JP4494815B2 - Fluid charging diagnostic method and fluid charging suppression method for oil-filled electrical equipment - Google Patents

Description

  The present invention relates to a method for diagnosing and suppressing a fluid charging phenomenon that occurs when insulating oil filled in an oil-filled electrical device flows.

  Oil-filled electrical equipment such as oil-filled transformers and oil-filled reactors have a structure in which an iron core and windings are housed in a tank, and the surface of the winding is insulated with a solid insulator such as insulating paper. The inside is filled with insulating oil for the purpose of ensuring the dielectric strength and cooling the winding and iron core, and forcibly circulates the insulating oil between the iron core and winding that are the heat source inside the tank and the cooler. Cooling, and the temperature of each part is kept within a specified range.

In an oil-filled electrical device having such a configuration, when the insulating oil flows on the surface of the winding, a flow charging phenomenon occurs at the interface between the solid insulator and the insulating oil, and a negative charge is generated on the surface of the solid insulator. When the potential increases and the potential of the portion increases and the potential exceeds the limit, a partial discharge is generated, which triggers an AC breakdown inside the device.
For this reason, the oil-filled electrical device has a configuration in which the flow charging phenomenon is suppressed by setting the flow rate of the insulating oil circulating inside to be low so that the flow charging phenomenon does not occur. The fluid charging phenomenon of the oil-filled electrical device is described in detail in Non-Patent Document 1, for example.

Regarding the flow charging phenomenon of oil-filled electrical equipment, various investigation results are shown in Part III [Maintenance management for flow charging] of Non-Patent Document 1.
The flow charging phenomenon is composed of three basic processes of charge transfer, charge separation, and charge relaxation, as shown in the conceptual diagram of the flow charging mechanism in Fig. 2-1-1 on page 71 of Non-Patent Document 1. ing.
In the charge transfer process, when insulating oil (liquid) and insulating paper (solid insulator) are in contact, one of positive and negative ions (negative ion) is selectively adsorbed on the insulating paper, and the other ion ( Positive ions) are distributed in the insulating oil in the vicinity thereof to form an electric double layer. In the charge distribution process, when the insulating oil flows in a state of charge transfer, the positive ions distributed in the insulating oil near the insulating paper are separated from the negative ions and carried away with the insulating oil. Positive and negative ions become unbalanced. In the charge relaxation process, the negative ions adsorbed on the insulating paper and the positive ions that have flowed away are released from each other, relaxed in the current path or in the insulating oil, and the charged ions gradually neutralize and disappear electrically. .

  In the oil-filled electrical equipment, the charging phenomenon between the insulating paper and the insulating oil is caused by the surface of the insulating paper (cellulose) as shown in FIG. 2-1-2 on page 71 of Non-Patent Document 1. There are polar groups such as hydroxyl groups (—OH) and carboxyl groups (—COOH), and oxygen in them has a high electronegativity and attracts electrons of hydrogen, so that the hydrogen on the surface is positively polarized and negative in oil. By selectively adsorbing ions, the insulating paper is negatively charged and the insulating oil is positively charged.

The charge due to the flow charging phenomenon that occurs in the oil-filled electrical equipment is related to the likelihood of the above three basic processes, and all of the three basic processes are included in the flow charge in the oil-filled electrical equipment. A neutral point winding leakage current (hereinafter referred to as winding leakage current) can be cited as a measure representing the magnitude of the characteristics. That is, since the winding leakage current is related to the occurrence limit of electrostatic discharge, it is used as a reference value for judging the risk of electrostatic discharge in the oil-filled electrical device. FIG. 2-2-5 on page 73 of Non-Patent Document 1 shows the temperature characteristics of the electrostatic discharge generation lower limit flow rate. The flow rate in this figure shows the lower limit flow rate at which discharge occurs as 1 pu, and the lower limit flow rate at which discharge occurs and the winding leakage current are temperature dependent.
This indicates that it is possible to predict the discharge phenomenon in the oil-filled electrical equipment due to the flow electrification phenomenon by measuring the winding leakage current. Since it cannot measure due to current, it is necessary to stop and measure the equipment.

  In an actual oil-filled electrical device, since it is difficult to stop, measuring the charging degree of the insulating oil is performed as a method for grasping the flow chargeability without stopping. The relationship between the winding leakage current and the charging degree of the insulating oil is shown in 2-2-2 [Relationship between the neutral point winding leakage current and the flow charge] on pages 72 to 73 of Non-Patent Document 1.

  A method for measuring the charging degree of the insulating oil is shown in 7-2-1 [Charging degree measuring method] in Chapter III [Measuring technique] of Part III, page 133 of Non-Patent Document 1. Various types of charge measurement devices have been developed in Japan and overseas, but different evaluation methods have been adopted for each equipment manufacturer, and they have not been performed in a unified manner, but are not patented. The mini electrostatic tester shown in FIG. 7-2-5 on page 133 of Document 1 is used in a relatively large number of engines. This mini electrostatic tester was devised to measure the charge level of jet fuel. For oil-filled electrical equipment, a filter for the static electricity generation part is used for fluid charging in the oil-filled electrical equipment (transformer). It is a cellulosic paper filter that can be captured, and is widely used because it is easy to manufacture and excellent in reproducibility.

  Factors affecting flow electrification of oil-filled electrical equipment (transformers), including the magnitude and temperature of the AC electric field applied to the windings, volume resistivity of insulating oil, dielectric loss tangent, moisture content in oil, and contained in insulating oil Non-Patent Document 1, pages 74 to 86, explain these factors and the influence on the degree of charge.

As a method of suppressing fluid charging phenomenon of oil-filled electrical equipment, fluid charging is suppressed by adding 1,2,3-benzotriazole (hereinafter referred to as BTA) to insulating oil on page 80 of Non-Patent Document 1. Is described. The data shows that when BTA is added, the degree of charge decreases from an addition amount of 5 ppm. Further, it is shown that when the addition amount is 30 ppm or less, the volume resistivity of the insulating oil, the dielectric breakdown voltage, and the dielectric strength of the oil-immersion coil model are not lowered.
In addition, as an example showing the effect of adding BTA in an actual transformer, BTA in oil is gradually adsorbed by an insulator or metallic copper and decreases with time, but the oil charge and dielectric loss tangent Data with a smaller increase is shown.

