JP4948380B2 - Method for determination of sulfonic acid type sulfur content in insulating oil - Google Patents

Description

  The present invention relates to a method for determining a sulfonic acid type sulfur content in insulating oil.

  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 the winding that is 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.

  In an actual oil-filled electrical device, since it is difficult to stop, a test for measuring the degree of charge of insulating oil has been conducted as a method for grasping the flow chargeability without stopping. However, in such a test, the electrical insulating oil used as a sample requires a large amount of oil, the evaluation test itself requires a long time, and has a problem that it is easily influenced by the measurement environment. Furthermore, the insulation oil deteriorates and the degree of charge increases when used for a long time. In particular, as the aging of the transformer progresses, the quality of the insulation oil has deteriorated due to oxidation and thermal deterioration. As the degree of electrification increases, the fluid charging phenomenon is becoming apparent.

  As a countermeasure against such a fluid charging phenomenon, Patent Document 1 proposes to use a refined mineral oil having a resin content of 100 ppm or less in order to prevent deterioration of the insulating oil.

  Patent Document 2 reports a method of measuring the amount of sulfoxide contained in the electrical insulating oil and evaluating the deterioration state of the electrical insulating oil based on the amount of sulfoxide.

On the other hand, since the insulating oil used for oil-filled electrical equipment is a refined mineral oil, it contains 0.1 to 0.5% of a sulfur compound as a sulfur component. Patent Document 3 reports the relationship between the sulfur compound and the charge of oil, and according to this, when oil added with sulfides is heated, an oxidation product of sulfides is generated and the charge is increased. In the case of oils with added sulfoxides, which are oxidation products of sulfides, are more easily charged than sulfides; sulfones, which are oxidation products of sulfoxides, do not show a phenomenon of high charge in the heating test, etc. Has been reported.
JP 2000-345177 A JP 2001-006946 A JP-A-2005-223104

  As described above, the structure of sulfur compounds contained in insulating oil changes over time as the oil heats down, but the degree of charge is the sum of the charge amounts exhibited by each sulfur compound. The sulfur contained in the oil is the starting point, and the sulfur compound is oxidized to increase the degree of charge. When the oxidation further progresses, a sulfone that does not exhibit high charge and a sulfonic acid that exhibits reverse charge are generated. FIG. 1 shows the results of accelerated test results of octyl sulfur compounds in a system containing oxygen and a copper catalyst. The oil added with sulfide and sulfoxide is positively charged, and the oil added with sulfonic acid is Negatively charged.

  In actual oil-filled electrical equipment, it is known that when a newly installed oil-filled electrical equipment is in use, the charge of the insulating oil increases with the course of use. As a cause of this, sulfur-based trace components contained in insulating oil are assumed, and the total sulfur content in insulating oil can be quantified by coulometric titration, but each sulfur compound in insulating oil is quantitatively analyzed. There is no method, and the development of analytical methods is desired.

  The present invention has been made in view of the above circumstances, and makes it possible to easily and highly sensitively measure the sulfonic acid type sulfur content in the insulating oil of oil-filled electrical equipment, and the sulfonic acid in the insulating oil. It is an object of the present invention to provide a method for determining the type sulfur content.

  The present inventors diligently studied to solve the above problems. And, ethyl violet (Ethyl Violet) that is a cationic dye forms a stable blue conjugate with sulfonic acid-type sulfur under mildly acidic conditions, and this conjugate is dissolved in a nonpolar solvent. It has been found that even a trace amount of sulfonic acid type sulfur content in the insulating oil can be measured using a simple device, and the present invention has been achieved.

That is, the present invention is as follows.
(1) The insulating oil sample is brought into contact with an ethyl violet solution, water and a nonpolar solvent under weak acidity, and the sulfonic acid type sulfur content in the insulating oil is determined by colorimetrically comparing colors generated in the nonpolar solvent phase. A method for quantifying sulfonic acid type sulfur content in insulating oil, characterized by quantifying.
(2) The method for quantifying a sulfonic acid type sulfur content in an insulating oil according to the above (1), wherein the quantification is performed by colorimetric determination with a standard sample to which alkylbenzene or a new electric insulating oil is added.
(3) The method for determining a sulfonic acid type sulfur content in an insulating oil according to the above (1) or (2), wherein the colorimetry is performed by measuring the absorbance.
(4) The method for quantifying a sulfonic acid type sulfur content in an insulating oil as described in (2) or (3) above, wherein the standard sample is an alkyl sulfonic acid.
(5) The method for quantifying a sulfonic acid type sulfur content in insulating oil according to any one of (1) to (4), wherein the nonpolar solvent is toluene.

  According to the present invention, since the sulfonic acid type sulfur content in the insulating oil can be quantified at the ppm level without the need for special equipment or expensive measuring equipment, it can be easily performed in a short time with a small amount of oil. In addition, it is possible to evaluate the deterioration state of the insulating oil. In addition, by using the method of the present invention, it is possible to improve the accuracy of charge diagnosis of insulating oil, to elucidate the mechanism of the high charging phenomenon, and to suppress the high charging phenomenon based on the knowledge obtained thereby. Become.

