METHOD FOR PREDICTING AMOUNT OF COPPER SULFATE PRODUCED IN OIL-FILLED ELECTRIC DERIVE, METHOD FOR DIAGNOSING OCCURRENCE OF ABNORMAL EVENT, METHOD FOR PREDICTING INITIAL CONCENTRATION OF DIBENZYL DISULFIDE IN INSULATING OIL, AND METHOD FOR DIAGNOSING POSSIBILITY OF OCCURRENCE OF ABNORMAL EVENT

Abstract

 Disclosed is a method for predicting the amount of copper sulfide produced in an oil-filled electric device, including the steps of: (1) measuring the concentration(s) of one or more specific product(s) contained in an insulating oil collected from the oil-filled electric device; and (2) predicting the production amount of copper sulfide on the basis of the concentration(s) of the specific product(s). The specific product(s) is/include at least one compound selected from the group consisting of benzyl alcohol, benzaldehyde, benzoic acid, and dibenzyl sulfoxide.

Description

TECHNICAL FIELD

[0001] This invention relates to a method for predicting the amount of copper sulfide produced in an oil-filled electric device such as a transformer, a method for diagnosing the occurrence of an abnormal event, a method for predicting the initial concentration of dibenzyl disulfide in an insulating oil, and a method for diagnosing a possibility of the occurrence of an abnormal event.

BACKGROUND ART

[0002] Generally, in an oil-filled electric device such as an oil-filled transformer, an insulating paper piece is wound around a copper coil, which is an electricity-passing medium, and further a structure is adopted which is made not to short-circuit adjacent turns of the copper coil between each other. In the oil-filled electric device, the copper coil and the insulating paper piece are set in an insulating oil taking charge of a cooling medium or some other.

[0003] Some insulating oils used in oil-filled electric devices contain a sulfur component. About this case, the following is known: the sulfur component in the insulating oils reacts with copper parts, whereby copper sulfide, which is electroconductive, precipitates on the insulating paper piece; thus, an electroconductive path is formed between adjacent turns of the coil, so that sulfidation corrosion, which causes dielectric breakdown, may be caused (for example, Non-Patent Literature 1: CIGRE TF A2. 31, "Copper sulphide in transformer insulation," ELECTRA, No. 224, pp. 20-23, 2006).

[0004] From such a viewpoint, attention has been paid to the selection of an insulating oil in which copper sulfide is not easily generated, and the development of a technique for restraining copper sulfide. However, about insulating oils used in oil-filled electric devices, the amount thereof is generally large and the number of years when the oils are used is also large; thus, the oils are not easily exchanged. Thus, for individual oil-filled electric devices in each of which an insulating oil containing a sulfur component is used, a method has been desired which is capable of predicting a possibility of the occurrence of an abnormal event, such as dielectric breakdown, caused by the precipitation of copper sulfide. If the possibility of the abnormal event is predicted, an appropriate measure or action can be taken in accordance with the state of each of the oil-filled electric devices.

[0005] As a substance for causing the precipitation of copper sulfide in an insulating oil, dibenzyl disulfide is known (for example, Non-Patent Literature 2: F. Scatiggio, V. Tumiatti, R. Maina, M. Tumiatti, M. Pompilli and R. Bartnikas, "Corrosive Sulfur in Insulating Oils: Its Detection and Correlated Power Apparatus Failures", IEEE Trans. Power Del., Vol. 23, pp. 508-509, 2008).

[0006] With reference to Fig. 5, a description is made about the mechanism that copper sulfide is generated from dibenzyl disulfide. As illustrated in Fig. 5, according to researches up to the present time, copper sulfide is generated through the following three-stage reactions (Non-Patent Literature 3: S. Toyama, J. Tanimura, N. Yamada, E. Nagao, T. Amimoto, "Highly Sensitive Detection Method of Dibenzyl Disulfide and Elucidation of Mechanism of Copper Sulfide Generation in Insulating Oil"), IEEE TDEI, Vol. 16, No. 2, p. 513 out of pp. 509-515, 2009):

"First stage": reaction wherein dibenzyl disulfide is coordinated (adsorbed) on a copper plate;

"Second stage": reaction wherein dibenzyl disulfide reacts with copper to produce a dibenzyl disulfide/Cu complex; and

"Third stage": reaction wherein the dibenzyl disulfide/Cu complex is subjected to thermal decomposition or some other to decompose into copper sulfide, and benzyl radicals and benzyl sulfenyl radicals.