  As described above, in the state of the background art for the flow electrification phenomenon of oil-filled electrical equipment (transformers) and countermeasures, in oil-filled electrical equipment, BTA is used to suppress the dissolution of copper into insulating oil. Patent Document 1 discloses that 0.5 to 30 mg / l (liter) is added, and 2.6 ditertiary butylparacresol (hereinafter referred to as DBPC) is added as an oxidative degradation inhibitor.

Further, Patent Document 2 discloses a configuration in which the occurrence state of a flow electrification phenomenon is constantly monitored in an oil-filled electrical device, and the amount of static electricity generated is suppressed when there is a possibility of static electricity failure.
As shown in FIG. 1 of Patent Document 2, the configuration of Patent Document 2 includes a static induction device (oil-filled electricity) that includes a flow charge generation unit and a static electricity detection unit provided downstream thereof. Equipment) is placed close to the top of the tank, and the static charge generator's flow charge generator is covered with the same insulating material used in the tank, and is stationary between the electrodes to which an alternating electric field is applied Insulating liquid (insulating oil) flowing from the upper part of the induction tank is made to flow, and means for measuring the temperature and flow rate of the insulating liquid are provided, and these are determined from the magnitude of the alternating electric field of the flow charge generation unit. Comparing the allowable static electricity generation amount with the static electricity generation amount measured by the static electricity detection unit of the static electricity monitoring device, it is equipped with a comparison / determination unit that issues a warning when the latter value is greater than the former. liquid In which it has a mechanism for injecting an insulating liquid of containing middle high concentration charging inhibitor cooling circulation circuit.

  In the configuration of Patent Document 2, the flow charge is caused in consideration of conditions close to the inside of the static induction appliance, that is, the flow velocity, temperature, and the magnitude of the alternating electric field, and the amount of generated static electricity is adjusted by the static electricity detection unit. Yes, the static charge can be accurately estimated and the comparison / determination unit can determine whether or not there is a possibility of static electricity failure. Since the insulating liquid to which the substance is added is injected, static electricity inside the static induction appliance is suppressed, and electrostatic discharge due to charge accumulation or an insulation breakdown accident resulting therefrom can be prevented beforehand.

  The countermeasures against flow electrification of conventional oil-filled electrical equipment are as described above, and at the equipment design stage, the flow rate of the insulating oil is moderately controlled and consideration is given to eliminate local flow disturbance in the flow path. The use of a conservator as a diaphragm type suppresses oxygen intrusion during use and carefully selects the insulating material to be used. For insulating oil, proper management of moisture content, volume resistivity, dielectric loss tangent, etc. is performed. However, BTA is added to increase the degree of electrification over time.

Electric cooperative research, Vol. 54, No. 5, (Part 1) "Maintenance management of oil-filled transformers" JP-A-6-76635 JP 7-161534 A

The countermeasures against the flow electrification phenomenon of the conventional oil-filled electrical equipment are in the above situation, and it is assumed that the management of the production stage is strictly performed.
However, in actual oil-filled electrical equipment, as shown in Non-Patent Document 1, when a newly installed oil-filled electrical equipment is put into actual use, it has been shown that the flow charge increases with the course of use. The change in flow electrification over time is grasped by periodic measurement of winding leakage current, measurement of insulation oil charge, moisture content of insulation oil, measurement of dielectric loss tangent, etc. This is a situation that has not been studied much with respect to changes in components and changes in solid insulators.
Thus, since the substance produced | generated with respect to the change of the flow charge with the aging of the conventional oil-filled electrical equipment is not grasped | ascertained, there existed a problem that the exact suppression measure with respect to flow charge cannot be implemented.

  The present invention has been made to solve the above-mentioned problems, paying attention to a specific component contained in insulating oil of an oil-filled electrical device, and grasping a product generated by oxidation or the like of the specific component It is an object of the present invention to provide a method for diagnosing fluid charging of an oil-filled electrical device and a method for suppressing fluid charge of an oil-filled electrical device based on the diagnosis result.

Insulating oil contains sulfur compounds present in insulating oil filled in oil-filled electrical equipment, sulfur oxides generated by oxidation of sulfur compounds, nitrogen compounds, and nitrogen oxides generated by oxidation of nitrogen compounds Detects sulfur oxides or metal complexes of sulfur oxides, nitrogen compounds or metal complexes of nitrogen oxides, and aldehyde group concentrations and carboxyl group concentrations present in insulators, and detects the aldehyde groups. Using the concentration and the carboxyl group concentration as an index of flow chargeability, the flow chargeability of the oil-filled electrical device and the solid insulator inside thereof is diagnosed .

Insulating oil contains sulfur compounds present in insulating oil filled in oil-filled electrical equipment, sulfur oxides generated by oxidation of sulfur compounds, nitrogen compounds, and nitrogen oxides generated by oxidation of nitrogen compounds Detects sulfur oxides or metal complexes of sulfur oxides, nitrogen compounds or metal complexes of nitrogen oxides, and aldehyde group concentrations and carboxyl group concentrations present in insulators, and detects the aldehyde groups. The flow chargeability of the oil-filled electrical device and the solid insulator inside the oil-filled electrical device is diagnosed using the concentration and the carboxyl group concentration as an index of flow chargeability. it can.

Embodiment 1 FIG.
Oil-filled electrical equipment is refined so that the insulating oil to be filled has less components that affect flow charging, and design considerations such as suppressing the flow of insulating oil to an appropriate flow rate so that the flow charging phenomenon does not occur. Therefore, the flow chargeability at the initial stage of operation does not seem to be a problem. However, when it enters the operating state, a small amount of sulfur compounds and nitrogen compounds contained in the filled insulating oil react with a small amount of air components (oxygen and nitrogen) contained in the initial stage to form sulfur oxides and nitrogen oxides. Furthermore, the copper material of the conductor material in the oil-filled electrical device works as a copper catalyst, and the reaction proceeds to generate a highly charged substance. Oil-filled electrical equipment has a problem that an increase phenomenon of flow electrification occurs with the passage of operation time.
The first embodiment provides a fluid charging diagnostic method for an oil-filled electrical device that diagnoses the flow chargeability without stopping the operation in the actual operation stage of the oil-filled electrical device.

