a step 6 for obtaining tan δ / Cu, which is the ratio of the dielectric loss tangent (tan δ) to the amount of copper dissolved in oil, and when tan δ / Cu is a preset value or more. , tan δ/Cu is less than a preset value, preferably at least one reference value is set differently. At this time, when tan δ / Cu is a preset value or more and when tan δ / Cu is less than a preset value, all of the above (a) to (e) may be different, and some of the above (a) to (e) may be different. Preliminary investigations have shown that the reference values for the characteristic values (a) to (e) may change depending on whether tan δ / Cu is a specific set value or more and when it is less than a specific set value. . The reason for this is that when tan δ/Cu is greater than the set value, organic copper compounds and copper sulfide have already been generated in many places in the equipment at that time, but after that, deterioration positions of the equipment and the characteristics of the insulating oil As a result of comparing the values, it was found that tan δ/Cu was larger than the set value when deterioration occurred inside the facility. When the degree of deterioration is the same and the deterioration position is outside the facility and when the deterioration position is from the outside to the inside, it was confirmed that the TCG and the amount of decrease tend to be low when the deterioration is from the outside to the inside. As a result, it is considered that the reference values of the characteristic values (a) to (e) change. Therefore, by setting at least one reference value among the characteristic values (a) to (e) differently depending on whether tan δ/Cu is equal to or greater than the set value or less than the set value, the It is possible to diagnose the risk of abnormality occurrence with high accuracy.

本発明の一例では、特性値（ａ）～（ｅ）について、上記表３に記載の基準値以上であるか、または、基準値未満であるか、を確認し、各特性値の確認結果を下記表４に従って総合的に評価して異常発生の危険度を診断する。なお、上記表３に記載の基準値は一例であり、油入りケーブルのタイプ・使用環境等に応じて適宜、好適な基準値を設定することができる。 Table 3 below shows an example in which different reference values are set for tan δ/Cu of 0.9 or more and less than 0.9. In Table 3 below, (b) the total amount of combustible gas (TCG) is the average value TCG _Ave of the total amount of combustible gas (TCG), and (c) the amount of hydrogen gas generated (H ₂ ) is the amount of hydrogen gas generated ( H ₂ ), the average value H _2Ave was used.
(Reference values for characteristic values (a) to (e))

In one example of the present invention, it is confirmed whether the characteristic values (a) to (e) are equal to or greater than the reference values shown in Table 3 above, or are less than the reference values, and the confirmation results of each characteristic value are obtained. Comprehensively evaluate according to Table 4 below to diagnose the degree of risk of abnormal occurrence. Note that the reference values shown in Table 3 are only examples, and appropriate reference values can be set according to the type of oil-filled cable, usage environment, and the like.

（異常発生の危険度の診断基準）
上記の順で危険度を評価しランク付けすることにより、設備の危険度を比較的簡易に判断することができ、また絶縁油を使用した油入りケーブルの解体調査結果とも一致した結果が得られる。なお、上記表４に記載の該当項目は一例であり、油入りケーブルのタイプ・使用環境等に応じて適宜、好適な該当項目を設定することができる。 Of the ranks A to D diagnosed according to the criteria shown in Table 4 below, rank A has a "high" risk of abnormality occurrence, rank B has a "medium" risk of abnormality occurrence, and rank C has a risk of abnormality occurrence. The degree is "small", and rank D is diagnosed as "extremely low" in the risk of abnormality occurrence.

(Diagnostic Criteria for Abnormal Occurrence Risk)
By evaluating and ranking the degree of danger in the above order, it is possible to judge the degree of danger of equipment relatively easily, and the results are consistent with the dismantling investigation results of oil-filled cables using insulating oil. . Note that the applicable items described in Table 4 above are only examples, and suitable applicable items can be appropriately set according to the type of the oil-filled cable, the usage environment, and the like.

Next, the confirmation results of the effects of the diagnostic method according to the present invention will be specifically described, but the present invention is not limited only to the following examples.

(1) Confirmation of effects by this diagnostic method For actual equipment (120 OF cables), estimated diagnostic results diagnosed based on the diagnostic methods (simplified method and detailed method) of the present invention were compared with results of dismantling investigation. Table 5 shows the results. The presumed diagnosis based on the diagnostic method of the present invention and the dismantling investigation were performed by the following methods, respectively.

<Estimated diagnosis based on the diagnostic method of the present invention>
First, for the sample oil collected from each actual facility, the amount of dissolved copper in the insulating oil, the amount of hydrogen gas generated (H ₂ ), the dielectric loss tangent (tan δ), and the total amount of combustible gas (TCG) were measured by the following measurement methods. Based on the measured values obtained, a trend graph showing changes over time in the dielectric loss tangent (tan δ) and the total combustible gas amount (TCG) was created (step 1 of simple method or detailed method).

