CN115128192B - Method for measuring Ostwald coefficient of dissolved gas in alkylbenzene insulating oil - Google Patents
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- 150000004996 alkyl benzenes Chemical class 0.000 title claims abstract description 95
- 238000000034 method Methods 0.000 title claims abstract description 89
- 239000012071 phase Substances 0.000 claims abstract description 28
- 229910052500 inorganic mineral Inorganic materials 0.000 claims abstract description 27
- 239000011707 mineral Substances 0.000 claims abstract description 27
- 239000007788 liquid Substances 0.000 claims abstract description 25
- 239000007791 liquid phase Substances 0.000 claims abstract description 24
- 238000007872 degassing Methods 0.000 claims abstract description 10
- 238000007599 discharging Methods 0.000 claims abstract description 9
- 239000007789 gas Substances 0.000 claims description 239
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 20
- 229910052757 nitrogen Inorganic materials 0.000 claims description 10
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 8
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 8
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 4
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 claims description 4
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 claims description 4
- 239000005977 Ethylene Substances 0.000 claims description 4
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 claims description 4
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 4
- 239000001569 carbon dioxide Substances 0.000 claims description 4
- 229910002091 carbon monoxide Inorganic materials 0.000 claims description 4
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 claims description 4
- 239000001257 hydrogen Substances 0.000 claims description 4
- 229910052739 hydrogen Inorganic materials 0.000 claims description 4
- 125000004435 hydrogen atom Chemical class [H]* 0.000 claims description 4
- 230000001681 protective effect Effects 0.000 claims description 3
- 238000012360 testing method Methods 0.000 abstract description 40
- 238000004364 calculation method Methods 0.000 abstract description 6
- 239000003921 oil Substances 0.000 description 181
- 238000004090 dissolution Methods 0.000 description 14
- 239000011521 glass Substances 0.000 description 14
- 238000004458 analytical method Methods 0.000 description 9
- 238000001514 detection method Methods 0.000 description 7
- 238000005259 measurement Methods 0.000 description 7
- 238000010926 purge Methods 0.000 description 7
- 238000007789 sealing Methods 0.000 description 7
- 238000002347 injection Methods 0.000 description 6
- 239000007924 injection Substances 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 230000005587 bubbling Effects 0.000 description 4
- 238000012937 correction Methods 0.000 description 4
- 238000003745 diagnosis Methods 0.000 description 4
- 229920001971 elastomer Polymers 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 238000000691 measurement method Methods 0.000 description 4
- 150000001335 aliphatic alkanes Chemical class 0.000 description 3
- 150000004945 aromatic hydrocarbons Chemical class 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- ZUOUZKKEUPVFJK-UHFFFAOYSA-N diphenyl Chemical compound C1=CC=CC=C1C1=CC=CC=C1 ZUOUZKKEUPVFJK-UHFFFAOYSA-N 0.000 description 2
- KWKXNDCHNDYVRT-UHFFFAOYSA-N dodecylbenzene Chemical compound CCCCCCCCCCCCC1=CC=CC=C1 KWKXNDCHNDYVRT-UHFFFAOYSA-N 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000000284 extract Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000002480 mineral oil Substances 0.000 description 2
- 235000010446 mineral oil Nutrition 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- LVZWSLJZHVFIQJ-UHFFFAOYSA-N Cyclopropane Chemical compound C1CC1 LVZWSLJZHVFIQJ-UHFFFAOYSA-N 0.000 description 1
- 241000588748 Klebsiella Species 0.000 description 1
- UFWIBTONFRDIAS-UHFFFAOYSA-N Naphthalene Chemical compound C1=CC=CC2=CC=CC=C21 UFWIBTONFRDIAS-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000004305 biphenyl Substances 0.000 description 1
- 235000010290 biphenyl Nutrition 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000004587 chromatography analysis Methods 0.000 description 1
- 150000001924 cycloalkanes Chemical class 0.000 description 1
- -1 cyclopropane Chemical class 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 238000004817 gas chromatography Methods 0.000 description 1
- 230000010358 mechanical oscillation Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000011002 quantification Methods 0.000 description 1
- 238000007430 reference method Methods 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000012289 standard assay Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/04—Preparation or injection of sample to be analysed
- G01N30/06—Preparation
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Abstract
The invention relates to a method for measuring the Ostwald coefficient of dissolved gas in alkylbenzene insulating oil, which comprises the steps of degassing the alkylbenzene insulating oil, introducing standard gas to ensure that the system reaches the first gas-liquid balance, and measuring the gas phase volume V g Volume of liquid phase V L Volume concentration C of characteristic gas g Optionally, when the Oswald coefficient of the characteristic gas in the mineral insulating oil is more than or equal to 0.5, the characteristic gas is obtained by calculation according to a formula (2), and when the Oswald coefficient of the characteristic gas in the mineral insulating oil is less than 0.5, the method further comprises the steps of discharging all the gas in a system, introducing standard gas to ensure that the system reaches the second gas-liquid balance, and testing and converting to obtain the gas phase volume V' g Volume V' of liquid phase L Volume concentration C 'of characteristic gas' g And (3) calculating according to a formula (3).
Description
Technical Field
The invention relates to the technical field of electric power, in particular to a method for measuring an Ostwald coefficient of dissolved gas in alkylbenzene insulating oil.
Background
Alkylbenzene synthetic insulating oil represented by Dodecylbenzene (DDB, dodelben) is widely used as an insulating medium in oil-filled cables, particularly ultrahigh-voltage submarine cables, because of its low viscosity, good gassing and high biodegradability.
When an overheat fault or an electrical fault occurs in the operation process of the submarine cable, the insulating oil can be decomposed, and the analysis and detection of the gas characteristics of the liquid insulating medium (insulating oil) in the electrical fault and the thermal fault are one of the most effective technical means for carrying out fault diagnosis and analysis of oil filling equipment. Therefore, the method for accurately measuring the content of the dissolved gas in the alkylbenzene insulating oil, grasping the gas production rule and the gas production characteristic has extremely important value for carrying out fault analysis and diagnosis of the oil-filled cable. However, at present, all characteristic gas testing methods of insulating oil are set based on insulating oil of natural mineral oil, and no method for measuring alkylbenzene synthetic insulating oil is reported.