Before explaining the flow electrification phenomenon, the general properties of the filled insulating oil will be explained.
The insulating oil filled in oil-filled electrical equipment varies considerably depending on the crude oil production area, but the elemental composition falls within the following range.
Carbon 82-87% Hydrogen 11-15%
Sulfur 0.1-5% Nitrogen 0.1-5%
Oxygen 0.1-2% Metal 0-0.5%
Thus, most of the crude oil is petroleum hydrocarbons consisting of carbon and hydrogen. Hydrocarbons contained in mineral insulating oils are composed of many extremely complicated isomers, so it is impossible to know the chemical structure of each, but the chemical structure of the main hydrocarbon component is a chain. It is classified into three types: paraffinic hydrocarbons with a structure connected in the form of a ring, naphthenic hydrocarbons connected in a ring, and aromatic hydrocarbons with a benzene ring.
Non-hydrocarbon sulfur compounds, nitrogen compounds, oxygen compounds, etc. contained in crude oil are less than hydrocarbons, but they are moderately removed by the refining process because they have a significant effect on the quality of insulating oil. .

Insulating oil used in oil-filled electrical equipment is a refined mineral oil that contains 0.1-0.5% sulfur compounds as sulfur components and exists in the following order: .
Thiophenes >>Sulphides>Disulfides> Mercaptan (thiol) s

The molecular structure of the sulfur compound contained in the insulating oil is shown in FIG. 1A shows a typical structural formula of benzothiophene, and FIG. 1B shows a typical structural formula of dibenzothiophene. Benzothiophene has a structure in which a benzene ring is adjacent to a 5-membered thiophene ring, while dibenzothiophene is sandwiched between two benzene rings and has a thiophene ring. A sulfur atom exists in the position which does not share a bond with a benzene ring.
In both cases of benzothiophene and dibenzothiophene, an alkyl group which is a chain hydrocarbon is substituted with a part of the benzene ring or thiophene ring. Therefore, the thiophenes present in the insulating oil exist with a certain molecular weight distribution, and combinations thereof are nearly infinite.

The next most common thiophenes are sulfides. The structural formula of the sulfide compound is shown in FIG. This structure has a structure in which alkyl groups are arranged at both ends of a sulfur atom. In the experiment, n = m of a commercially available reagent, that is, a compound having the same carbon number on both sides was used. Actually, n and m are not necessarily equal, and even with the same n and m, various structures can be adopted depending on the state of branching of the molecular chain, so that there are infinite combinations.
The sulfide compound is a divalent sulfur compound and has an electron (lone electron pair) that does not participate in bonding. Therefore, it easily reacts with an active compound such as peroxide to form the tetravalent sulfoxide compound of FIG. 1 (d) and the hexavalent sulfone compound of FIG. 1 (e).

  FIG. 1 (f) shows the molecular structure of disulfide. This is a structure in which an alkyl group is present at both ends of a disulfide (—SS—) bond.

 FIG. 1 (g) shows the molecular structure of the thiol compound. This is also called a mercaptan, and one end of the sulfur atom is composed of an alkyl group and the other end is composed of a hydrogen atom. Alcohol compounds replace sulfur with oxygen. The part surrounded by a broken line has a structure common to sulfides.

Next, the concept of fluid charging in an oil-filled electrical device during operation will be described.
When the oil-filled electrical device is operated, as shown in FIG. 2, the insulating oil and the substance A (sulfur compound, nitrogen compound, etc.) contained in the insulating oil remain in the insulating oil and heat due to the temperature rise inside the device. It changes to substance B (sulfur oxide, nitrogen oxide, etc.) under the influence of the catalytic action of copper on conductive materials such as oxygen and coil, and substance B has a molecular structure due to the catalytic action due to the presence of copper and bonding with copper. A stable metal complex or the like. It is assumed that the charge of the insulating oil increases due to the generation of the highly charged substance due to the change in the components contained by the operation.

  The insulation paper covering the surface of the inner conductor and the solid insulation of the press board placed between the coil and the iron core or tank are all materials mainly composed of cellulose. The degree of electrification advances due to the secular change due to the oxidation of the substance and the adsorption of substances present inside. BTA has the function of adsorbing with the insulating paper to suppress the negative charge transfer on the surface of the insulating paper and inactivating the catalytic effect on the copper surface.

In order to find a diagnostic method for diagnosing the possibility of fluid charging phenomenon during operation of oil-filled electrical equipment, and to select a suppression method when there is a possibility of fluid charging phenomenon, the following items should be clarified: is necessary.
(1) Clarification of precursor substance (substance A) that causes increase in charge level (2) Clarification of increase substance (substance B) that causes increase in charge degree (3) Clarification of acceleration factors from precursor substance to increase substance ( (Copper catalyst, oxygen, heat, etc.)
Next, it is necessary to find a suppression method when the fluid charging phenomenon occurs and to solve the following problem in order to confirm the effect of the suppression method.
(4) Creation of a method to suppress changes from precursor substances to increased substances and confirmation of their effects (addition of BTA, DBPC, etc. and confirmation of their effects)
(5) Establishment of removal method for increased substances (oil treatment for oil-filled electrical equipment)
(6) Establishment of analysis methods for precursors and increased substances

In order to clarify the diagnosis method and suppression method of the fluid charging phenomenon, sulfur compounds, nitrogen compounds, etc. contained in the insulating oil are targeted, added to the insulating oil to be tested for each substance present in the insulating oil, A heating test was conducted as a condition close to the environmental conditions inside the actual oil-filled electrical equipment.
(1) Test conditions / Test oil: Alkylbenzene Since mineral oil-based insulation oil contains many kinds of trace components, testing for trace components using insulation oil itself will reduce test accuracy. Alkylbenzene was used as a synthetic oil having the same molecular weight and characteristics as mineral insulating oil. (Since alkylbenzene is composed only of hydrocarbons, the addition accuracy of sulfur, nitrogen and oxygen trace components is increased.
Test container: inner volume 450-500 ml (ml = milliliter), with bellows.
A substance with an influence on the degree of charge was added to the test oil, and a structure with a bellows was made in consideration of being able to secure a gas space inside and withstanding temperature changes in a sealed state. FIG. 3 shows the configuration of the test container.
Sample configuration: When a space was provided for the addition of oxygen, the test oil was 450 ml, the space was 50 ml, and a copper wire simulating the winding material was 1 mm straight and 9.5 m long. The surface area of this copper wire is about 300 cm ² and is 66 cm ² for 100 ml of insulating oil.
When no space was provided, the test oil was 450 ml.
・ Heating conditions: Heating temperature ・ ・ 120 ℃, Heating time ・ ・ Maximum 450Hr
Charge degree measuring device: A mini electrostatic tester shown in FIG. The configuration diagram is shown in FIG. In the test method, one sample oil is measured four times with one filter, and the average value of three times excluding the first is taken as the degree of charge and converted to 20 ° C.
-Conditions for substance addition: FIG. 5 shows a list of compounds used in the addition test of the components contained in the insulating oil. FIG. 5 also shows the compounds used in the tests in the second and subsequent embodiments. The sulfur compound was dissolved in alkylbenzene so that the average sulfur compound concentration contained in ordinary mineral insulating oil was 86 ppm in terms of sulfur content.
Regarding the copper compound, the copper concentration was adjusted to 10 ppm, and the oxygen compound and the nitrogen compound were added and dissolved so that the functional group (component other than hydrocarbon) was 86 ppm.
-Oxygen and copper catalyst conditions affecting the flow electrification phenomenon: The following conditions were set and an addition test was conducted for each condition.
Condition 1: System containing no oxygen and copper catalyst Condition 2: System containing oxygen and no copper catalyst Condition 3: System containing no oxygen and a copper catalyst Condition 4: System containing oxygen and a copper catalyst