Furthermore, in the actual facility (120 OF cables), the risk of abnormal occurrence was measured using only the measured value measured in a predetermined period (elapsed years x 0.25 years) for the number of years elapsed from the installation date of the cable. The 64 OF cables for which the degree is to be diagnosed are subject to the simplified method, and if there are measured values that exceed a predetermined period for the number of years since the cable was installed, all measured values are used. Diagnose the risk of abnormal occurrence by detailed method. The 56 OF cables were subject to diagnosis by the detailed method.

Next, for the 64 OF cables to be diagnosed by the simplified method, from the total combustible gas amount (TCG) and the hydrogen gas generation amount (H ₂ ) measured in the above step 1, (g) the total combustible gas amount (TCG) , and (h) the average value H _2Ave of the amount of hydrogen gas generated (H ₂ ) was calculated (steps 4 and 5 of _the simplified method) to obtain (i) H _2Ave /TCG _Ave. After that, the characteristic values obtained for each actual facility are (f) the amount of dissolved copper in the insulating oil, (g) the average value of the total amount of combustible gas (TCG) TCG _Ave , (h) the amount of hydrogen gas generated ( H ₂ ) average value H _2Ave , (i) H _2Ave /TCG _Ave , and (j) elapsed years from the date of installation of the oil-filled cable are equal to or greater than the reference values preset in Table 1 above, or less than the reference value, and based on the results of this confirmation, the degree of risk of occurrence of an abnormality in the facility was diagnosed based on the diagnostic criteria in Table 2 above.

In addition, for the 56 OF cables to be diagnosed by the detailed method, the total amount of combustible gas (TCG), the amount of hydrogen gas generated (H ₂ ), the dielectric loss tangent (tan δ) and the dissolution of insulating oil in oil measured in the above step 1 From the amount of copper, calculate the average value TCG _Ave of the total amount of combustible gas (TCG), the average value H _2Ave of the amount of hydrogen gas generated (H ₂ ), and the maximum amount of dissolved copper in oil based on the above formula (1) ( Steps 2, 4 and 5 of the detailed method), and from the maximum amount of dissolved copper in oil determined in step 2, the amount of decrease from the maximum amount of dissolved copper in oil was calculated (step 3 of the detailed method). After that, the characteristic values obtained for each actual facility are (a) the amount of decrease from the maximum amount of dissolved copper in oil, (d) the amount of dissolved copper in insulating oil, and (b) the total amount of combustible gas (TCG). Average value of TCG _Ave , (e) When the dielectric loss tangent (tan δ) shown in the trend graph created in step 1 started to decrease (when the dielectric loss tangent (tan δ) showed a maximum value), the decrease ended Confirm whether the elapsed years up to the time and (c) the average value H _2Ave of the hydrogen gas generation amount (H ₂ ) are equal to or more than the reference value preset in Table 3 above or less than the reference value. Then, based on the results of this confirmation, the degree of risk of abnormalities occurring in the facility was diagnosed based on the diagnostic criteria in Table 4 above.

(Measurement condition)
The various measurements described above were carried out according to the following procedures.
Measurement of Dielectric Loss Tangent (tan δ) 50 ml of sample oil sampled from each actual equipment was placed in a liquid electrode, heated to 80° C., 1000 V was applied, and tan δ was measured with a tan δ measuring instrument.

・Measurement of amount of hydrogen gas generated (H ₂ ) and total amount of combustible gas (TCG) Gases (oxygen, nitrogen, hydrogen, methane, ethane, ethylene, acetylene, sulfur hexafluoride, carbon monoxide and carbon dioxide) were separated, extracted and analyzed. Total combustible gas (TCG) is the total amount of hydrogen, methane, ethane, ethylene, acetylene, and carbon monoxide analyzed.

・Measurement of the amount of dissolved copper in the insulating oil The sample oil sampled from each actual facility is diluted 10 times with xylene to prepare an adjusted solution, and the solution is analyzed by an inductively coupled plasma (ICP) emission spectrometer. The amount of copper dissolved in oil (mg) was analyzed. The calibration curve standard solution was prepared by diluting a commercially available oil-based copper-containing standard solution with blank oil and xylene in order to prepare a standard solution.

<Dismantling survey>
In the dismantling investigation, we examined the surface and inside of the reinforcing insulating paper of the actual equipment, and the innermost and outermost layers and inner layers of the cable insulating paper. It was carried out by visual confirmation, and evaluated as A to D based on the following diagnostic criteria.
In addition, to confirm the formation of organic copper compounds and copper sulfide, an electron microscope and a fluorescent X-ray analyzer were used to identify locations where both copper (Cu) and sulfur (S) were detected in the blackened areas on the insulating paper. At that specific location, the organocopper compound was confirmed by detecting absorption peaks of insulating oil, oxidation products, and sulfur compounds from the infrared absorption spectrum using a Fourier transform infrared spectrophotometer (FTIR), and copper sulfide This was confirmed by the detection of the Raman spectrum of copper sulfide by a microscopic Raman spectrometer.