[0007] Accordingly, by the production of copper sulfide, dibenzyl disulfide is consumed in the insulating oil while benzyl radicals and benzyl sulfenyl radicals are produced therein. The benzyl radicals and the benzyl sulfenyl radicals generate, as byproducts, bibenzyl, dibenzyl sulfide and dibenzyl disulfide in accordance with reaction between the radicals of the same species or between two species of the radicals. It is therefore conceived that the measurement of the respective production amounts (concentrations) of these byproducts makes it possible to give data on the production amount of copper sulfide.

[0008] However, it has been found out that when an insulating oil is under an air atmosphere (or an atmosphere which contains oxygen) in an oil-filled electric device such as an open type transformer, there is a case where copper sulfide is hardly produced. Such a case has the following problem: the respective production amounts of the above-mentioned byproducts (bibenzyl, dibenzyl sulfide, and dibenzyl disulfide) do not show any correlation with the production amount of copper sulfide; thus, even when the production amounts of the byproducts are measured, no information can be gained about the production amount of copper sulfide.

CITATION LIST

NON PATENT LITERATURE

[0009] 

NPL 1: CIGRE TF A2. 31, "Copper sulphide in transformer insulation," ELECTRA, No. 224, pp. 20-23, 2006

NPL 2: F. Scatiggio, V. Tumiatti, R. Maina, M. Tumiatti, M. Pompilli and R. Bartnikas, "Corrosive Sulfur in Insulating Oils: Its Detection and Correlated Power Apparatus Failures", IEEE Trans. Power Del., Vol. 23, pp. 508-509, 2008

NPL 3: S. Toyama, J. Tanimura, N. Yamada, E. Nagao, T. Amimoto, "Highly Sensitive Detection Method of Dibenzyl Disulfide and Elucidation of Mechanism of Copper Sulfide Generation in Insulating Oil"), IEEE TDEI, Vol. 16, No. 2, pp. 509-515, 2009

SUMMARY OF INVENTION

TECHNICAL PROBLEM

[0010] An object of the invention is to provide a method about which even when an insulating oil in an oil-filled electric device is under an atmosphere which contains oxygen, component(s) in the insulating oil is/are analyzed, thereby making it possible to predict, with high precision, the production amount of copper sulfide, and predict, with high precision, a possibility of the occurrence of an abnormal event (sulfidation corrosion) in the oil-filled electric device.

SOLUTION TO PROBLEM

[0011] In light of the above-mentioned problems, the inventors have made eager researches to find out that under an atmosphere which contains oxygen, benzyl radicals are changed to benzyl peroxide radicals, and then the radicals are further changed to benzyl alcohol, benzaldehyde or benzoic acid. Moreover, it has been found out that under an atmosphere which contains oxygen, benzyl sulfenyl radicals are changed to dibenzyl sulfoxide. The inventors have found out that analyses including ones of these final products are made, thereby making it possible that even when an insulating oil in an oil-filled electric device is under an atmosphere which contains oxygen, the production amount of copper sulfide is predicted with high precision. Thus, the invention has been achieved.

[0012] Accordingly, the invention is a method for predicting the amount of copper sulfide produced in an oil-filled electric device, including the steps of:

(1) measuring the concentration(s) of one or more specific product(s) contained in an insulating oil collected from the oil-filled electric device; and

(2) predicting the production amount of copper sulfide on the basis of the concentration(s) of the specific product(s); wherein

the specific product(s) is/include at least one compound selected from the group consisting of benzyl alcohol, benzaldehyde, benzoic acid, and dibenzyl sulfoxide.

[0013] Preferably, the specific products further include bibenzyl and/or dibenzyl sulfide.

[0014] The step (2) preferably includes the steps of:

converting the concentration of each of the specific products to the molar concentration of benzene rings, and then calculating a total molar concentration as the summation of the resultant molar concentrations; and

predicting the production amount of copper sulfide on the basis of the total molar concentration.

[0015] Furthermore, the invention also relates to a method for diagnosing the occurrence of an abnormal event in an oil-filled electric device on the basis of the production amount of copper sulfide that is predicted by use of the above-mentioned method.