The main components of the traditional insulating oil for electric power system are saturated alkane, cycloalkane such as cyclopropane, long-chain fatty alkane and the like, and also comprise a small amount of aromatic hydrocarbon such as biphenyl and the like, and the insulating oil is extracted from natural minerals. The main component of DDB is alkylbenzene, which has a great difference with the molecular structure of traditional mineral insulating oil, and shows completely different physical, chemical and electrical characteristics, so that the testing method suitable for mineral oil is not suitable for dodecylbenzene.
Therefore, it is desirable to provide a method for measuring the concentration of dissolved gas in an alkylbenzene insulating oil.
Disclosure of Invention
The invention aims to provide a method for measuring the Ostwald coefficient of dissolved gas in alkylbenzene insulating oil, which can be used for measuring the concentration of the dissolved gas in the alkylbenzene insulating oil. The alkylbenzene insulating oil can be used as submarine cable insulating oil, and potential safety hazards of submarine cables can be found by detecting characteristic gas of the submarine cable insulating oil.
The first aspect of the invention provides a method for measuring the ostwald coefficient of dissolved gas in alkylbenzene insulating oil, comprising the following measuring steps:
s100: providing a standard gas comprising a characteristic gas and a protective gas dissolved in an alkylbenzene insulating oil, the characteristic gas having a volume concentration of
S200: adding alkylbenzene insulating oil into a closed container, degassing the alkylbenzene insulating oil, introducing standard gas to ensure that the obtained system reaches the first gas-liquid balance, and measuring the gas phase volume V in the system g Volume of liquid phase V L And optionally, when the Ostwald coefficient of the characteristic gas in the mineral insulating oil is more than or equal to 0.5, calculating k according to a formula (2), namely the Ostwald coefficient;
the characteristic gas has an Oswald coefficient of less than 0.5 in mineral insulating oil, and further comprises the following steps:
s300: discharging all the gas in the closed container, introducing standard gas II to make the obtained system reach secondary gas-liquid balance, and heating at temperature T 1 The gas phase volume V 'of the system was measured as follows' g Volume of liquid phase V' L The volume concentration C 'of the characteristic gas' g The method comprises the steps of carrying out a first treatment on the surface of the The volume of the gas phase V' g Converted into temperature T 2 The volume V' of the gas phase below g The volume of the liquid phase V' L Converted into temperature T 2 The volume V' of the liquid phase L ；
S300: discharging all the gas in the closed container, introducing standard gas II to make the obtained system reach secondary gas-liquid balance, and heating at temperature T 1 The gas phase volume V 'of the system was measured as follows' g Volume of liquid phase V' L The volume concentration C 'of the characteristic gas' g The method comprises the steps of carrying out a first treatment on the surface of the The volume of the gas phase V' g Converted into temperature T 2 Lower gas phaseProduct V g The volume of the liquid phase V' L Converted into temperature T 2 Volume of liquid phase V' L ；
Calculating k' according to a formula (3), namely obtaining the Ostwald coefficient;
in some embodiments, in the method for measuring ostwald coefficient, in the step S100, the volume concentration of the characteristic gas5uL/L to 5000uL/L; and/or the number of the groups of groups,
the characteristic gas is selected from any one of hydrogen, carbon monoxide, carbon dioxide, methane, ethylene, ethane and acetylene; and/or the number of the groups of groups,
the volume ratio of the blank oil I obtained after degassing in the step S200 to the standard gas introduced in the step S300 is 1:1, a step of; and/or the number of the groups of groups,
the volume ratio of the blank oil II obtained after all the gases are discharged in the step S300 to the introduced standard gas is 1:1.
in some embodiments, in the method for determining the ostwald coefficient, when the characteristic gas is carbon dioxide, ethylene, ethane or acetylene, k is calculated according to formula (2), i.e. the ostwald coefficient
And when the characteristic gas is hydrogen, carbon monoxide or methane, calculating k' according to a formula (3), namely obtaining the Ostwald coefficient.
In some embodiments, in the method for determining the ostwald coefficient, in the step S200, a standard gas is introduced, and the system is continuously oscillated for 10-30 min in a constant temperature timing oscillator and then is stationary for 5-15 min, so that the obtained system reaches a first gas-liquid balance; and/or the number of the groups of groups,
adding alkylbenzene insulating oil into a closed container, bubbling and purging the alkylbenzene insulating oil for 2-4 hours by introducing high-purity nitrogen, and degassing the alkylbenzene insulating oil; and/or the number of the groups of groups,
introducing standard gas at temperature T 2 Under constant pressure, the resulting system reaches a first gas-liquid equilibrium.
In some embodiments, in the method for measuring ostwald coefficient, in the step S300, the temperature T 2 50 ℃; and/or the number of the groups of groups,
bubbling and purging high-purity nitrogen for 2-4 hours, and discharging all the gas in the closed container; and/or the number of the groups of groups,
introducing standard gas, continuously oscillating for 10-30 min in a constant temperature timing oscillator, and then standing for 5-15 min to ensure that the obtained system reaches secondary gas-liquid balance.
In some embodiments, in the method for determining the ostwald coefficient, the gas phase volume V 'is determined according to formula (4)' g Converted into temperature T 2 Volume of gas phase V 'below' g ；
The volume of the liquid phase V 'is determined according to formula (5)' L Converted into temperature T 2 Volume of liquid phase V' L ；
V″ L ＝V′ L ×[1+α×(T 2 -T 1 )] (5)；
Alpha is the thermal expansion coefficient of the alkylbenzene insulating oil.