・ Additive substances: Select substances that are contained in insulating oil filled in oil-filled electrical equipment and that may be involved in fluid charging phenomenon.
Sulfur compounds: sulfides, disulfides, sulfoxides, sulfones, thiophenes, thiols and the like.

<Evaluation of flow chargeability of sulfides>
With respect to the sulfides shown in FIG. 5 of the sulfides contained in the insulating oil, a heating test was carried out under the above test conditions, and the charge degree of the test oil after heating was evaluated.
The following experimental data 1 is a blank test in which no sulfides are added to the alkylbenzene of the test oil. As representatives of sulfides, experimental data 2 shows the case of heptyl sulfide, and experimental data 3 shows the case of dodecyl sulfide. Tests are similarly conducted for the sulfides other than heptyl sulfide and dodecyl sulfide shown in FIG. Experimental data 4 shows the relationship between the degree of charge and the molecular weight (carbon number) after 100 hours of heating in the heating test for each sulfide.

<Experimental data 1> Heat test of only the alkylbenzene of the insulating oil used in the test The test results are shown in FIG.
The test results show that the degree of charge hardly increases with respect to the conditions of oxygen and copper catalyst.

<Experimental data 2> Heat test for addition of heptyl sulfide to sulfide sulfur compound As a representative example of the heat test for sulfide sulfur compound, 620 ppm of heptyl sulfide is added to alkylbenzene, heated for 450 hours under the above test conditions, and the degree of charge after heating. FIG. 7 shows the result of the heating test for determining the change in the.
The results are as follows.
Condition 1: System not containing oxygen and copper catalyst: Little increase in charge.
Condition 2: A system containing oxygen and not containing a copper catalyst: The increase in charging degree is very small.
Condition 3: a system containing no copper and containing a copper catalyst: the degree of charging is rapidly increasing.
Condition 4: a system containing oxygen and a copper catalyst: the degree of charge is rapidly increasing.
From this result, in heptyl sulfide, an oxidation product of heptyl sulfide is generated by oxygen, and this oxidation product affects the increase in the degree of charge. It is presumed that the oxidation product of heptyl sulfide and copper were combined to produce a highly charged substance.

<Experimental data 3> Heat test for addition of sulfide sulfur compound dodecyl sulfide As a typical example of a sulfide sulfur compound heat test, 1000 ppm of dodecyl sulfide was added to alkylbenzene, heated for 450 hours under the above test conditions, and the degree of charge after heating. FIG. 8 shows the result of the heating test for determining the change in the temperature.
The results are as follows.
Condition 1: System not containing oxygen and copper catalyst: Little increase in charge.
Condition 2: A system containing oxygen and not containing a copper catalyst: The degree of charge tends to increase gradually.
Condition 3: A system containing no copper and containing a copper catalyst: the degree of charging is increasing.
Condition 4: a system containing oxygen and a copper catalyst: the degree of charge is rapidly increasing.
From this result, in the dodecyl sulfide, the oxidation product dodecyl sulfoxide is generated by oxygen, this dodecyl sulfoxide has an effect on the increase in the degree of charge, and the relationship between the copper catalyst and the case where the action as a catalyst is large, It is presumed that dodecyl sulfoxide and copper were combined to form a highly charged substance.

<Experimental data 4> Relationship data between carbon number (or molecular weight) of sulfides and charge degree For the sulfides in the compound list used in the test of FIG. With respect to the results under the above conditions, the horizontal axis indicates the number of carbon atoms (molecular weight), and the vertical axis indicates the degree of charge after a heating time of 100 hours. The relationship is as shown in FIG.
As for the situation, methyl sulfide or ethyl sulfide having a small number of carbon atoms (small molecular weight) among the sulfide compounds does not show a significant increase in the charge degree in the heating test. In addition, no significant increase in charge is observed even with tetradecyl sulfide having 14 carbon atoms.
The relationship between the number of carbon atoms and the degree of charge is such that the heptyl sulfide or octyl sulfide having 7 to 8 carbon atoms is the apex and decreases on both sides when the carbon number is small and when the carbon number is large.

In general, a sulfur atom has a large electronegativity and has an ability to attract electrons of other atoms. In the case of aromatic rings, the electrons are in excess. It is presumed that such an electron state in the vicinity of the sulfur atom affects the charging characteristics.
The reason why the vicinity of 8 carbon atoms is the apex is presumed to be that the compatibility of the insulating oil is difficult because methyl or ethyl has a small alkyl group that is compatible with the insulating oil. On the other hand, it is presumed that when the number of carbon atoms increases, reactions such as oxidation of sulfur atoms are inhibited by steric hindrance of the alkyl group. (Although it has a linear structure in terms of expression, since the carbon atoms are actually bonded at an angle of 109 °, the molecule is bent, and the alkyl group covers the periphery of the sulfur atom due to the bending. .) That is, it is presumed that the number of carbon atoms becomes the apex from both aspects of compatibility with insulating oil and inhibition of reactivity due to steric hindrance.