[0016] The invention also relates to a method for predicting the initial concentration of dibenzyl disulfide in an insulating oil in an oil-filled electric device, including the steps of:

(1) measuring the concentration(s) of one or more specific product(s) collected from the oil-filled electric device; and

(2) predicting the initial concentration of dibenzyl disulfide on the basis of the concentration(s) of the specific product(s); wherein

the specific products include not only at least one compound selected from the group consisting of benzyl alcohol, benzaldehyde, benzoic acid, and dibenzyl sulfoxide, but also bibenzyl and/or dibenzyl sulfide; and
the step (2) includes the steps of:

converting the concentration of each of the specific products to the molar concentration of benzene rings, and then calculating a total molar concentration as the summation of the resultant molar concentrations;

calculating, from the total molar concentration, the reduced amount of dibenzyl disulfide, using a calibration curve prepared in advance; and

calculating the initial concentration of dibenzyl disulfide from the concentration of dibenzyl disulfide and the reduced amount of dibenzyl disulfide.

[0017] Additionally, the invention also relates to a method for diagnosing a possibility of the occurrence of an abnormal event in an oil-filled electric device on the basis of the initial concentration of dibenzyl disulfide predicted by use of the above-mentioned method.

ADVANTAGEOUS EFFECTS OF INVENTION

[0018] In the invention, measurement is made about the concentration(s) of specific product(s) being/including at least one compound selected from the group consisting of benzyl alcohol, benzaldehyde, benzoic acid, and dibenzyl sulfoxide in an insulating oil, thereby making it possible to predict the production amount of copper sulfide with high precision even when the insulating oil in an oil-filled electric device is under an atmosphere which contains oxygen. Thus, the occurrence of an abnormal event (sulfidation corrosion) in the oil-filled electric device can be diagnosed with high precision.

[0019] In the invention, measurement may be made about the respective concentrations of specific products including not only the one or more compounds selected from the group consisting of benzyl alcohol, benzaldehyde, benzoic acid, and dibenzyl sulfoxide but also bibenzyl and/or dibenzyl sulfide, thereby making it possible to predict the production amount of copper sulfide regardless of the type of the oil-filled electric device in each of a case where the insulating oil is under an atmosphere which contains oxygen and a case where the insulating oil is under an atmosphere which contains no oxygen. Thus, the occurrence of an abnormal event (sulfidation corrosion) in the oil-filled electric device can be diagnosed with high precision.

[0020] By predicting the initial concentration of a copper-sulfide-causative substance (dibenzyl disulfide) when the insulating oil is not yet used, a possibility of the occurrence of an abnormal event (sulfidation corrosion) in the oil-filled electric device can be diagnosed on the basis of the predicted concentration.

BRIEF DESCRIPTION OF DRAWINGS

[0021] 

Fig. 1 is a graph showing a relationship between the production amount of bibenzyl and that of copper sulfide under an air atmosphere, and a relationship between the production amount of benzaldehyde and that of copper sulfide under an air atmosphere.

Fig. 2 is a graph showing a relationship between the production amount of bibenzyl and that of copper sulfide under a nitrogen atmosphere.

Fig. 3 is a graph showing a relationship between the total molar concentration (N) of specific products and the production amount of copper sulfide under each of an air atmosphere and a nitrogen atmosphere.

Fig. 4 is a graph showing a relationship between the total molar concentration (N) of the specific products and the reduced amount of dibenzyl disulfide under each of an air atmosphere and a nitrogen atmosphere.

Fig. 5 is a schematic view illustrating the mechanism that copper sulfide is generated from dibenzyl disulfide.

DESCRIPTION OF EMBODIMENTS

(Embodiment 1)

<Prediction of the production amount of copper sulfide>

[0022] In the present embodiment,

(1) measurement is made about the concentration of only one compound selected from the group consisting of benzyl alcohol, benzaldehyde, benzoic acid, and dibenzyl sulfoxide as one or more specific product(s) contained in an insulating oil collected from an oil-filled electric device, and

(2) the amount of copper sulfide produced in the oil-filled electric device is predicted on the basis of the concentration of the specific product.

(1) Measurement of the concentration(s) of the specific product(s):

[0023] The concentration(s) of the specific product(s) contained in the insulating oil may be measured by use of various known methods, for example, by use of a gas chromatograph/mass spectrometer (GC/MS).