In some embodiments, the method for determining the ostwald coefficient further comprises the following steps of determining the thermal expansion coefficient α of the alkylbenzene insulating oil: selecting a temperature point T with a temperature difference between 5 ℃ and 14 ℃ within a temperature range of 20 ℃ to 90 DEG C 3 And T 4 And T is 3 ＞T 4 The method comprises the steps of carrying out a first treatment on the surface of the Respectively measuring the temperature T 3 And said temperature T 4 The density ρ of the alkylbenzene insulating oil described below 1 And ρ 2 ；
Calculating alpha according to a formula (6);
the second aspect of the present invention provides a method for measuring the concentration of dissolved gas in an alkylbenzene insulating oil, comprising the steps of: adding alkylbenzene insulating oil into a closed container, introducing standard gas, obtaining a system with gas-liquid balance, and measuring the gas volume V in the system ig Volume of liquid V iL And the volume concentration C of the characteristic gas i ig The method comprises the steps of carrying out a first treatment on the surface of the The standard gas is as defined in the first aspect of the invention;
x is calculated according to the formula (1) i I.e. the concentration of the dissolved characteristic gas i in the alkylbenzene insulating oil;
wherein k is i Is the ostwald coefficient of the dissolved characteristic gas i in the alkylbenzene insulating oil, and is measured according to the measuring method provided in the first aspect of the present invention.
In some embodiments, in the method of determining the concentration, the concentration C of the characteristic gas i is determined by an external standard assay ig : detecting the peak area A of the characteristic gas i on an integrator by adopting a gas phase detector i Detecting peak area A of external standard characteristic gas i on integrator is And the concentration C of the external standard characteristic gas i is The method comprises the steps of carrying out a first treatment on the surface of the Calculating according to formula (7) to obtain the C ig ；
In a third aspect of the invention, there is provided an application of the concentration measurement method provided in the second aspect of the invention in fault detection of a deep sea insulated cable.
The traditional mineral insulating oil and the alkylbenzene insulating oil have completely different components and completely different physicochemical properties, so that the adsorption and dissolution capacities of the mineral insulating oil and the alkylbenzene insulating oil on characteristic gases are completely different, and therefore, the current method for measuring the dissolved gases of the mineral insulating oil is not suitable for the alkylbenzene insulating oil. The invention establishes the method for measuring the gas dissolution balance coefficient of the alkylbenzene insulating oil system, and selectively selects different measuring modes according to the difference of the estimated Oswald coefficient of the characteristic gas to be measured, thereby having strong pertinence, small error and high accuracy, and the measuring result has obvious difference with the gas dissolution balance coefficient of the mineral insulating oil body.
The insulating oil expands after being heated, and the thermal expansion characteristic value of the reactive insulating oil is the thermal expansion coefficient of the insulating oil. The volume of the insulating oil at 20 to 50 ℃ is converted when calculating the dissolution balance coefficient of the insulating oil. The detection method can detect the equilibrium constant of dissolved gas in the alkylbenzene insulating oil at 50 ℃.
Detailed Description
The invention is further illustrated below in conjunction with the embodiments and examples. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. Furthermore, it is to be understood that various changes and modifications may be made by one skilled in the art after reading the teachings of the invention, and such equivalents are intended to fall within the scope of the claims appended hereto.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Terminology
Unless otherwise indicated or contradicted, terms or phrases used herein have the following meanings:
the term "and/or," "and/or," as used herein, includes any one of two or more of the listed items in relation to each other, as well as any and all combinations of the listed items in relation to each other, including any two of the listed items in relation to each other, any more of the listed items in relation to each other, or all combinations of the listed items in relation to each other. It should be noted that, when at least three items are connected by at least two conjunctions selected from the group consisting of "and/or", "and/or", it should be understood that, in the present application, the technical solutions undoubtedly include technical solutions that are all connected by "logical and", and undoubtedly include technical solutions that are all connected by "logical or". For example, "a and/or B" includes three parallel schemes A, B and a+b. For another example, the technical schemes of "a, and/or B, and/or C, and/or D" include any one of A, B, C, D (i.e., the technical scheme of "logical or" connection), and also include any and all combinations of A, B, C, D, i.e., any two or three of A, B, C, D, and also include four combinations of A, B, C, D (i.e., the technical scheme of "logical and" connection).
Herein, "preferred", "better", etc. are merely embodiments or examples that describe better results, and it should be understood that they do not limit the scope of the invention.
In the present invention, "further", "still further", "particularly" and the like are used for descriptive purposes to indicate differences in content but should not be construed as limiting the scope of the invention.
In the present invention, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or quantity, nor as implying an importance or quantity of a technical feature being indicated. Moreover, "first," "second," "third," etc. are for non-exhaustive list description purposes only, and it should be understood that no closed limitation on the number is made.
In the invention, the technical characteristics described in an open mode comprise a closed technical scheme composed of the listed characteristics and also comprise an open technical scheme comprising the listed characteristics.
In the present invention, a numerical range (i.e., a numerical range) is referred to, and optional numerical distributions are considered to be continuous within the numerical range and include two numerical endpoints (i.e., a minimum value and a maximum value) of the numerical range and each numerical value between the two numerical endpoints unless otherwise specified. When a numerical range merely points to integers within the numerical range, both end integers of the numerical range are included, as well as each integer between the two ends, unless expressly stated otherwise. Further, when a plurality of range description features or characteristics are provided, these ranges may be combined. In other words, unless otherwise indicated, the ranges disclosed herein are to be understood to include any and all subranges subsumed therein.
The temperature parameter in the present invention is not particularly limited, and may be a constant temperature treatment or may vary within a predetermined temperature range. It should be appreciated that the constant temperature process described allows the temperature to fluctuate within the accuracy of the instrument control. Allows for fluctuations within a range such as + -0.5 ℃, + -0.4 ℃, + -0.3 ℃, + -0.2 ℃, + -0.1 ℃.
Herein, referring to a unit of data range, if a unit is only carried behind the right end point, the units indicating the left and right end points are the same. For example, 20 to 40 minutes means that the units of the left end point "20" and the right end point "40" are all minutes.