  The insulating oil contains a plurality of types of sulfides having different numbers of carbon atoms, and the degree of involvement in the degree of charge is different, so the degree of participation in the degree of charge for each of the sulfides shown in FIG. By multiplying the charge degree coefficient according to the above, it is possible to comprehensively determine the involvement of sulfides in the charge degree. For example, in the sulfides shown in FIG. 9, the amount of addition to the insulating oil is an amount corresponding to 86 ppm in terms of the sulfur content of the standard concentration of the sulfur compound contained in the normal mineral insulating oil. It is the data which was experimented. As shown in FIG. 10, the charge ratio of other sulfides is obtained by setting the charge degree of octyl sulfide having 16 carbon atoms (molecular weight 258) to 1, and the ratio of each charge degree of the detected sulfides is tabulated. The charge level of sulfides can be evaluated by multiplying the total value as the charge index value Y and multiplying the charge level of octyl sulfide as a reference. Appropriate evaluation can be made for different materials.

<Experimental data 5> Relationship between molecular weight or carbon number of sulfides and disulfides and charge degree State of adding molecular weight or carbon number and charge degree of disulfides to the relationship between molecular weight and carbon number of sulfides in FIG. Is shown in FIG. ◆ is sulfides, and □ is disulfides. Disulfides, like sulfides, are divalent sulfur compounds, but it is presumed that they do not become highly charged substances due to less oxygen uptake into the compounds.
Sulfides have an antioxidant effect on insulating oil, and have the function of inhibiting the propagation of oxidative degradation by incorporating oxygen in the peroxide into the molecule, but disulfides are said to be decomposed by peroxides and radicals. The difference between the two is presumed that the thioyl radicals produced by the decomposition of disulfides are involved in sulfidation corrosion.
RSR '+ R ”OOH → RSOR” + R ”OH
RSSR '+ R ”OOH → RSSR' + R” O ・ + ・ OH
→ RS ・ + R'S ・ + R ”OOH
(R, R ', R "are alkyl groups,.
Also, from the viewpoint of the sulfur bond, the S—S bond is estimated to be easily broken because it is longer than 2.04 Å and 1.78 Ｃ of the C—S bond.

<Experimental Data 6> Evaluation Data for Sulfoxides Sulfoxide is an oxidation product of sulfide represented by the following formula, and it reacts with peroxide oxygen rather than reacting directly with oxygen to form sulfoxide. It is considered to be. Sulfide is a divalent sulfur compound, and sulfoxide is a tetravalent sulfur compound.
R2S + R'OOH → R2S = O + R'OH
Sulfide sulfoxide
R2S = O + R'OOH → R2SO2 + R'OH
Sulfoxide sulfone

As described above, in the addition test of sulfides, an increase in charge was observed. Therefore, a confirmation test was performed to determine whether sulfoxides, which are oxidation products of sulfides, are substances having a high charge.
FIG. 12 shows the results of a heat test of butyl sulfoxide, a sulfoxide. The test conditions are the same as the experimental data 2.
As a result, when both oxygen and the copper catalyst are not present, the increase in the charging degree is small, but in the system where the copper catalyst coexists, the charging degree is increased. From this result, it is presumed that butyl sulfoxide is greatly changed to a highly charged substance by the copper catalyst.
FIG. 13 shows the dependency of the degree of charge of alkylbenzene added with butyl sulfoxide at normal temperature on the concentration of the additive. When the sulfoxide itself is a highly charged substance, the charge degree of alkylbenzene should increase only by adding the sulfoxide at room temperature. However, although it depends on the addition concentration, it is 140 pC even when added up to 900 ppm. It is estimated that the highly charged substance is not sulfoxide itself, because it is at a level exceeding about 1000 pC / ml as observed in the sulfide heat test.

<Experimental Data 7> Comparative Experiment of Sulfides, Sulfoxides, and Sulfones Oxygen and copper with a marked increase in charge as a result of the heating test under the test conditions described above for comparative experiments of butyl sulfides, sulfoxides, and sulfones FIG. 14 shows changes with time in a comparative display in the coexistence system of both catalysts.
The degree of charge after heating for 75 hours and the degree of charge after 100 hours increased for both butyl sulfide and butyl sulfoxide, but butyl sulfoxide tended to be higher than butyl sulfide, and butyl sulfone increased in charge. Not done. As described above, it is presumed that sulfoxide itself is not a highly charged substance as described above, but is more likely to be a highly charged substance than a sulfide compound in the presence of oxygen or a copper catalyst.

<Experimental data 8> Copper dissolution amount during heating test of sulfides, sulfoxides, and sulfones Heating when added for each of butyl sulfide, butyl sulfoxide, and butyl sulfone according to the presence or absence of oxygen during the heating test shown in experimental data 6 The amount of copper dissolved after time is shown in FIG. Butyl sulfoxide is dissolved in a large amount with oxygen, and is about 1/2 that without oxygen without oxygen. Butyl sulfide is similar to butylsulfoxide without oxygen, with or without oxygen.

<Experimental data 9> Heat test of sulfones Sulfones are oxidation products of sulfoxides represented by the following formula. The original compounds, whether sulfoxides or sulfones, are sulfides. In the same manner as when sulfoxides are formed, it is considered that sulfoxides react with oxygen of peroxide to become sulfones rather than directly react with oxygen to become sulfones. Sulfides are divalent and sulfoxides are tetravalent, but sulfones are hexavalent sulfur compounds. In the case of sulfones, since the sulfur atom is hexavalent, further loading reaction cannot be performed.
R2S + R'OOH → R2S = O + R'OH
Sulfides Sulfoxides
R2S = O + R'OOH → R2SO2 + R'OH
Sulfoxides Sulfones

  The result of the heating test for the addition of sulfones is shown in FIG. As a result, no increase in the degree of charging was observed in the heating test. The behavior is different from sulfides and sulfoxides, and there is almost no influence of oxygen and copper catalyst. In sulfides and sulfoxides, there is a tendency to increase the charge in the presence of oxygen and a copper catalyst, whereas in sulfones, the charge is increasing in the absence of oxygen and a copper catalyst, but the increase is markedly increased. However, since the increase in the charging degree is not observed even in the heating test, it is not considered to be an intermediate of the highly charged substance.

<Experimental data 10> Heat test of addition of thiophenes The main component of the sulfur compound contained in the insulating oil is thiophenes, and the results of a heat test in which benzothiophenes of the thiophenes are added are shown in FIG. The test conditions are the same as in experimental data 2. When the heating time is 450 hours, the charging degree converges to 100 to 200 pC / ml, and no increase tendency is observed. Moreover, it is thought that it is a substance hardly affected by the copper catalyst.