(2) Predicting the production amount of copper sulfide:

[0024] The method for predicting the production amount of copper sulfide in the oil-filled electric device on the basis of the concentration(s) of the specific product(s) may be a method of preparing, in advance, a calibration curve showing a correlative relationship between the concentration(s) of the specific product(s) and the production amount of copper sulfide. This calibration curve may be prepared, for example, by filling a model of the oil-filled electric device with an insulating oil wherein the initial concentration(s) of the specific product(s) and the initial concentration of copper sulfide have already been known, and then measuring the increased concentration(s) of the specific product(s) and the increased concentration of copper sulfide under predetermined individual conditions.

<Diagnosis of the occurrence of an abnormal event>

[0025] Furthermore, when the copper sulfide production amount predicted in the embodiment is compared with a specific standard value (threshold value), the occurrence of an abnormal event can be diagnosed in the oil-filled electric device.

[0026] The threshold value of the copper sulfide production amount is varied in accordance with the type and the structure of the oil-filled electric device. For example, when its insulating member has a sufficient thickness, the threshold value of the copper sulfide production amount becomes large. When the insulating member has a small thickness, the threshold value becomes small.

[0027] When the concentration of any one of the specific product(s) is equal to or more than this specific standard value (threshold value), the oil-filled electric device is diagnosed with an inconvenience (abnormal event) caused by the precipitation of copper sulfide. About a transformer diagnosed with an abnormal event, attention can be called to the person concerned in order that the person can preferentially take a necessary measure.

(Embodiment 2)

<Prediction of the production amount of copper sulfide>

[0028] In the present embodiment,

(1) measurement is made about the respective concentrations of not only at least one compound selected from the group consisting of benzyl alcohol, benzaldehyde, benzoic acid, and dibenzyl sulfoxide but also bibenzyl and/or dibenzyl sulfide as one or more specific product(s) contained in an insulating oil collected from an oil-filled electric device, and

(2) the amount of copper sulfide produced in the oil-filled electric device is predicted on the basis of the respective concentrations of the specific products.

(1) Measurement of the respective concentrations of the specific products:

[0029] The respective concentrations of the specific products contained in the insulating oil may be measured by use of various known methods, for example, by use of a gas chromatograph/mass spectrometer (GC/MS).

(2) Predicting the production amount of copper sulfide:

[0030] In the embodiment, the specific products contained in the insulating oil are measured, and then the concentration of each of the components is converted to the molar concentration of benzene rings. On the basis of a total molar concentration (N) as the summation of these molar concentrations, the production amount of copper sulfide is predicted. Specifically, the total molar concentration (N) is calculated from the respective concentrations of the components by use of the following equation (1):

[0031] In the equation (1), n1 represents the concentration (µmol/g) of benzyl alcohol in the oil; n2, that of benzaldehyde therein; n3, that of benzoic acid therein; n4, that of dibenzyl sulfoxide therein; n5, that of bibenzyl therein; and n6, that of dibenzyl sulfide therein.

[0032] The method for predicting the production amount of copper sulfide in the oil-filled electric device on the basis of the total molar concentration (N) may be a method of preparing, in advance, a calibration curve showing a correlative relationship between the total molar concentration (N) and the production amount of copper sulfide. This calibration curve may be prepared, for example, by filling a model of the oil-filled electric device with an insulating oil wherein the respective initial concentrations of the specific products and the initial concentration of copper sulfide have already been known, and then measuring the increased concentrations of the specific products and the increased concentration of copper sulfide under predetermined individual conditions.

[0033] About any actual transformer, it is known that the concentration of oxygen in an insulating oil in the transformer is varied from 100 to 30000 ppm (v/v) in accordance with the specification of the transformer and the driving situation of the transformer. In the embodiment, the production amount of copper sulfide can be predicted without being affected by the concentration of oxygen in the atmosphere for the insulating oil (or in the insulating oil). Thus, the embodiment is suitable for measuring an oil-filled electric device which contains an insulating oil that can have various oxygen concentrations.

<Diagnosis of the occurrence of an abnormal event>

[0034] Furthermore, when the copper sulfide production amount predicted in the embodiment is compared with a specific standard value (threshold value) in the same way as in embodiment 1, the occurrence of an abnormal event can be diagnosed in the oil-filled electric device.

[0035] In the same manner as in embodiment 1, about a transformer diagnosed with an abnormal event, attention can be called to the person concerned in order that the person can preferentially take a necessary measure.