The main components of the traditional mineral insulating oil are alkane, naphthene and a small amount of aromatic hydrocarbon, the main components of the alkylbenzene insulating oil are aromatic hydrocarbon mainly composed of linear alkylbenzene, and the two are different in chemical composition and obvious in physical property difference, and can be seen from the performance comparison results of the alkylbenzene insulating oil 1 of a certain model, the alkylbenzene insulating oil 2 of a certain model and the mineral insulating oil in table 1.
TABLE 1 results of performance comparisons of alkylbenzene insulating oils and mineral insulating oils
| Project name | Alkylbenzene insulating oil 1 | Alkylbenzene insulating oil 2 | Mineral insulating oil |
| Appearance of | Colorless and transparent | Colorless and transparent | Colorless and transparent |
| Density (20 ℃ C.)/(g.cm) -3 ) | 0.859 | 0.858 | 0.895 |
| Kinematic viscosity (40 ℃ C.)/(mm 2. S) -1 ) | 3.53 | 4.26 | 8.5 |
| Flash point (closed)/DEGC | 146.5 | 150 | 140 |
| Pour point/. Degree.C | -60 | -60 | -25 |
| Acid value/(mgKOH.g) -1 ) | 0.0168 | 0.003 | 0.001 |
| Dielectric loss tan delta x 10 -4 | 3.8 | 7.1 | 3 |
| Volume resistivity (Ω. M) | 6.71×10 12 | 1.53×10 13 | 1×10 13 |
| Breakdown voltage/(kV.2.5 mm) -1 ) | 73.6 | 77.4 | 60 |
In order to study the gas production characteristics of alkylbenzene insulating oil under faults, establish the alkylbenzene insulating oil gas diagnosis standard, the content of the dissolved fault gas in the alkylbenzene insulating oil needs to be accurately measured. The method is simple to operate and convenient to calculate, firstly, in a sealing system formed by an oil sample and an eluting gas under the constant temperature and constant pressure condition, the dissolved gas in the oil reaches distribution balance in gas and liquid phases in a vibration mode and the like, the concentration of the characteristic gas in the gas phase is detected, and then the concentration of each component of the dissolved gas in the oil can be calculated by using a dissolution balance coefficient according to the distribution law and the material balance principle.
However, the application range of the current chromatographic test method for the dissolved gas of the insulating oil is only mineral insulating oil, for example, in the standard DL/T722-2016 (rules for analysis and judgment of dissolved gas in transformer oil), and parameters used in the calculation of the content of the dissolved gas are all parameters of the mineral insulating oil. Because the physical and chemical properties of the alkyl benzene insulating oil and the mineral insulating oil are obviously different, the dissolution characteristics of the two insulating oils on the same fault gas may be different, and a large error exists in the chromatographic detection technology of directly applying the mineral insulating oil gas, it is necessary to establish the chromatographic detection technology of the dissolution gas suitable for the alkyl benzene, so that the real capability of the dissolution gas of the alkyl benzene can be reflected.
In the present invention, the solubility equilibrium coefficient and the ostwald coefficient have the same definition, and are used for measuring the solubility of a gas in insulating oil, and can be expressed by the following formula:
the first aspect of the invention provides a method for determining the ostwald coefficient of dissolved gas in alkylbenzene insulating oil, which can select a proper determination method for different gases to be tested, and further can accurately determine the concentration of the dissolved gas in the alkylbenzene insulating oil.
In some embodiments, the method for determining the ostwald coefficient of dissolved gas in alkylbenzene insulating oil comprises the following steps:
s100: providing a standard gas comprising a characteristic gas and a protective gas dissolved in an alkylbenzene insulating oil, the characteristic gas having a volume concentration of
S200: adding alkylbenzene insulating oil into a closed container, degassing the alkylbenzene insulating oil, introducing standard gas to make the obtained system reach first gas-liquid equilibrium, and measuring gas phase volume V in the system g Volume of liquid phase V L Volume concentration C of characteristic gas g ；
K is calculated according to the formula (2), namely the Ostwald coefficient;
in some embodiments, in step S100, the concentration of the feature gas5uL/L to 5000uL/L.
In some embodiments, in step S200, alkylbenzene insulating oil is added into a closed container, high-purity nitrogen is bubbled and purged for 2 to 4 hours, and the alkylbenzene insulating oil is degassed.
In some embodiments, in step S200, a standard gas is introduced at a temperature T 2 Under constant pressure, the resulting system reaches a first gas-liquid equilibrium. In some embodiments, temperature T 2 Is 50 ℃.
In some embodiments, in step S200, standard gas is introduced, and the system is continuously oscillated in a constant temperature timing oscillator for 10-30 min, and then is stationary for 5-15 min, so that the obtained system reaches the first gas-liquid balance.
In some embodiments, in step S200, the volume ratio of the blank oil i obtained after degassing to the standard gas introduced is 1:1.
in some embodiments, the method for determining the ostwald coefficient of a dissolved gas in an alkylbenzene insulating oil comprises the steps of: a certain volume of white oil and a certain volume of gas containing components to be measured are put into a closed container (such as a syringe), the gas and the liquid are balanced by technical means such as oscillation under a constant temperature and constant pressure environment (such as 50 ℃ and 101.3 kPa), the actual concentration and the concentration after balancing of a certain component i in a gas phase are measured, and the dissolved gas balance coefficient ki of the component i at the measurement temperature is obtained according to a balance coefficient definition and a material balance principle and a formula (2).
In some embodiments, the method for determining the ostwald coefficient of dissolved gas in alkylbenzene insulating oil includes step S100 and step S200, and further includes the following steps:
s300: discharging all the gas in the closed container, introducing standard gas II to make the obtained system reach secondary gas-liquid balance, and heating at temperature T 1 Lower measurementThe gas phase volume V 'of the system' g Volume of liquid phase V' L The volume concentration C 'of the characteristic gas' g The method comprises the steps of carrying out a first treatment on the surface of the Volume of gas phase V' g Converted into temperature T 2 The volume V' of the gas phase below g Volume of liquid phase V' L Converted into temperature T 2 The volume V' of the liquid phase L ；
Calculating k' according to a formula (3), namely obtaining the Ostwald coefficient;
in some embodiments, in step S300, high-purity nitrogen is introduced to bubble and purge for 2-4 hours, and all the gas of the closed system I is discharged.
