CN113092310A - Transformer oil gas content testing device and method for measuring density by U-shaped oscillation tube - Google Patents
Transformer oil gas content testing device and method for measuring density by U-shaped oscillation tube Download PDFInfo
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- 230000010355 oscillation Effects 0.000 title claims abstract description 149
- 238000012360 testing method Methods 0.000 title claims abstract description 87
- 238000000034 method Methods 0.000 title claims abstract description 61
- 238000009849 vacuum degassing Methods 0.000 claims abstract description 48
- 239000000523 sample Substances 0.000 claims description 99
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 28
- 238000007872 degassing Methods 0.000 claims description 25
- 238000004321 preservation Methods 0.000 claims description 25
- 239000012723 sample buffer Substances 0.000 claims description 25
- 238000005259 measurement Methods 0.000 claims description 19
- 239000000126 substance Substances 0.000 claims description 17
- 230000005284 excitation Effects 0.000 claims description 15
- 230000008569 process Effects 0.000 claims description 14
- 238000009413 insulation Methods 0.000 claims description 6
- 229920001296 polysiloxane Polymers 0.000 claims description 4
- 238000005086 pumping Methods 0.000 claims description 4
- 238000007599 discharging Methods 0.000 claims description 3
- 238000001514 detection method Methods 0.000 abstract description 14
- 230000008859 change Effects 0.000 abstract description 11
- 239000003921 oil Substances 0.000 description 171
- 239000007789 gas Substances 0.000 description 79
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 12
- 230000006872 improvement Effects 0.000 description 12
- 229910002092 carbon dioxide Inorganic materials 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 239000001569 carbon dioxide Substances 0.000 description 6
- 230000008901 benefit Effects 0.000 description 5
- 239000011521 glass Substances 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 2
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 238000001739 density measurement Methods 0.000 description 2
- 238000010828 elution Methods 0.000 description 2
- 238000011010 flushing procedure Methods 0.000 description 2
- 238000004817 gas chromatography Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 230000032683 aging Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 125000004435 hydrogen atom Chemical class [H]* 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000010358 mechanical oscillation Effects 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
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- 238000006467 substitution reaction Methods 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 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
- G01N9/00—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
- G01N9/36—Analysing materials by measuring the density or specific gravity, e.g. determining quantity of moisture
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Abstract
The invention discloses a transformer oil gas content testing device and method for testing density by a U-shaped oscillation tube, belongs to the technical field of power system detection, and solves the problem of how to calculate the gas content in oil according to the density change of an oil sample before and after vacuum degassing of the tested oil sample so as to improve the testing precision.
Description
Technical Field
The invention belongs to the technical field of power system detection, and relates to a transformer oil gas content testing device and method for testing density by using a U-shaped oscillation tube.
Background
The carbon dioxide elution method is characterized in that dissolved gas in oil is replaced and carried out by utilizing supersaturation of carbon dioxide, then the carbon dioxide is completely absorbed by alkali liquor through an absorption tube filled with potassium hydroxide solution, so that all the dissolved gas in the oil enters a gas measuring tube, and the content of the dissolved gas in the oil is measured according to the content. However, the carbon dioxide elution method has a problem that CO is present in the method2The flow rate is not easy to be controlled accurately, and the potassium hydroxide solution is used for CO2The problems of absorption efficiency, blank value measurement and the like need to be studied carefully, and more importantly, the method is only suitable for measuring the gas content of new oil and is used for CO fault generated by operating equipment2The gas is not detected, so that the measurement result is low. The method has the characteristics of difficult test control, poor test precision, narrow applicability and the like, so that the method is basically not used for testing the gas content of the transformer oil at present.
The gas chromatography is the most widely used method for detecting the gas content of the transformer oil at present, and the detection method mainly comprises the steps of removing gas in the transformer oil by using a mechanical oscillation method or an automatic headspace degassing method, separating and detecting each gas component by using a gas chromatograph, calculating a result, and expressing the calculated result by volume fraction (%) so as to obtain the gas content of the transformer oil. The gas chromatography has high detection precision and good repeatability, but has long detection time, more manual links in the degassing process and great influence on the detection result. The requirement on the gas content index is high (the gas content requirement after the oil injection of the transformer oil of 1000kV equipment is less than or equal to 0.8%), which puts a severe requirement on the precision of detection instruments and equipment, and the oil sample can only be tested in a laboratory due to the limitation of experimental conditions. However, the transformer oil sample in the equipment is taken back to the laboratory from the field by using the sealed needle tube to be detected, the influence of human factors and environmental factors on the detection process is too large, and even if the instruments in the laboratory are more precise and the detection process is more precise, the detection result still can have larger errors.