(Embodiment 3)

<Prediction of the initial concentration of dibenzyl disulfide>

[0036] In the present embodiment,

(1) measurement is made about the concentration of each of the same specific products as in embodiment 2 as one or more specific product(s) contained in an insulating oil collected from an oil-filled electric device, and further measurement is made about the concentration of dibenzyl disulfide (abbreviated to DBDS hereinafter), and

(2) on the basis of the respective concentrations of the specific products, and the concentration of DBDS, the initial concentration of DBDS in the insulating oil in the oil-filled electric device is predicted.

[0037] The initial concentration of DBDS is important as an index for diagnosing a possibility of the occurrence of an abnormal event.

(1) Measurement of the concentrations of the specific products and DBDS:

[0038] The respective concentrations of the specific products contained in the insulating oil may be measured by use of various known methods, for example, by use of a gas chromatograph/mass spectrometer (GC/MS).

[0039] The method for measuring the (remaining) concentration of DBDS in the collected insulating oil may be a known method that may be of various types, for example, a method of analyzing the concentration by use of a gas chromatograph (see, for example, S. Toyama, J. Tanimura, N. Yamada, E. Nagao and T. Amimoto, "High sensitive detection method of dibenzyl disulfide and the elucidation of the mechanism of copper sulfide generation in insulating oil"), Doble Client Conf., Boston, MA, USA, Paper IM-8A, 2008).

(2) Prediction of the initial concentration of DBDS:

[0040] A method for predicting the initial concentration of DBDS in the present embodiment includes the steps of:

converting the concentration of each of the specific products to the molar concentration of benzene rings, and then calculating a total molar concentration (N) as the summation of the resultant molar concentrations;

calculating, from the total molar concentration (N), the reduced amount of dibenzyl disulfide, using a calibration curve prepared in advance; and

calculating the initial concentration of DBDS from the concentration of DBDS and the reduced amount of DBDS.

[0041] In the embodiment, therefore, a calibration curve is prepared in advance, which shows a correlative relationship between the total molar concentration (N) of the specific products and the reduced amount of DBDS. This calibration curve may be prepared, for example, by filling a model of the oil-filled electric device with an insulating oil containing DBDS having an already-known initial concentration, and then gaining the total molar concentration (N) of the specific products and the reduced amount of DBDS under predetermined conditions.

[0042] In the same way as in embodiment 2, the equation (1) is used to calculate out, from the respective concentrations of the specific products, the total molar concentration (N) of the molar concentrations of benzene rings, and then the calibration curve is used to calculate the reduced amount of DBDS from the calculated total molar concentration (N).

[0043] The initial concentration of DBDS is calculated out from the following equation (2):

[0044] About DBDS, which is a copper-sulfide-causative substance, the amount thereof is reduced by the generation of copper sulfide. Thus, it is not concluded that even when DBDS is not contained in an insulating oil collected from an oil-filled electric device that has passed through many years from the start of the operation thereof, the transformer is safe against any trouble based on copper sulfide. It can be stated that the production amount of copper sulfide in the transformer depends on the concentration of DBDS. Thus, when a risk based on copper sulfide is estimated, it is important to predict the initial concentration of DBDS in the oil-filled electric device at the start of the operation thereof.

<Diagnosis of a possibility of the occurrence of an abnormal event>

[0045] The initial concentration of DBDS predicted as described above is compared with a specific standard value (threshold value), thereby making it possible to diagnose a possibility of the occurrence of an abnormal event in the oil-filled electric device.

[0046] The threshold value of the initial concentration of DBDS may be determined in a test that has widely been used as a test for corrosive sulfur in an insulating oil. A test that is frequently used as such a test is JIS C 2101-17 (Corrosive Sulfur Test) in Japan or ASTM D 1275B in foreign countries. ASTM is an abbreviation of "American Society for Testing and Materials".

[0047] For example, JIS C 2101-17 can be used to make it possible to determine the threshold value in accordance with the following process: First, prepared is an insulating oil showing no corrosiveness according to JIS C 2101-17. Preferred examples of this insulating oil include sulfur-free synthetic oils, such as alkylbenzene and α-olefin. DBDS is dissolved in this insulating oil in a predetermined amount (for example, each of 50, 100, 150 and 200 ppm). In this way, each sample oil is prepared. The thus-prepared sample oils are used to make a test in accordance with a method described in JIS C 2101-17.2 to 17.5, and then the corrosiveness thereof is determined in accordance with a method described in JIS C 2101-17.6. When the results thereof demonstrate, for example, that the sample oils wherein the DBDS concentrations are 50 and 100 ppm, respectively, show no corrosiveness while the sample oils wherein the DBDS concentrations are 150 and 200 ppm, respectively, show corrosiveness, the value of 100 ppm, which is the upper limit of the range in which no corrosiveness is shown, can be defined as the threshold value.