In some embodiments, in step S300, the volume ratio of the blank oil ii obtained after discharging all the gas to the standard gas introduced is 1:1.
in some embodiments, in step S300, the temperature T 2 Is 50 ℃.
In some embodiments, in step S300, standard gas is introduced, and the system is continuously oscillated in a constant temperature timing oscillator for 10-30 min, and then is stationary for 5-15 min, so that the obtained system reaches the second gas-liquid balance.
In some embodiments, the gas phase volume V 'is calculated according to equation (4)' g Converted into temperature T 2 The volume V' of the gas phase below g ；
The insulating oil expands after being heated, and the thermal expansion characteristic value of the reactive insulating oil is the thermal expansion coefficient of the insulating oil. In the case where the volume value at 20 ℃ needs to be converted to 50 ℃ in the process of calculating the dissolution balance coefficient, the thermal expansion coefficient of the insulating oil is involved. According to the invention, the equilibrium coefficients of the alkylbenzene insulating oil are measured by a proper test mode, and the equilibrium coefficients of the components of the dissolved gas of the alkylbenzene insulating oil at 50 ℃ are calculated.
In some embodiments, the thermal expansion coefficient of the insulating oil may be determined according to DL/T1204-2013, mineral insulating oil thermal expansion coefficient determination method.
In some embodiments, in the range below 90 ℃, two temperature points with the temperature difference between 5 ℃ and 14 ℃ are selected, the density of the insulating oil at the two points is measured, and the measured density difference is divided by the product of the density and the temperature difference at the lower temperature to obtain the average thermal expansion coefficient, wherein the formula is as follows:
wherein: alpha is the thermal expansion coefficient of submarine cable oil and is 1/DEGC;
ρ 1 is density, g/cm of sea cable oil at lower temperature 3 ；
ρ 2 Is density, g/cm of sea cable oil at higher temperature 3 ；
Δt is the difference between the two temperature points, DEG C.
In some embodiments, the method for determining the ostwald coefficient further comprises the steps of determining the thermal expansion coefficient α of the alkylbenzene insulating oil: selecting a temperature point T with a temperature difference between 5 ℃ and 14 ℃ within a temperature range of 0 ℃ to 90 DEG C 3 And T 4 And T is 3 ＞T 4 The method comprises the steps of carrying out a first treatment on the surface of the Respectively measuring the temperature T 3 And said temperature T 4 The density ρ of the alkylbenzene insulating oil described below 1 And ρ 2 ；
Calculating alpha according to a formula (6);
in some embodiments, the liquid phase volume V 'is determined according to equation (5)' L Converted into temperature T 2 The volume V' of the liquid phase L ；
V L ″＝V′ L ×[1+α×(T 2 -T 1 )] (5)；
Alpha is the thermal expansion coefficient of the alkylbenzene insulating oil.
In some embodiments, the method for determining the ostwald coefficient of a dissolved gas in an alkylbenzene insulating oil comprises the steps of: placing a certain volume of blank oil and a certain volume of gas containing a certain component to be tested into a closed container, and measuring the concentration of the component in the gas after gas-liquid dissolution balance at constant temperature; then exhausting the gas, filling a certain volume of blank gas, balancing for the second time at the same constant temperature, and measuring the concentration of the component in the gas; the dissolved gas equilibrium coefficient ki of this component i at the measurement temperature is determined according to formula (3).
In some embodiments, the Ostwald coefficient of the characteristic gas is determined by selecting different measurement methods according to the Ostwald coefficient of the characteristic gas in the mineral insulating oil and the Ostwald coefficient of the characteristic gas in the alkylbenzene insulating oil. Preferably, when the Oswald coefficient in the characteristic gas mineral insulating oil is more than or equal to 0.5, selecting the formula (2) for calculation; when the Oswald coefficient in the characteristic gas mineral insulating oil is less than 0.5, the formula (3) is selected for calculation, and the formula (2) are selected for calculation according to the estimated value of the Oswald coefficient, so that the measurement error of the dissolved gas balance coefficient ki is further reduced, and the measurement is more accurate.
In some embodiments, equation (2) applies to gas components with a greater ostwald coefficient, reducing the relative volume of the gas phase at equilibrium, which is beneficial for improved measurement accuracy.
In some embodiments, equation (3) is suitable for determining gas components with smaller ostwald coefficients, increasing the relative volume of the gas phase at equilibrium, which is beneficial for improving the accuracy of the determination.
In some embodiments, the characteristic gas is carbon dioxide, ethylene, ethane or acetylene, and k is calculated according to formula (2), i.e. the ostwald coefficient;
in some embodiments, the characteristic gas is hydrogen, carbon monoxide or methane, and k' is calculated according to formula (3), i.e. the ostwald coefficient.