The method for measuring the gas content in the insulating oil by using the vacuum differential pressure method is mainly characterized in that an oil sample to be measured enters a high-vacuum degassing chamber through a proper mode, so that dissolved gas in test oil is rapidly released, the content of the dissolved gas in the oil is calculated by combining parameters such as room temperature, the oil test quantity, the volume of the degassing chamber, the temperature of the degassing chamber and the like according to the pressure difference generated by the released gas before and after the test oil enters the degassing chamber, and the gas content in the oil sample to be measured is expressed by the volume fraction (%) of the gas to the test oil under standard conditions (101.3kPa and 0 ℃), and the method is also called as a total degassing method.
The vacuum differential pressure method has the advantage of rapid and accurate measurement. The vacuum differential pressure method is classified into a U-shaped column differential pressure method and an electronic vacuum gauge differential pressure method depending on the vacuum gauge used.
The U-shaped oil column differential pressure gauge method has high requirements on the tightness of instruments and equipment, and in addition, toxic pure mercury is used, so that the degassing is incomplete due to low instrument precision, and when the vacuum degree has small deviation, the measurement of the gas content has large errors. And the detection operation is complex, and the requirement on the operation proficiency of testers is high.
The instrument used by the differential pressure method of the electronic vacuum gauge consists of a metal container, an electronic vacuum device, an electronic measuring device and an electronic control device, the device has the advantages of high intelligent degree, simple test operation, high accuracy and the like, and the measurement of the gas content on site can be realized along with the increase of the integration degree of the device. For example, in the prior art, chinese patent application publication No. CN107063920A, published as 2017, 8, 18 and 18, discloses an improved vacuum differential pressure method for an electronic vacuum gauge, which realizes absolute vacuum in an initial state by moving a piston, and realizes measurement of the gas content in insulating oil without pre-vacuumizing, and the improved method can realize rapid detection of the gas content on site.
However, the pressure difference method measurement principle of the existing electronic vacuum gauge is that a certain volume of transformer oil is degassed under a vacuum condition, the degassing degree is reduced by degassing, and the gas content is calculated according to the change of the vacuum degree. That is, the volume of the transformer oil used in the test was constant, the amount of gas contained in the oil was different, and the amount of change in the degree of vacuum of the degassing vessel was also different. Due to the fact that the difference of the gas contents of the transformer oil under different conditions is large, the gas content of the oil in the open type oil tank can reach about 10%, and the requirement of the gas content of the extra-high voltage oil after hot oil circulation is not higher than 0.8%. For oils with different gas contents, it is clear that the degassing degree is different, the absolute amount of the degassing gas is different, and the variation of the vacuum degree of the device shown by the test result is also different. In order to increase the degassing efficiency of low-gas-content oil, it is common to increase the vacuum volume, i.e. the volume of the degassing vessel, and although the degassing efficiency is increased, the gas component concentration in the gas phase is reduced and the corresponding change in the differential pressure of the vacuum gauge is reduced, which places higher demands on the precision of the apparatus.
Disclosure of Invention
The invention aims to calculate the gas content in oil according to the change of the density of an oil sample before and after vacuum degassing of the measured oil sample, thereby improving the test precision.