[0048] When the initial concentration of DBDS is equal to or more than the specific standard value (threshold value), the oil-filled electric device is diagnosed as having a possibility that an inconvenience (abnormal event) is caused by the precipitation of copper sulfide therein. About a transformer diagnosed as having a possibility of the occurrence of an abnormal event, attention can be called to the person concerned in order that the person can preferentially take a necessary measure. As a result, the person can systematically cope with the abnormal event.

EXAMPLES

[0049] Hereinafter, the invention will be described in more detail by way of examples; however, the invention is not limited by these examples.

(Example 1)

[0050] First, prepared was a transformer oil (insulating oil) about which it was verified that no corrosive sulfur was contained therein according to ASTM D 1275B. Next, DBDS was added to this transformer oil to give a concentration of 300 ppm. Into a bottle having an internal volume of 10 cc were put and filled 4 g of this transformer oil and a copper plate, and then the bottle was stopped up with a rubber stopper. Thereafter, the bottle was heated at 165°C for respective predetermined periods (1, 2, 3, 5, 7, and 9 hours). A stainless steel tube having an internal diameter of several millimeters was caused to penetrate through the rubber stopper, thereby making it possible to bring the oil freely into contact with the air.

[0051] A gas chromatograph/mass spectrometer (GC/MS) was used to measure the respective concentrations of benzaldehyde and bibenzyl contained in the transformer oil after the oil was heated for the respective given periods.

[0052] In Fig. 1 is shown a relationship between the concentrations of the byproducts (benzaldehyde and bibenzyl) at the respective predetermined times, and the production amount of copper sulfide. The production amount of copper sulfide shows the rate of a change in the weight of the copper plate.

[0053] As illustrated in Fig. 1, a good correlation exists between the benzaldehyde amount and the production amount of copper sulfide. Thus, when the benzaldehyde amount is obtained, the production amount of copper sulfide at the temperature can be obtained. However, bibenzyl is hardly produced under an air atmosphere (oxygen-containing atmosphere) so that no correlation is shown between the amount thereof and the production amount of copper sulfide.

[0054] For comparison, in Fig. 2 are shown results obtained by making the same test under a nitrogen atmosphere. About the production amount of copper sulfide, shown is the value obtained by dividing a change in the weight of the copper plate per gram of the oil by the molecular weight of sulfur. As shown in Fig. 2, a good correlation is recognized between the production amount of bibenzyl and the production amount of copper sulfide under the nitrogen atmosphere (oxygen-free atmosphere).

[0055] From the results shown in Fig. 1, it is understood that in an air atmosphere (oxygen-containing atmosphere) also, the production amount of copper sulfide in an oil-filled electric device can be predicted by use of the concentration of benzaldehyde as an index. Such a relationship is obtained also about benzyl alcohol, dibenzyl sulfoxide, and benzoic acid. Thus, it is understood that when the amounts of these compounds are determined, the production amount of copper sulfide can be obtained.

[0056] In order to predict the production amount of copper sulfide, it is necessary to decide the temperature condition of the atmosphere wherein the oil-filled electric device is set, and the operation time thereof. These can be decided from the driving record of the oil-filled electric device, a fluctuation in the temperature of the environment, and others.

(Example 2)

[0057] The same experiment as in Example 1 was made to measure not only the respective concentrations of benzoic acid, benzyl alcohol, benzaldehyde, and dibenzyl sulfoxide contained in the transformer oil after the oil was heated but also those of bibenzyl and dibenzyl sulfide contained therein by use of a gas chromatograph/mass spectrometer (GC/MS). These concentrations were substituted for the respective variables in the equation (1) to calculate the total molar concentration (N).

[0058] Substantially the same experiment was made in a nitrogen atmosphere.