In some embodiments, the method for determining the ostwald coefficient of a dissolved gas in an alkylbenzene insulating oil comprises the steps of:
1) And (3) an external calibration method is adopted, and the gas chromatograph is required to be calibrated before the test. Opening a valve of a standard gas steel cylinder, purging residual gas in a pressure reducing valve, extracting 1mL of standard mixed gas for sample injection by using a 1mL glass injector D, and repeating the operation twice, wherein the repeatability of two adjacent calibrations is kept within 1.5% of the average value;
2) And (5) preparing the blank oil. Respectively taking 200-250 mL of test oil, putting the test oil into two special normal temperature and pressure saturators (one of which is parallel), and bubbling and purging the test oil for 2-4 hours at room temperature by high-purity nitrogen until other gas components in the oil are completely purged;
3) Preparing an air storage glass injector, namely taking a plurality of 5mL glass injectors A, sucking about 0.5mL of test oil after each glass injector A extracts a small amount of test oil from the inner wall of a syringe barrel for 1-2 times, sleeving a rubber sealing cap, inserting a double-head needle head, vertically upwards inserting the needle head, and slowly discharging air and test oil in the injector to ensure that the test oil is fully filled in the inner wall of the injector without residual air;
4) Connecting an outlet of a 100mL syringe B with an oil outlet, sucking test oil for rinsing, sucking 20mL of blank test oil, sealing the outlet of the syringe by using a rubber sealing cap, and avoiding air bubbles from entering the syringe as much as possible in the process of taking an oil sample;
5) Taking a 5mL glass injector C, connecting a dental 5-gauge needle, cleaning with mixed gas for 1-2 times, extracting about 5mL of standard mixed gas, slowly injecting the gas in the injector C into the injector B, keeping continuous bubbles discharged from the needle tip in oil during air filling, and repeatedly operating for 4 times to fill about 20mL of standard mixed gas;
6) Placing the injector B into a constant temperature timing oscillator, continuously oscillating for 20min, and then standing for 10min;
7) Taking out the injector B from the constant temperature timing oscillator, taking all balance gas in the injector B into the injector A through a double-ended needle head (the gas after the first balance does not need to record the volume of the gas), and extracting 1mL of gas from the injector A by using a 1mL glass injector D (the same gas is used in the step 1) for sample injection analysis;
8) Step 6 is repeated by filling 20mL of nitrogen into the injector B containing the oil sample after the first balancing similarly to the operation in the step 5;
9) Taking out the injector B from the constant temperature timing oscillator, taking all balance gas in the injector B into the injector A through a double-ended needle head, standing for 2min at room temperature, accurately reading and recording the gas volume to 0.1mL, and extracting 1mL of gas from the injector A by using a 1mL glass injector D (the same branch as that used in the step 1) for sample injection analysis;
10 Method a): repeating the steps 3 to 7 for three times for the same oil test to obtain three groups of data;
method B: and (3) repeating the steps 3 to 9 for three times for the same oil test to obtain three groups of data.
11 Method a and method B): repeating the steps 3 to 10 for the parallel sample;
12 Correcting and calculating the volume of the gas and the test oil after balancing at room temperature according to the formula (4) and the formula (5);
13 Reference methods A and B, and reference formulas (4) and (5) are used to calculate the dissolved gas equilibrium coefficient ki of each gas component at 50deg.C.
Second aspect of the invention
The second aspect of the invention provides a method for determining the concentration of dissolved gas in alkylbenzene insulating oil, which can accurately reflect the dissolution degree of gas in the alkylbenzene insulating oil, and has high repeatability and simple operation.
In some embodiments, the method for determining the concentration of dissolved gas in an alkylbenzene insulating oil comprises the steps of: adding alkylbenzene insulating oil into a closed container, introducing standard gas, obtaining a system with gas-liquid balance, and measuring the gas volume V in the system ig Volume of liquid V iL The volume concentration C of the characteristic gas i ig ；
X is calculated according to the formula (1) i Namely in alkylbenzene insulating oilThe concentration of dissolved characteristic gas i;
wherein k is i The ostwald coefficient of the dissolved characteristic gas i in the alkylbenzene insulating oil is measured according to the measuring method provided in the second aspect of the present invention.
In some embodiments, the concentration C of the characteristic gas i is determined by an external standard quantification method ig : detection of the peak area A of a characteristic gas i on an integrator by a gas phase detector i Detecting peak area A of external standard characteristic gas i on integrator is And the concentration C of the external standard characteristic gas i is The method comprises the steps of carrying out a first treatment on the surface of the C is calculated according to the formula (7) ig ；
In some embodiments, chromatographic analysis of the content of dissolved gas components in alkylbenzene insulating oil is performed with reference to GB/T17623 gas chromatography determination of the content of dissolved gas components in insulating oil.
In some embodiments, the temperature correction factor of the concentration of dissolved gas in the alkylbenzene insulating oil is calculated when the concentration of dissolved gas in the alkylbenzene insulating oil is converted from 50 ℃ to 20 ℃. The derivation process of the correction coefficient is as follows:
from Klebsiella Long Fangcheng dp/dT=L/(TDeltav), the p-alkylbenzene is
From equation (8)
V o ＝V o "×[120.00067×(20-50)]＝0.9799V o ″ (10)
The temperature correction coefficient when the concentration of dissolved gas in the alkylbenzene insulating oil was corrected from 50℃to 20℃was 0.926.
In some embodiments, the method for determining the concentration of dissolved gas in an alkylbenzene insulating oil comprises the steps of: the method comprises the steps of removing gas to be detected from alkylbenzene insulating oil by a mechanical oscillation method, detecting the concentration of characteristic gas to be detected in the removed gas by a gas chromatograph, and calculating the concentration Ci of each component of dissolved gas in the oil by using parameters such as Ki value, temperature correction coefficient and the like, wherein the calculation method comprises the following steps:
(1) the volume of gas, vg', equilibrated at room temperature, test pressure was corrected to the volume, vg ", at 50 ℃ and test pressure:
(2) the volume of the oil sample at room temperature, test pressure, vo ', was corrected to the volume at 50 ℃, test pressure, vo':
Vo″＝Vo′[1+0.00067×(50－t)] (14)
(3) the concentration of the components of the dissolved gas in the oil was calculated as follows:
the following symbol signs are used in the above process steps:
ai-peak area given by component i on the integrator, μV.s;
ai, s-peak area given by external standard component i on integrator, μv·s;
ci-concentration of component i in oil, μL/L;
ci, s-concentration of component i in the external standard, μL/L;
ci-the concentration of component i in the gas being measured, μL/L;
ki-the dissolution equilibrium coefficient of component i;
the p-stripping gas is pressure (atmospheric pressure at the time of degassing), kPa;
t-room temperature at test, DEG C;
vg—volume of the stripping gas at a pressure of 101.3kPa and a temperature of 20 ℃, mL;
vg' -measured volume of the stripping gas at test pressure, at temperature t, mL;
vg "-equilibrium gas volume at 50 ℃, mL at test pressure;
vo-the volume of the degassed oil sample at a temperature of 20 ℃, mL;
vo' -measured volume of degassed oil sample at temperature t, mL;
vo "-volume of degassed oil sample at 50 ℃, mL;
ηi-degassing rate of component i by the degassing device.