The invention solves the technical problems through the following technical scheme:
the utility model provides a transformer oil gas content testing arrangement of U type oscillating pipe density, includes: the device comprises a U-shaped oscillation tube (1), a magnet (2), an electronic excitation oscillator (3), a vacuum degassing chamber (4), an oil sample buffer chamber (5), a vacuum pump (6), a first temperature sensor (7), a second temperature sensor (8), a third temperature sensor (9), a temperature control heat preservation layer (10), a first valve (11), a second valve (12), a third valve (13), a fourth valve (14), a fifth valve (15), a sixth valve (16) and a frequency counter (17); the U-shaped oscillation tube (1), the magnet (2), the electronic excitation oscillator (3), the vacuum degassing chamber (4), the oil sample buffer chamber (5), the first temperature sensor (7), the third temperature sensor (9), the third valve (13), the fourth valve (14) and the frequency counter (17) are all arranged inside the temperature-controlled heat-insulating layer (10); the top port of the left side of the U-shaped oscillation pipe (1) is connected with an input medium pipeline, the input medium pipeline extends to the outside of the temperature control heat preservation layer (10), and a first valve (11) is arranged on the input medium pipeline; the top port of the right side of the U-shaped oscillation tube (1) is connected with an output medium pipeline, the output medium pipeline extends to the outside of the temperature control heat preservation layer (10), and a second valve (12) is arranged on the output medium pipeline; a magnet (2) is fixed at the bottom of the U-shaped oscillation tube (1), an electronic excitation oscillator (3) is installed at the bottom of the magnet (2), and two vertical tubes of the U-shaped oscillation tube (1) are respectively provided with a frequency counter (17) for measuring the vibration frequency of the U-shaped oscillation tube (1); the vacuum degassing chamber (4) is a closed container, an oil sample buffer chamber (5) is arranged in the vacuum degassing chamber, the upper part of the vacuum degassing chamber (4) is connected with a vacuum pump (6) through a pipeline, a sixth valve (16) is arranged on the connecting pipeline, an emptying pipeline is arranged at the bottom of the vacuum degassing chamber (4), and a fifth valve (15) is arranged on the emptying pipeline; the upper part of the oil sample buffer chamber (5) is open, two interfaces at the lower part of the oil sample buffer chamber are respectively connected with two ports of the U-shaped oscillation tube (1) through pipelines, and a third valve (13) and a fourth valve (14) are respectively arranged on the pipelines; first temperature sensor (7) set up on the inside lateral wall of accuse temperature heat preservation (10), second temperature sensor (8) set up on the outside lateral wall of accuse temperature heat preservation (10), third temperature sensor (9) set up between two standpipes of U type oscillating pipe (1).
The device provided by the invention measures the density of the oil sample by using the U-shaped oscillation tube, has very high measurement precision, and can meet the requirement of accurately measuring the density change of the oil sample before and after degassing.
As a further improvement of the technical scheme of the invention, the left top port and the right top port of the U-shaped oscillation tube (1) are respectively connected with the input medium pipeline and the output medium pipeline through hard silicone tubes.
As a further improvement of the technical scheme of the invention, the absolute residual pressure of the vacuum pump (6) is not more than 10 Pa.
As a further improvement of the technical scheme of the invention, the measurement accuracy of the first temperature sensor (7), the second temperature sensor (8) and the third temperature sensor (9) is +/-0.1 ℃, and the temperature control accuracy of the temperature control heat-preservation layer (10) is +/-0.1 ℃.
The method applied to the transformer oil gas content testing device for measuring the density by the U-shaped oscillating tube comprises the following steps:
s101, calibrating the device; calibrating the U-shaped oscillation tube (1) by respectively adopting clean air and pure water as standard substances, and calculating an instrument constant F of the U-shaped oscillation tube (1);
s102, measuring the density of the oil sample to be measured; the method comprises the steps that the U-shaped oscillation tube (1) is washed by using an oil sample to be detected, and after the oil sample to be detected in the U-shaped oscillation tube (1) is free of bubbles and the temperature reaches a set value and is stable, the density rho of the oil sample to be detected is calculated0；
S103, measuring the density of the oil sample to be measured after vacuum degassing; carrying out vacuum degassing treatment on the oil sample to be detected in the U-shaped oscillation pipe (1) by using a vacuum pump (6), slowly removing dissolved gas in the oil sample to be detected, measuring the degassed oil sample in the U-shaped oscillation pipe (1) after degassing is finished, and calculating the density rho of the oil sample to be detected after vacuum degassing1；
S104, calculating the gas content in the oil sample to be measured; according to rho0、ρ1、ρQi (Qi)And U-shaped oscillation tube volume V0And calculating to obtain the volume V of the gas content of the oil sample to be measuredQi (Qi)And calculating the gas content G of the oil sample to be measured.
The method provided by the invention calculates the gas content in the oil according to the density change of the oil sample before and after vacuum degassing of the tested oil sample for the first time, is a testing method based on a brand-new testing principle, is simple to operate, facilitates the field test, and can adapt to the measurement of oil samples with different gas contents.
As a further improvement of the technical scheme of the invention, the process of calibrating the U-shaped oscillation tube (1) by using clean air as a standard substance in the step S101 comprises the following steps: before starting testing, all valves are in a closed state, at the moment, a first valve (11) and a second valve (12) are opened, clean air is introduced into the device from the first valve (11), the U-shaped oscillation pipe (1) is swept for not less than 10min, the first valve (11) and the second valve (12) are closed successively, the temperature control function is started through a temperature control heat insulation layer (10), after the temperatures of a first temperature sensor (7), a second temperature sensor (8) and a third temperature sensor (9) are stabilized at 20 +/-0.1 ℃, the testing function of the device is started, a magnet (2) is enabled to generate oscillation with fixed frequency through an electronic excitation oscillator (3), and the oscillation period T is recorded through a frequency counter (17) and the third temperature sensor (9)AAnd temperature tAAfter that, the test is ended.