[0059] In the present example, in Fig. 3 is shown a relationship between the total molar concentration (N) obtained when the oil-filled electric device was heated for the predetermined periods under each of the air atmosphere and the nitrogen atmosphere, and the production amount of copper sulfide. About the production amount of copper sulfide, shown is the value obtained by dividing a change in the weight of the copper plate per gram of the oil by the molecular weight of sulfur. As shown in Fig. 3, a good correlation exists between the value N and the amount of copper sulfide. Thus, when the value N is obtained, the production amount of copper sulfide at the temperature can be predicted.

[0060] As is evident from Fig. 3, the results under the air atmosphere and those under the nitrogen atmosphere show substantially the same linear relationship. Thus, it is understood that the use of the value N as an index makes it possible to predict the production amount of copper sulfide regardless of the concentration of oxygen in any insulating oil. This matter demonstrates that a method as described in embodiment 2 makes it possible to predict the production amount of copper sulfide regardless of the type of the transformer (the transformer of an open type or of a close type).

(Example 3)

[0061] Substantially the same experiment as in Example 2 was made to obtain the value N in the same manner as in embodiment 2, and further measure the concentration of DBDS in the insulating oil at the respective predetermined heating times by use of a gas chromatograph/mass spectrometer (GC/MS). From the addition concentration (300 ppm) of DBDS, the reduced amount (µmol/g) of DBDS was calculated out. In Fig. 4 is shown a relationship between the resultant value N and the reduced amount of DBDS.

[0062] As shown in Fig. 4, a good correlation is shown between the value N and the reduced amount of DBDS. From this matter, it is understood that when an insulating oil collected from an oil-filled electric device that is being operated is analyzed to obtain the value N, the reduced amount of DBDS can be predicted, and further the initial concentration of DBDS can be calculated out from the equation (2).

[0063] As is evident from Fig. 4, the results in the air and those in nitrogen show substantially the same linear relationship. Thus, it is understood that the use of the value N as an index makes it possible to predict the initial concentration of DBDS regardless of the concentration of oxygen in any insulating oil. This matter demonstrates that a method as described in embodiment 3 makes it possible to predict the initial amount of DBDS regardless of the type of the transformer (the transformer of an open type or of a close type).

[0064] The above has described this invention in detail; however, this description is merely for exemplification, and does not limit the invention. It would be clearly understood that the scope of the invention is interpreted through the attached claims.

Claims

1. A method for predicting the amount of copper sulfide produced in an oil-filled electric device, comprising the steps of:

(1) measuring the concentration(s) of one or more specific product(s) contained in an insulating oil collected from said oil-filled electric device; and

(2) predicting said production amount of copper sulfide on the basis of the concentration(s) of said specific product(s); wherein

said specific product(s) is/comprise at least one compound selected from the group consisting of benzyl alcohol, benzaldehyde, benzoic acid, and dibenzyl sulfoxide.

2. The method according to claim 1, wherein said specific products further comprise bibenzyl and/or dibenzyl sulfide.

3. The method according to claim 2, wherein said step (2) comprises the steps of:

converting the concentration of each of said specific products to the molar concentration of benzene rings, and then calculating a total molar concentration as the summation of the resultant molar concentrations; and

predicting said production amount of copper sulfide on the basis of said total molar concentration.

4. A method for diagnosing the occurrence of an abnormal event in an oil-filled electric device on the basis of said production amount of copper sulfide that is predicted by use of the method recited in claim 1.

5. A method for predicting the initial concentration of dibenzyl disulfide in an insulating oil in an oil-filled electric device, comprising the steps of:

(1) measuring the concentration(s) of one or more specific product(s) collected from said oil-filled electric device; and

(2) predicting said initial concentration of dibenzyl disulfide on the basis of the concentration(s) of said specific product(s); wherein

said specific products comprise not only at least one compound selected from the group consisting of benzyl alcohol, benzaldehyde, benzoic acid, and dibenzyl sulfoxide, but also bibenzyl and/or dibenzyl sulfide; and
said step (2) comprises the steps of:

converting the concentration of each of said specific products to the molar concentration of benzene rings, and then calculating a total molar concentration as the summation of the resultant molar concentrations;

calculating, from the total molar concentration, the reduced amount of dibenzyl disulfide, using a calibration curve prepared in advance; and

calculating said initial concentration of dibenzyl disulfide from said concentration of dibenzyl disulfide and said reduced amount of dibenzyl disulfide.

6. A method for diagnosing a possibility of the occurrence of an abnormal event in an oil-filled electric device on the basis of said initial concentration of dibenzyl disulfide predicted by use of the method recited in claim 5.

Drawing