In a third aspect of the invention, there is provided an application of the concentration measurement method provided in the second aspect of the invention in fault detection of a deep sea insulated cable.
The concentration measuring method can accurately measure the content of the dissolved fault gas in the alkylbenzene insulating oil, and establishes the alkylbenzene insulating oil gas diagnosis standard for researching the gas production characteristics of the alkylbenzene insulating oil under faults.
The following are some specific examples.
The experimental parameters not specified in the following specific examples are preferentially referred to the guidelines given in the application document, and may also be referred to the experimental manuals in the art or other experimental methods known in the art, or to the experimental conditions recommended by the manufacturer.
Domestic alkylbenzene insulating oil, purchased from Jiangsu tairong;
imported alkylbenzene, model T3788, purchased from japan bp petroleum;
example 1
1) And (3) an external calibration method is adopted, and the gas chromatograph is required to be calibrated before the test. Opening a valve of a standard gas steel cylinder, purging residual gas in a pressure reducing valve, extracting 1mL of standard mixed gas for sample injection by using a 1mL glass injector D, and repeating the operation twice, wherein the repeatability of two adjacent calibrations is kept within 1.5% of the average value;
2) And (5) preparing the blank oil. Taking domestic alkylbenzene insulating oil as test oil, respectively taking 200-250 mL of test oil, putting into two special normal-temperature normal-pressure saturators (one of which is parallel), and bubbling and purging with high-purity nitrogen at room temperature for 2-4 hours until other gas components in the oil are completely purged;
3) Preparing an air storage glass injector, namely taking a plurality of 5mL glass injectors A, sucking about 0.5mL of test oil after each glass injector A extracts a small amount of test oil from the inner wall of a syringe barrel for 1-2 times, sleeving a rubber sealing cap, inserting a double-head needle head, vertically upwards inserting the needle head, and slowly discharging air and test oil in the injector to ensure that the test oil is fully filled in the inner wall of the injector without residual air;
4) Connecting an outlet of a 100mL syringe B with an oil outlet, sucking test oil for rinsing, sucking 20mL of blank test oil, sealing the outlet of the syringe by using a rubber sealing cap, and avoiding air bubbles from entering the syringe as much as possible in the process of taking an oil sample;
5) Taking a 5mL glass injector C, connecting a dental 5-gauge needle, cleaning with mixed gas for 1-2 times, extracting about 5mL of standard mixed gas, slowly injecting the gas in the injector C into the injector B, keeping continuous bubbles discharged from the needle tip in oil during air filling, and repeatedly operating for 4 times to fill about 20mL of standard mixed gas;
6) Placing the injector B into a constant temperature timing oscillator, continuously oscillating for 20min, and then standing for 10min;
7) Taking out the injector B from the constant temperature timing oscillator, taking all balance gas in the injector B into the injector A through a double-ended needle head (the gas after the first balance does not need to record the volume of the gas), and extracting 1mL of gas from the injector A by using a 1mL glass injector D (the same gas is used in the step 1) for sample injection analysis;
8) Step 6 is repeated by filling 20mL of nitrogen into the injector B containing the oil sample after the first balancing similarly to the operation in the step 5;
9) Taking out the injector B from the constant temperature timing oscillator, taking all balance gas in the injector B into the injector A through a double-ended needle head, standing for 2min at room temperature, accurately reading and recording the gas volume to 0.1mL, and extracting 1mL of gas from the injector A by using a 1mL glass injector D (the same branch as that used in the step 1) for sample injection analysis;
10 Method a): repeating the steps 3 to 7 for three times for the same oil test to obtain three groups of data;
method B: and (3) repeating the steps 3 to 9 for three times for the same oil test to obtain three groups of data.
11 Method a and method B): repeating the steps 3 to 10 for the parallel sample;
12 Correcting and calculating the volume of the gas and the test oil after balancing at room temperature according to the formula (4) and the formula (5);
13 Referring to methods A and B, the dissolved gas equilibrium coefficient ki of each gas component at 50℃and 101.3kPa was calculated by referring to formulas (4) and (5).
Example 2
The dissolved gas equilibrium coefficient was measured by substantially the same measurement method as in example 1, except that the imported alkylbenzene insulating oil was used as the test oil.
The test results of examples 1 and 2 are shown in tables 2 to 4 below.
TABLE 2 measurement of dissolved gas balance coefficient of domestic alkylbenzene oil parallel sample
TABLE 3 measurement of dissolved gas balance coefficient of parallel sample of imported alkylbenzene oil
| Component uL/L | First time | Second time | Third time | Average value of | Test method |
| CH 4 | 0.44 | 0.43 | 0.42 | 0.43 | Method B |
| C 2 H 4 | 1.73 | 1.74 | 1.69 | 1.72 | Method A |
| C 2 H 6 | 2.42 | 2.41 | 2.34 | 2.39 | Method A |
| C 2 H 2 | 1.51 | 1.50 | 1.50 | 1.50 | Method A |
| H 2 | 0.08 | 0.08 | 0.08 | 0.08 | Method B |
| CO | 0.14 | 0.15 | 0.14 | 0.14 | Method B |
| CO 2 | 1.13 | 1.12 | 1.15 | 1.13 | Method A |
Table 3 results of testing the solubility balance of two types of alkylbenzene insulating oils and comparison with the results of measuring the solubility balance of mineral insulating oils
In table 3, data for a typical mineral insulating oil is obtained with reference to GB 17623;
as can be seen from table 3, the alkylbenzene insulating oil dissolution balance coefficient test results obtained by the method a and the method B were greatly different from the typical mineral insulating oil dissolution balance coefficient.