  FIG. 2 is a flowchart showing a standard operation process of the quantification method of the present invention.

  As shown in FIG. 3, the sulfonic acid type sulfur content contained in the insulating oil starts from the sulfide contained in the new oil, and is generated via the sulfoxide produced by oxidation or from the sulfide. Presumed. Since the total carbon number of sulfides is in the range of 2-30, the carbon number of the sulfonic acid produced is estimated to be in the range of 1-15. This sulfonic acid type sulfur component exists in an ionized state in the insulating oil.

  Add an acetic acid buffer etc. to insulating oil containing sulfonic acid type sulfur, and react with ethyl violet under weak acidity, sulfonic acid in the insulating oil and ethyl violet react to form a stable blue conjugate To do. Since ethyl violet is a water-soluble dye, excess ethyl violet that has not reacted with the sulfonic acid exhibits a blue color in the aqueous phase, while the formed conjugate is insoluble in water and does not dissolve in water, It dissolves in a nonpolar solvent and exhibits a blue color in the solvent. Therefore, the conjugate can be directly measured using the blue color of the solvent as an index.

  Examples of the nonpolar solvent include benzene, toluene, xylene, hexane, cyclohexane, nonane, decane, undecane, dodecane, tridecane, and the like. Toluene is preferable from the viewpoint of good solubility and extractability of the conjugate.

  As the buffer kept under weak acidity, a solution in which anhydrous sodium sulfate, anhydrous sodium acetate and acetic acid are dissolved in water is preferable.

  In the present invention, weak acid conditions can be achieved by adding weak acid to the solution. The weak acid can be selected from those known in the art, but is preferably easily available and more inexpensive. Further, it is preferable to select in consideration of safety, and those that can be used in the form of a diluted aqueous solution are preferable. As the weak acid, acetic acid can be preferably used. When the ethyl violet solution is added into the slightly acidic mixture, a stable blue conjugate is formed. On the other hand, since the excess dye is water-soluble, water is added together with the nonpolar solvent, and the insulating oil sample, ethyl violet, water and the nonpolar solvent are sufficiently brought into contact with each other, the aqueous phase in which the excess dye is dissolved, and the conjugate Is separated from the dissolved solvent phase.

  In the method for determining the sulfonic acid type sulfur content of the present invention, since sulfonic acid is present in the insulating oil and there is almost no analysis interfering substance in the insulating oil, EDTA (ethylenediaminetetratetraacetic acid sodium ) And the like need not be added. In contrast, in the analysis of anionic surfactants contained in water such as tap water and factory effluent, ions such as Ca and Mg are present in the water, so that these ions do not interfere with the analysis. It is necessary to react with (form a complex).

  Since the conjugate dissolved in the nonpolar solvent exhibits a blue color, the sulfonic acid type sulfur content in the insulating oil can be quantified by comparing the colors generated in the nonpolar solvent phase. Colorimetry is preferably performed by measuring the absorbance around 635 nm. As the analyzer, an absorptiometer, a colorimeter or the like can be used.

  By comparing the color generated in the nonpolar solvent phase in the insulating oil sample with that of the standard sample, the sulfonic acid type sulfur content in the insulating oil sample can be quantified. As a standard sample, assuming a sulfonic acid generated from sulfide, an alkylsulfonic acid having 1 to 15 carbon atoms is suitable. Among them, octyl sulfonic acid is an octyl sulfide oxide that exhibits the highest degree of charge when investigating the relationship between the number of carbon atoms of the sulfide and the degree of charge. The compound having such a high degree of charge is used as an index. As a result, it becomes possible to accurately perform diagnosis and suppression measures for the phenomenon of increasing the degree of charging.

  Insulating oil containing a sulfonic acid type sulfur component has an absorption spectrum in the vicinity of 635 nm which is an absorbance measurement wavelength, and has a property of being dissolved in a nonpolar solvent. Therefore, when colorimetrically forming a non-polar solvent phase in a standard sample, the same amount of alkylbenzene or electrical insulating oil as that of the insulating oil sample is used together with the standard sample in order to eliminate the error in measuring the absorbance due to the influence of oil. It is better to add new oil. Alkylbenzene is a synthetic oil specified in JIS C 2320: 1999 “Electrical Insulating Oil”, and is preferably used because it does not contain a sulfur component (particularly sulfide). As an alternative to alkylbenzene, an electrical insulating oil (new oil) that does not undergo oxidative degradation can also be used. The type of alkylbenzene to be added may be either linear or branched, and varies depending on the type of insulating oil used as the sample. It is preferable to add a material having the same number of carbon atoms.

  When the quantification method of the present invention is applied to individual test samples or the like, special conditions, operations and the like are not required to be set. A measurement system related to the target substance of the present invention or a substance substantially equivalent thereto may be constructed by adding ordinary technical considerations to those skilled in the art to the normal conditions and operation methods in each method. For details of these general technical means, it is possible to refer to reviews, books and the like known in the analysis field.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited only to a following example.