<Diagnostic criteria>
A: Reinforcing insulating paper or cable insulating paper having black portions exceeding discharge traces, dots, or streaks is continuously laminated in the thickness direction, and the lamination state is dangerous in terms of insulation performance.
B: Reinforcing insulating paper or cable insulating paper having black portions exceeding discharge traces, dots, or streaks is continuously laminated in the thickness direction, and is in a laminated state in which insulation performance is affected.
C: Reinforcing insulating paper or cable insulating paper with discoloration in the form of dots or streaks is present only in the vicinity of the outermost layer, and the effect on insulation performance is small.
D: No black part.

Table 5 below shows a comparison between the diagnostic results obtained by the diagnostic method of the present invention and the survey results obtained by the dismantling survey.

As shown in Table 5, for the cables (64 wires) evaluated by the simple method, the diagnosis results based on the diagnosis method of the present invention were underestimated and overestimated with respect to the dismantling investigation results of the actual equipment. There were 5 facilities and 11 facilities, respectively, but for the others, the dismantling investigation results and the diagnostic results of the present invention were in agreement, and the matching rate was as high as 75.0%. In the cable (56 wires) evaluated by the detailed method, the diagnosis results based on the diagnosis method of the present invention were underestimated and overestimated with respect to the dismantling investigation results of the actual equipment. There were 4 facilities and 2 facilities, but the results of the dismantling survey and the diagnostic results of the present invention were consistent with the others, and the matching rate was very high at 89.3%. In addition, when looking at the whole (120 lines) of the simple method and the detailed method, the results of the dismantling investigation and the diagnostic results of the present invention were consistent with 98 facilities, and the matching rate was very high at 81.7%. From these results, it was confirmed that according to the diagnostic method of the present invention, results corresponding to the dismantling investigation results of actual equipment can be obtained. In addition, according to the diagnostic method of the present invention, it is not necessary to dismantle and test the actual equipment as in the dismantling investigation, and each measurement and evaluation can be performed only by sampling the test oil from the OF cable. It was confirmed that the degree of risk of actual equipment can be easily diagnosed.

Claims (10)