All documents mentioned in this application are incorporated by reference as if each were individually incorporated by reference. Unless otherwise contradicted by purpose and/or technical solution of the present application, the cited documents related to the present invention are incorporated by reference in their entirety for all purposes. When reference is made to a cited document in the present invention, the definitions of the relevant technical features, terms, nouns, phrases, etc. in the cited document are also incorporated. In the case of the cited documents, examples and preferred modes of the cited relevant technical features are incorporated into the present application by reference, but are not limited to the embodiments that can be implemented. It should be understood that when a reference is made to the description herein, it is intended to control or adapt the present application in light of the description herein.
The technical features of the above-described embodiments and examples may be combined in any suitable manner, and for brevity of description, all of the possible combinations of the technical features of the above-described embodiments and examples are not described, however, as long as there is no contradiction between the combinations of the technical features, they should be considered to be within the scope described in the present specification.
The above examples merely represent a few embodiments of the present invention and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Further, it is understood that various changes and modifications of the present invention may be made by those skilled in the art after reading the above teachings, and equivalents thereof are intended to fall within the scope of the present invention. It should also be understood that, based on the technical solutions provided by the present invention, those skilled in the art obtain technical solutions through logical analysis, reasoning or limited experiments, all of which are within the scope of protection of the appended claims. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
Claims (13)
1. The method for measuring the Ostwald coefficient of dissolved gas in the alkylbenzene insulating oil is characterized by comprising the following steps:
s100: providing a standard gas comprising a characteristic gas and a protective gas dissolved in an alkylbenzene insulating oil, the characteristic gas having a volume concentration of
S200: adding alkylbenzene insulating oil into a closed container, degassing the alkylbenzene insulating oil, introducing standard gas to ensure that the obtained system reaches the first gas-liquid balance, and measuring the gas phase volume V in the system g Volume of liquid phase V L And the volume concentration C of the characteristic gas g ；
When the Ostwald coefficient of the characteristic gas in the mineral insulating oil is more than or equal to 0.5, calculating k according to a formula (2), namely the Ostwald coefficient;
the characteristic gas has an oswald coefficient of <0.5 in mineral insulating oil, and further comprises the following steps:
s300: discharging all the gas in the closed container, introducing standard gas II to make the obtained system reach secondary gas-liquid balance, and heating at temperature T 1 The gas phase volume V 'of the system was measured as follows' g Volume of liquid phase V' L The volume concentration C 'of the characteristic gas' g The method comprises the steps of carrying out a first treatment on the surface of the The volume of the gas phase V' g Converted into temperature T 2 The volume V' of the gas phase below g The volume of the liquid phase V' L Converted into temperature T 2 The volume V' of the liquid phase L ；
Calculating k' according to a formula (3), namely obtaining the Ostwald coefficient;
2. the method according to claim 1, wherein in the step S100, the volume concentration of the characteristic gas is determinedThe range is generally selected from 5uL/L to 5000uL/L.
3. The method according to claim 1, wherein the volume ratio of the blank oil I obtained after the deaeration in the step S200 to the standard gas introduced is 1:1.
4. The method according to claim 1, wherein the volume ratio of the blank oil II obtained after the total gas is discharged in the step S300 to the standard gas II is 1:1.
5. The method for measuring ostwald coefficient according to any one of claims 2 to 4, wherein when the characteristic gas is carbon dioxide, ethylene, ethane or acetylene, k is calculated according to formula (2), which is the ostwald coefficient;
and when the characteristic gas is hydrogen, carbon monoxide or methane, calculating k' according to a formula (3), namely obtaining the Ostwald coefficient.
6. The method for measuring ostwald coefficient according to claim 1, wherein in step S200, alkylbenzene insulating oil is added into a closed container, and high-purity nitrogen is bubbled and purged for 2 to 4 hours, so as to degas the alkylbenzene insulating oil.
7. The method for measuring the ostwald coefficient according to claim 1, wherein in the step S200, after the standard gas is introduced, the system is continuously oscillated in a constant temperature timing oscillator for 10-30 min, and then is stationary for 5-15 min, so that the obtained system reaches the first gas-liquid equilibrium.
8. The method of measuring an ostwald coefficient according to claim 1, wherein in the step S200, after the standard gas is introduced, the temperature T is set to 2 Under constant pressure, the resulting system reaches a first gas-liquid equilibrium.
9. The method for measuring an ostwald coefficient according to any one of claims 6 to 8, wherein in said step S300, said temperature T 2 Is 50 ℃.
10. The method according to any one of claims 6 to 8, wherein in step S300, high-purity nitrogen is bubbled and purged for 2 to 4 hours, and all the gas in the closed vessel is discharged.
11. The method according to any one of claims 6 to 8, wherein in step S300, after introducing the standard gas II, the system is continuously oscillated in a constant temperature timing oscillator for 10 to 30 minutes and then is stationary for 5 to 15 minutes, so that the obtained system reaches the second gas-liquid equilibrium.
12. The method for measuring the Ostwald coefficient according to claim 1, characterized in that the gas phase volume V 'is determined according to the formula (4)' g Converted into temperature T 2 The volume V' of the gas phase below g ；
The volume of the liquid phase V 'is determined according to formula (5)' L Converted into temperature T 2 The volume V' of the liquid phase L ；
V″ L ＝V′ L ×[1+α×(T 2 -T 1 )] (5)；
Alpha is the thermal expansion coefficient of the alkylbenzene insulating oil.
13. The method for determining the ostwald coefficient of claim 12, further comprising the step of determining the thermal expansion coefficient α of said alkylbenzene insulating oil: selecting a temperature point T with a temperature difference between 5 ℃ and 14 ℃ within a temperature range of 20 ℃ to 90 DEG C 3 And T 4 And T is 3 ＞T 4 The method comprises the steps of carrying out a first treatment on the surface of the Respectively measuring the temperature T 3 And said temperature T 4 The density ρ of the alkylbenzene insulating oil described below 1 And ρ 2 ；
Calculating alpha according to a formula (6);
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