<Experimental data 11> Heat test of addition of thiols Thiols belong to a relatively small amount of sulfur compounds in insulating oil. The chemical formula is as shown in FIG. 1 (g), and the portion surrounded by a broken line is similar to the sulfide compound. One of the sulfur atoms is bonded to a hydrogen atom, but may have characteristics similar to those of sulfide compounds. FIG. 18 is a test result with an oxygen and copper catalyst in a heating test in which 390 ppm of thiol octanethiol was added.
As a result, when the heating time is 100 hours, the charging degree is 2000 pC / ml, which is two digits higher than the initial value.

<Experimental Data 12> Relationship Data Between Carbon Number (or Molecular Weight) and Charge Level of Thiols FIG. 19 is a diagram showing the relationship between the carbon number (or molecular weight) of thiols and the charge level. Although the number of data is small, like the sulfides, it shows a tendency that octanethiol having 8 carbon atoms is at the top. The butyl sulfide sulfide has an increase in charge, but the thiol butanethiol (carbon number 4) has a heating time of 100 hours and exhibits a negative charge. T-Dodecanethiol (carbon number 12) having a long alkyl group results in no increase in charge even when the heating time elapses. The increase in the degree of charge of octanethiol (carbon number 8) is similar to sulfides. Sulfides (RSR) and thiols (RSH) are similar, and thiols are those in which R ′ is replaced by H, and are involved in increasing the degree of charge. Similar to doing.

<Evaluation of flow chargeability of nitrogen compounds>
Insulating oil contains a nitrogen compound in a smaller amount than the sulfur compound. There are few nitrogen compounds bonded to chain hydrocarbons, and they are roughly classified into compounds having an aromatic ring such as indoles, imidazoles, pyridines, quinolines, and carbazoles.
<Experimental data 13>
FIG. 20 shows the results of a heating test in which 718 ppm of indole indole was added to insulating oil. The test conditions are the same as in experimental data 2.
Test results do not show high charge. On the other hand, when heated for 100 hours, it exhibits negative polarity and is different from the sulfides of sulfur compounds.

<Evaluation of fluid chargeability of oxygen compounds>
<Experimental data 14>
There are very few oxygen compounds present in the new insulating oil, but when the insulating oil is oxidized and deteriorated, oxygen compounds such as alcohols, aldehydes, ketones, and organic acids may be generated. Addition tests were conducted on various oxygen compounds, but no compounds that lead to an increase in the degree of charge were found. Detailed data is omitted.

<Diagnosis method for flow chargeability of oil-filled electrical equipment>
As described above, as a result of conducting a heating test on the inclusion substances that may be present in the insulating oil under the combined conditions of the presence or absence of oxygen and the presence or absence of the copper catalyst, the oxygen in the oil-filled electrical equipment, the copper catalyst In a heating test under a certain condition, data indicating that the degree of charge is large in a heating test of sulfides and sulfoxides and thiols of oxidation products thereof are obtained. The charge level for other materials is a low result.
Based on these results, based on the amount of sulfur component contained in the normal insulating oil of oil-filled electrical equipment, the substance that may be present in the insulating oil is used as the indicator substance, and the charge degree of the insulating oil for the indicator substance in advance. Investigate the state involved in the substance for each substance, extract the insulating oil filled from the oil-filled electrical equipment based on this, analyze the substance contained in the extracted insulating oil, and the substance involved in the fluid charging phenomenon By comparing the presence / absence of water and the level of the reference value when it exists, the fluidized charging phenomenon can be diagnosed without stopping the oil-filled electrical device.

  As described above, the influence of the components present in the insulating oil filled in the oil-filled electrical equipment on the flow charging phenomenon and the state of change of the components are clarified, and the components that greatly affect the flow charging phenomenon are indicated as indicator substances. Insulating oil of an oil-filled electrical device that is actually in operation can be collected, the contained component can be analyzed, and the flow chargeability of the oil-filled electrical device can be diagnosed based on the amount of the contained component used as an indicator substance.

  In addition, the degree of participation in the insulating oil charge of the substance used as the indicator substance differs depending on the substance. Therefore, for accurate diagnosis, the substance with the largest contribution to charge formation is used as a reference, and other substances The charge ratios of the same standard are calculated, the charge ratios of the detected substances are totaled, the calculated value is used as the charge index value, and the reference substance amount is multiplied, and the set charge limit is set. In comparison, it is possible to diagnose the flow chargeability of the oil-filled electrical device.

  In the above description, in order to diagnose the flow chargeability of oil-filled electrical equipment, the sulfur compounds sulfides and sulfur oxide sulfoxides that are largely involved in flow charge are used as indicators. When the fluid chargeability diagnosis is performed using a sulfur oxide metal complex or a nitrogen oxide metal complex formed as an indicator substance, it is possible to estimate a detailed cause of the charge.

Embodiment 2. FIG.
In the first embodiment, the oxygen contained in the insulating oil filled in the oil-filled electrical device and the aspect of increasing the charging degree by the copper catalyst have been described. However, the substance involved in increasing the charging degree was detected. In some cases, or when it is found that the increase in the degree of charge has progressed, it is necessary to suppress the increase in the degree of charge. The second embodiment shows a method for suppressing the increase in the degree of charge.

<Evaluation of fluid charging suppression effect on sulfides of BTA and DBPC>
BTA (benzotriazole) is filled in order to suppress the increase in the charging degree of oil-filled electrical equipment, but this is adsorbed on the insulating paper and has the effect of suppressing the negative charge transfer to the insulating paper surface. It is filled with the fact that it has a function to inactivate the copper surface.

<Experimental data 15> Heat test when BTA is added to sulfides A heat test was carried out to determine how much the BTA is a sulfur compound with respect to increasing the degree of charge of sulfides. FIG. 21 shows the results of a heating test in the case of adding 1000 ppm of sulfides dodecyl sulfide and 30 mg / 1 of BTA. The test conditions are the same as in experimental data 2.
As a result, the degree of charging is low regardless of the presence or absence of oxygen and a copper catalyst.

<Experimental data 16> Heat test in the case of adding BTA to sulfides A heat test was carried out as to how much the BTA has a suppressive effect on the increase in the degree of charge of sulfides which are sulfur compounds. FIG. 22 shows the results of a heating test in the case of adding 620 ppm of heptyl sulfide sulfide and 30 mg / 1 of BTA. The test conditions are the same as in experimental data 2.
As a result, the degree of charging is low regardless of the presence or absence of oxygen and a copper catalyst.