A diagnostic method for evaluating the risk of an abnormality occurring in an oil-filled cable using insulating oil, comprising:
Depending on the course of use of the oil-filled cable, insulating oil is sampled from the oil-filled cable, and the amount of dissolved copper in oil, the amount of hydrogen gas generated (H ₂ ), the dielectric loss tangent (tan δ), and the combustibility of the insulating oil are measured. Based on the measured value obtained by measuring the total gas amount (TCG), (A) a trend graph showing the change over time of the dielectric loss tangent (tan δ) and the total amount of combustible gas (TCG), or (B) dissolved copper in oil Step 1 of creating a trend graph showing changes over time in the amount and dielectric loss tangent (tan δ) and total combustible gas content (TCG);
Step 2 for determining the maximum amount of dissolved copper in oil based on the measured value obtained in step 1;
Step 3 of determining the amount of decrease from the maximum amount of dissolved copper in oil based on the measured value obtained in Step 1 and the maximum amount of dissolved copper in oil determined in Step 2;
has
Evaluate an oil-filled cable that has a trend transition in which the dielectric loss tangent (tan δ) shown in the trend graph created in step 1 is in a decreasing process or in a substantially steady state after decreasing as requiring diagnosis,
In the oil-filled cable evaluated as requiring diagnosis, at least the following characteristic values (a) to (c) are evaluated based on preset reference values, respectively, to evaluate the risk of occurrence of the abnormality. A diagnostic method characterized by:
(a) amount of decrease from the maximum amount of dissolved copper in oil;
(b) the total amount of combustible gas (TCG), and (c) the amount of hydrogen gas generated (H ₂ ) moreover,
Step 4 of obtaining the average value TCG _Ave of the total combustible gas amount (TCG) in the generation period of the organocopper compound and copper sulfide shown in the trend graph;
Step 5 of obtaining an average value H _2Ave of the hydrogen gas generation amount (H ₂ ) during the generation period of the organocopper compound and copper sulfide shown in the trend graph;
has
The (b) total combustible gas amount (TCG) is the average value TCG _Ave of the total combustible gas amount (TCG),
The diagnostic method according to claim 1, wherein the (c) hydrogen gas generation amount ( _H2 ) is an average value _H2Ave of the hydrogen gas generation amount ( _H2 ). In the step 2,
3. The diagnostic method according to claim 1 or 2, wherein the maximum dissolved copper amount in oil is obtained from the following formula (1).
[Cu] _max = (tan δ _max - tan δ ₀ ) × {[Cu]/(tan δ - tan δ ₀ )} (1)
(However, in the above formula (1), [Cu] _max is the maximum amount of dissolved copper in oil, and tan δ _max is the maximum value derived from the trend graph of the dielectric loss tangent (tan δ) created in Step 1 above. where tan δ ₀ is the value of the dielectric loss tangent (tan δ) of insulating oil (new insulating oil) before the start of use of the oil-filled cable, and tan δ and [Cu] are the values after the start of use of the oil-filled cable. These are the values of the dielectric loss tangent (tan δ) of the insulating oil and the amount of copper dissolved in the oil at the time.) In the oil-filled cable evaluated as requiring diagnosis, the characteristic values (a) to (c) and at least one of the following characteristic values (d) and (e) are set in advance. 4. The diagnostic method according to any one of claims 1 to 3, wherein the degree of risk of occurrence of the abnormality is evaluated based on the result of evaluation based on the reference value obtained.
(d) the amount of dissolved copper in the insulating oil;
(e) Elapsed years from the time when the dielectric loss tangent (tan δ) shown in the trend graph created in step 1 starts to decrease until the time when the decrease ends Furthermore, based on the measured value obtained in the step 1, a step 6 for obtaining a ratio of the dielectric loss tangent (tan δ) to the amount of copper dissolved in oil, tan δ / Cu,
At least one of the reference values is set differently depending on whether the tan δ/Cu is a preset value or more and when the tan δ/Cu is less than a preset value. 5. The diagnostic method according to any one of claims 1 to 4, characterized in that: A diagnostic method for evaluating the risk of an abnormality occurring in an oil-filled cable using insulating oil, comprising:
Depending on the course of use of the oil-filled cable, insulating oil is sampled from the oil-filled cable, and the amount of dissolved copper in oil, the amount of hydrogen gas generated (H ₂ ), the dielectric loss tangent (tan δ), and the combustibility of the insulating oil are measured. Based on the measured value obtained by measuring the total gas amount (TCG), (A) a trend graph showing the change over time of the dielectric loss tangent (tan δ) and the total amount of combustible gas (TCG), or (B) dissolved copper in oil A step 1 of creating a trend graph showing changes over time in the amount and dielectric loss tangent (tan δ) and total combustible gas amount (TCG),
Evaluate an oil-filled cable that has a trend transition in which the dielectric loss tangent (tan δ) shown in the trend graph created in step 1 is in a decreasing process or in a substantially steady state after decreasing as requiring diagnosis,
In the oil-filled cable evaluated as requiring diagnosis, at least the following characteristic values (f) to (i) are evaluated based on preset reference values, respectively, to evaluate the risk of occurrence of the abnormality. A diagnostic method characterized by:
(f) the amount of dissolved copper in the insulating oil;
(g) the total combustible gas amount (TCG);
(h) the amount of hydrogen gas generated (H ₂ ), and (i) H ₂ /TCG moreover,
Step 4 of obtaining the average value TCG _Ave of the total combustible gas amount (TCG) in the generation period of the organocopper compound and copper sulfide shown in the trend graph;
Step 5 of obtaining an average value H _2Ave of the hydrogen gas generation amount (H ₂ ) during the generation period of the organocopper compound and copper sulfide shown in the trend graph;
has
The (g) total combustible gas amount (TCG) is the average value TCG _Ave of the total combustible gas amount (TCG),
The (h) hydrogen gas generation amount (H ₂ ) is an average value H _2Ave of the hydrogen gas generation amount (H ₂ ),
7. The diagnostic method according to claim 6, wherein (i) _H2 /TCG is _H2Ave /TCG _Ave. The risk of occurrence of an abnormality is determined by evaluating the characteristic values (f) to (i) and the characteristic value (j), the number of years elapsed since the installation of the oil-filled cable, based on preset reference values. 8. The diagnostic method according to claim 6 or 7, characterized in that it evaluates Furthermore, based on the measured value obtained in the step 1, a step 6 for obtaining a ratio of the dielectric loss tangent (tan δ) to the amount of copper dissolved in oil, tan δ / Cu,
At least one of the reference values is set differently depending on whether the tan δ/Cu is a preset value or more and when the tan δ/Cu is less than a preset value. 9. The diagnostic method according to any one of claims 6 to 8, characterized in that: A diagnostic method for evaluating the risk of an abnormality occurring in an oil-filled cable using insulating oil, comprising:
Any one of claims 6 to 9, wherein the degree of risk of occurrence of an abnormality is diagnosed using only measured values measured within a predetermined period of time from the diagnosis date to the date on which the oil-filled cable is laid. The diagnostic method described in the paragraph.

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