(Preparation of reagents)
a. Ethyl violet solution 0.49 g of ethyl violet (for reagent / water quality test) was dissolved in 1 liter (L) of distilled water.
b. After 142 g of anhydrous Na sulfate was dissolved in 800 ml of acetic acid buffer distilled water, 27.2 g of anhydrous Na acetate and 12 ml of acetic acid were added. Distilled water was added to the obtained aqueous solution to make the whole 1 L.
c. Octylsulfonic acid standard solution About 20 mg of octylsulfonic acid (reagent) was dissolved in ethanol (reagent grade S), adjusted to 10 ml using ethanol, and an octylsulfonic acid ethanol solution having a concentration of about 2000 ppm was prepared.

(Calibration curve creation)
The octyl sulfonic acid standard solution prepared above was sampled using a micropipette at 0 μl, 10 μl, 20 μl, and 50 μl, and octyl sulfonic acid concentrations corresponding to 0 ppm, 2.4 ppm, 4.8 ppm, and 12.1 ppm, respectively. Prepared.

  In each of the obtained solutions, 3 ml of toluene, 1 ml of alkylbenzene <alkyl group (side chain) having 9 to 17 carbon atoms and 12,14 main components> (or fresh oil is acceptable), 0.5 ml Acetic acid buffer, 100 μl of ethyl violet solution and 5 ml of distilled water were added, and the mixture was placed in a 10 ml stoppered test tube, shaken well for about 10 seconds, and allowed to stand. When the aqueous phase and the toluene phase were separated after standing, the toluene phase was collected, and the absorbance at a wavelength of 635 nm was measured using a colorimeter (Unimeter UM1). The results are shown in Table 1.

  Since it was found that the absorbance increased in proportion to the sulfonic acid concentration, the sulfonic acid concentration and the absorbance value were plotted, and the relational expression between the sulfonic acid concentration (ppm) and the absorbance (μA) was obtained using these values. As a result, it was found that linearity was obtained.

(Quantification of sulfonic acid in sample oil)
1 ml of sample oil, 3 ml of toluene, 0.5 ml of acetate buffer, 100 μl of ethyl violet solution, and 5 ml of distilled water were added to a test tube with a stopper, and the mixture was shaken well for about 10 seconds, and then allowed to stand. When the aqueous phase and the toluene phase were separated after standing, the toluene phase was collected, and the absorbance at a wavelength of 635 nm was measured using a colorimeter (Unimeter UM1).

  The obtained absorbance measurement value was applied to the linear equation of FIG. 4 to quantify the sulfonic acid in the sample oil.

  Table 2 shows the results of testing using five types of insulating oil (samples Nos. 1 to 5).

  From the above results, it was confirmed that the sulfonic acid type sulfur content in the insulating oil could be determined using a simple absorptiometer.

  The above quantification method of sulfonic acid type sulfur in insulating oil enables the quantitative measurement of a small amount of sulfonic acid by simple operation and the use of inexpensive reagents, coupled with the fact that it can be quantified with a simple device. On the other hand, since it can measure sulfonic acid with high sensitivity while being quick and simple, it can be used as an index for grasping the flow charge of insulating oil of oil-filled electrical equipment.

  The present invention provides a simple and inexpensive method for quantifying sulfonic acid type sulfur content in insulating oil while having high sensitivity, and presents a high charging phenomenon that is currently a problem in oil-filled electrical equipment. Useful for diagnosis and suppression measures.

It is a graph which shows the acceleration test result (with oxygen and copper) of an octyl type | system | group sulfur compound. It is a flowchart which shows the standard operation process of the fixed_quantity | assay method of this invention. It is a figure which shows the molecular structure of the sulfur compound which exists in insulating oil. It is a graph which shows the calibration curve about octylsulfonic acid created using the quantitative method of this invention.

Claims (5)

  Quantifying the sulfonic acid type sulfur content in insulating oil by contacting an insulating oil sample with ethyl violet solution, water and a nonpolar solvent under weak acidity, and colorimetrically forming colors in the nonpolar solvent phase A method for determining a sulfonic acid type sulfur content in an insulating oil.   2. The method for quantifying a sulfonic acid type sulfur content in an insulating oil according to claim 1, wherein the quantification is performed by colorimetric determination with a standard sample to which alkylbenzene or a new electric insulating oil is added.   3. The method for quantifying a sulfonic acid type sulfur content in an insulating oil according to claim 1, wherein the colorimetry is carried out by absorbance measurement.   The method for quantifying a sulfonic acid type sulfur content in insulating oil according to claim 2 or 3, wherein the standard sample is an alkyl sulfonic acid.   The method for quantifying a sulfonic acid type sulfur content in an insulating oil according to any one of claims 1 to 4, wherein the nonpolar solvent is toluene.