<Experimental data 17> Heating test in the case of adding DBPC to sulfides A heating test was carried out as to how much the DBPC is effective for increasing the degree of charge of sulfides which are sulfur compounds. FIG. 23 shows the results of a heating test in the case of adding 620 ppm of heptyl sulfide sulfide and 3000 mg / l of DBPC. The test conditions are the same as in experimental data 2.
As a result, there is no tendency to increase the degree of charging regardless of the presence or absence of oxygen and a copper catalyst. This is presumed that DBPC suppresses the oxidation reaction of sulfide.

<Experimental data 18> Heat test when sulfoxides and BTA or DBPC are added When BTA or DBPC is added to butyl sulfoxide of sulfoxides of sulfur oxides, what is the inhibitory effect on increasing the degree of charge? A heating test was conducted. FIG. 24 shows the results of a heating test in the case of adding 450 ppm of butyl sulfoxide of sulfoxides and 30 mg / l of BTA or 3000 mg / l of DBPC. The test conditions are the same as in experimental data 2.
As a result, when BTA and DBPC were not added, the charging degree was remarkably increased, whereas when BTA was added, there was no increase in charging degree. An increase in charge was observed up to the same level as when no BTA or DBPC was added.
In this experimental data, BTA is effective in suppressing the increase in the charge degree of sulfoxide, but DBPC suppresses the reaction in which sulfide is changed into sulfoxide, but does not show the effect of suppressing the high charge degree.

<Evaluation of the effect of suppressing flow electrification by nitrogen compounds>
The heating test for indole nitrogen compounds is shown in the experimental data 13 of the first embodiment. However, this does not show a high degree of charge, and conversely, when heated for 100 hours, it exhibits a negative polarity and is highly charged like a sulfur compound. Although it was shown that it was not a substance to be heated, imidazoles, quinolines, carbazoles and the like of the same nitrogen compound were also subjected to a heating test.
<Experimental data 19> Heat test of benzimidazole FIG. 25 shows the result of a heat test in which 362 ppm of imidazole benzimidazole was added to insulating oil. The test conditions are the same as in experimental data 2.
The test result is a result of being negatively charged as the heating time elapses.
<Experimental Data 20> Heat Test of 8 Hydroxyquinoline FIG. 26 shows the results of a heat test in which 891 ppm of 8 hydroxyquinoline was added to insulating oil. The test conditions are the same as in experimental data 2.
The test results show positive polarity at the initial stage of heating, but when the heating time has passed, the test has turned negative.

Experimental data 13 indole, experimental data 19 benzimidazole, and experimental data 20 hydroxyquinoline are negatively charged when heated in insulating oil, such as sulfides of sulfur compounds and sulfoxides of sulfur oxides. In the case where a substance having an increased charge is present, if an appropriate amount is added, it is possible to suppress the increase in the charge over time by offsetting the flow charge by sulfides and sulfoxides.
When the flow chargeability is examined by adding a nitrogen compound, the charge is preferably in the vicinity of 0 pC / ml, and it is important to make the addition amount strict so as not to increase the negative polarity.

Embodiment 3 FIG.
In the first embodiment, the property of the substance that causes the fluid charging phenomenon will be explained and a fluid charging diagnosis method will be shown. In the second embodiment, the insulating oil filled in the oil-filled electrical device is increased in charge. Although the suppression method when the degree of electrification becomes high is shown, this Embodiment 3 shows a method for removing a substance that increases the degree of electrification in the insulating oil.
The fluid electrification phenomenon of the insulating oil involves a highly charged substance such as sulfides of sulfur compounds and sulfoxides of sulfur oxides which are oxides thereof. If this highly charged substance can be removed, fluid charging of the oil-filled electrical device can be suppressed.

Conducted experiments to remove highly charged substances using activated clay for adsorbents used for purification of insulating oil, activated carbon used for purification of solvents and gases, and silica gel for analytical tests (Wakogel 200). It was.
<Experimental data 19> Removal treatment experiment of highly charged substance in insulating oil The above three kinds of adsorbents were heated and dried at 100 ° C. for 24 hours, and 45 g of the dried adsorbent was weighed and put into 300 ml of insulating oil. Then, the mixture was stirred for 1 hour in a light-shielded state, filtered, and then vacuum degassed, and the degree of charge was measured with a mini electrostatic tester disclosed in Non-Patent Document 1.
Insulating oil is alkylbenzene, 1037 ppm of dodecyl sulfoxide, a sulfoxide of highly charged substance, is added, and a heated sample of 100 hours, a heated sample of 250 hours, and a heated sample of 450 hours are prepared. After measuring the charge degree individually, the two tanks were mixed and the removal process of the highly charged substance was performed with the adsorbent.

Test results For reference, FIG. 27 shows data of a heating test conducted under a combination of the presence or absence of oxygen and the presence or absence of a copper catalyst in alkylbenzene added with 1037 ppm of dodecylbenzene. FIG. 28 shows comparison data of the degree of charge before and after the treatment for each adsorbent type. In addition, FIG. 29 shows the measurement results of the degree of charge and the amount of copper dissolved in oil. FIG. 30 illustrates the data of FIG. FIG. 31 is a graph showing the degree of charge before the treatment of each adsorbent and the change in the degree of charge after the treatment of each adsorbent after heating times of 100 hours, 250 hours, and 450 hours.

<Consideration of results>
Any adsorbent in the order of activated clay, activated carbon and silica gel for analytical test showed the effect of removing highly charged substances.
As for the effect, the one treated with activated clay shows a lower value than the charge of the initial insulating oil, and the one treated with activated carbon shows a value almost equal to the charge of the initial insulating oil. The value is about one digit higher than the initial charging degree.

  As shown in the results, it is possible to remove the highly charged substance and dissolved copper from the insulating oil in which the highly charged substance is produced by performing activated clay treatment and activated carbon treatment. When the increase in the degree of charging progresses in the input electrical equipment, the increase in the charging degree can be suppressed by performing the activated clay treatment and the activated carbon treatment.

  In an actual oil-filled electrical device, a circulation circuit is formed by piping between the device body and the cooler, and an insulating oil whose charging degree has been increased by placing an adsorbent in the insulation oil circulation circuit. Highly charged substances in the medium can be adsorbed and removed.

Embodiment 4 FIG.
The flow electrification of the oil-filled electrical device occurs between the solid insulator of the press board or the insulating paper in the oil-filled electrical device and the insulating oil. Insulator paper covering the surface of the inner conductor and the insulation of the press board, which is located between the coil and the iron core or tank, are all materials mainly composed of cellulose. The degree of electrification advances due to the secular change due to the oxidation of the substance and the adsorption of substances present inside. As factors of aging of insulating paper and press board of solid insulator, oxidation of cellulose and adsorption of components in oil onto the insulator surface are considered.
When cellulose is oxidized, some hydroxyl groups are converted to carboxyl groups via aldehyde groups. The hydroxyl group is composed of an oxygen atom and a hydrogen atom. Oxygen is negatively polarized and hydrogen is positively polarized, and the degree of polarization is in the order of [hydroxyl group <aldehyde group <carboxyl group]. The larger the polarization, the stronger the force to take in negative charges, and the more easily charged.

FIG. 32 shows the relationship between the amount of carboxyl groups in the insulating oil and the degree of charge. As the amount of carboxyl groups increases, the degree of charge tends to increase.
Aldehyde groups and carboxyl groups generated by oxidation of insulating paper and press board are also dissolved in insulating oil, so aldehyde group concentration and carboxyl group concentration in insulating oil are detected, and this is used as an index value. By setting the limit value, it is possible to diagnose the flow charge of the solid insulating portion of the oil-filled electrical device.

Embodiment 5 FIG.
FIG. 33 shows the charging characteristics after impregnating insulating oils having different charging characteristics on the filter paper used in the static electricity generation part of the electrostatic minitester for examining the charging degree of the insulating oil. The horizontal axis represents the charging degree of the impregnating oil, and the vertical axis represents the rate of increase or decrease in the charging rate of the insulator expressed by the following equation.
Insulator charge degree increase / decrease rate = (AB) / B
A: Charge when a filter paper impregnated with insulating oil is used as a static electricity generating part B: Charge when a new filter paper is used as a static electricity generating part In this method, the relationship between the internal conditions of the oil-filled electrical device and the impregnated oil in advance By organizing the data so that they are equivalent, it is possible to perform flow charge diagnosis of oil-filled electrical equipment.

  By making the filter paper detachable in the flow path of the insulating oil of the actual oil-filled electrical device, it is possible to diagnose the flow chargeability without stopping the oil-filled electrical device.

Embodiment 6 FIG.
FIG. 34 shows the relationship between dissolved nitrogen gas concentration in insulating oil collected from oil-filled electrical equipment and sulfoxide / sulfide. In this data, the sulfoxide / sulfide tends to increase when the nitrogen gas concentration is high.

  If oxygen or nitrogen as an air component is present in the oil-filled electrical device, oxygen is consumed for the oxidation reaction in the oil-filled electrical device, but the inert nitrogen gas is dissolved as it is. Therefore, when a large amount of nitrogen gas is contained in the oil-filled electrical device, this indicates that there is a large amount of invaded air, which means that the oxidation reaction in the oil-filled electrical device further progresses. By detecting the amount of nitrogen gas in the insulating oil, the sulfoxide / sulfide ratio increases, and the state of flow charge in the oil-filled electrical device can be diagnosed.

It is a figure which shows the molecular structure of the sulfur compound which exists in insulating oil. It is a conceptual explanatory view of increasing the degree of charging of insulating oil and insulator in an oil-filled electrical device. It is a block diagram of the test container used for the heating test. It is a block diagram of the mini electrostatic tester used for the heating test. It is a list of the compounds used for the addition test of the component contained in insulating oil. It is a test result of the heating test of the alkylbenzene used alone for the test. It is a test result of the heating test of heptyl sulfide addition. It is a test result of the heating test of dodecyl sulfide addition. This data shows the relationship between the number of carbons (molecular weight) of sulfides and the degree of charge. It is a conversion ratio table which converts the charge degree for every substance of sulfides into a reference substance. This data shows the charge degree of each substance obtained by adding the relationship between the carbon number of the disulfides and the charge degree to the relation between the carbon number of the sulfides and the charge degree. It is the result of the heating test of butyl sulfoxide addition It is a figure which shows the addition density | concentration dependence of the charging degree of the alkylbenzene which added butyl sulfoxide at normal temperature. It is a result of the comparative experiment of sulfides, sulfoxides, and sulfones. It is a figure which shows the copper dissolution amount at the time of the heat test of sulfides, sulfoxides, and sulfones. It is a test result of the heating test of sulfones addition. It is a test result of the heating test of benzothiophene addition. It is a test result of the heating test of octanethiol addition. It is a figure which shows the relationship between the carbon number of thiols, and a charging degree. It is a test result of the heating test of indole addition. It is a test result of the heating test at the time of adding dodecyl sulfide and BTA. It is a test result of the heating test at the time of adding heptyl sulfide and BTA. It is a test result of the heating test at the time of adding heptyl sulfide and DBPC. It is a test result of the heating test at the time of adding butyl sulfoxide and BTA or DBPC. It is a test result of the heating test of benzimidazole addition. It is a test result of the heat test of adding 8 hydroquinoline. It is a test result of the heating test performed on the combined conditions of the presence or absence of oxygen and the presence or absence of a copper catalyst in the alkylbenzene added with dodecylbenzene. It is the comparison data of the charge degree before and after the process for every kind of adsorbent, and copper amount. It is the data which shows the change of the electrification degree after the process of each adsorbent in the charge degree before the process of an adsorbent, and the heating time after 100 hours, 250 hours, and 450 hours. It is the result of the charge degree before the treatment of the adsorbent and the charge degree after the treatment of each adsorbent after the heating time of 100 hours, 250 hours, and 450 hours. It is a graph which shows the change of the charge degree after the process of adsorption agent. It is a figure which shows the relationship between the carboxyl group amount of an insulating paper, and a charging degree. It is a figure which shows the charging degree increase / decrease rate of an oil impregnation insulator. It is a figure which shows the relationship between the nitrogen gas density | concentration of insulating oil, and a sulfoxide / sulfide.

Claims (1)

Insulating oil contains sulfur compounds present in insulating oil filled in oil-filled electrical equipment, sulfur oxides generated by oxidation of sulfur compounds, nitrogen compounds, and nitrogen oxides generated by oxidation of nitrogen compounds Detects sulfur oxides or metal complexes of sulfur oxides, nitrogen compounds or metal complexes of nitrogen oxides, and aldehyde group concentrations and carboxyl group concentrations present in insulators, and detects the aldehyde groups. A fluid charging diagnostic method for an oil-filled electrical device, wherein the flow charge property of the oil-filled electrical device and a solid insulator therein is diagnosed using the concentration and the carboxyl group concentration as an index of fluid chargeability.

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