As a further improvement of the technical scheme of the invention, the process of calibrating the U-shaped oscillation tube (1) by using pure water as a standard substance in the step S101 comprises the following steps: before the test is started, all the valves are in a closed state, the first valve (11) and the second valve (12) are opened, pure water enters the U-shaped oscillating pipe (1) through the first valve (11), and is discharged from the second valve (12), the U-shaped oscillating pipe (1) and the pipeline are washed for 3-5 min by pure water, the first valve (11) and the second valve (12) are closed successively after no bubble exists in the U-shaped oscillating pipe (1) and the pipeline, the temperature control function is started through the temperature control heat preservation layer (10), after the temperatures of the first temperature sensor (7), the second temperature sensor (8) and the third temperature sensor (9) are stabilized at 20 +/-0.1 ℃, the test function of the device is started, the magnet (2) is caused to oscillate at a fixed frequency by electronically exciting the oscillator (3), the oscillation period T is recorded by a frequency counter (17) and a third temperature sensor (9).WAnd temperature tW(ii) a After the process is finished, pure water in the U-shaped oscillating pipe (1) is discharged, the first valve (11) and the second valve (12) are opened, and then dry clean air is introduced from the first valve (11) to lead the U-shaped oscillating pipe(1) And after the corresponding pipeline is dried, closing all the valves.
As a further improvement of the technical solution of the present invention, the process of determining the density of the oil sample to be measured in step S102 is as follows: before the test is started, all valves are in a closed state, a first valve (11) and a second valve (12) are opened, an oil sample to be tested enters a U-shaped oscillation tube (1), the U-shaped oscillation tube (1) is flushed for 3-5 min by the oil sample to be tested, then a third valve (13), a fourth valve (14) and a fifth valve (15) are opened, the second valve (12) is closed, the oil sample to be tested enters an oil sample buffer chamber (5) from the third valve (13) and the fourth valve (14) to be flushed, and the flushed oil sample is discharged through the fifth valve (15); when an oil sample to be tested is filled with the U-shaped oscillation pipe (1), the oil sample buffer chamber (5) and the corresponding pipeline and no air bubble exists in oil, the first valve (11), the third valve (13), the fourth valve (14) and the fifth valve (15) are closed, the temperature control function is started through the temperature control heat preservation layer (10), the first temperature sensor (7), the second temperature sensor (8) and the third temperature sensor (9) are stabilized at 20 +/-0.1 ℃, the test function of the device is started, the magnet (2) is enabled to generate oscillation with fixed frequency through the electronic excitation oscillator (3), and the oscillation period T is recorded through the frequency counter (17) and the third temperature sensor (9)0And temperature t0。
As a further improvement of the technical scheme of the present invention, the process of density measurement after vacuum degassing of the oil sample to be measured in step S103 is as follows: opening a third valve (13), a fourth valve (14) and a sixth valve (16), opening a vacuum pump (6), vacuumizing and degassing the oil sample, keeping the vacuum degree at-0.05 Mpa, vacuumizing for 10min, adjusting the vacuum degree to-0.1 Mpa, continuously vacuumizing for 20min, closing the vacuum pump (6) and the sixth valve (16), starting a temperature control function through a 10-temperature control heat insulation layer, starting a test function of the device after the temperatures of the first temperature sensor (7), the second temperature sensor (8) and the third temperature sensor (9) are stabilized at 20 +/-0.1 ℃, exciting the oscillator (3) through electrons to enable the magnet (2) to generate oscillation with fixed frequency, and recording an oscillation period T through a frequency counter (17) and the third temperature sensor (9)1And temperature t1After the test is finished, the fifth valve (15) is opened to balance the pressure of the vacuum degassing chamber (4) to the atmospheric pressure, and the first valve is opened(11) And a second valve (12) for discharging the oil sample in the U-shaped oscillation tube (1).
As a further improvement of the technical scheme of the invention, the calculation formula of the instrument constant F is as follows:
in the formula: rhoWDenotes the density, ρ, of pure water at the test temperatureARepresents the density of clean air at the test temperature; t isWRepresenting the vibration period observed when pure water is in the U-shaped oscillation tube; t isAShowing the vibration period observed when clean air is present in the U-shaped oscillating duct.
As a further improvement of the technical scheme of the invention, the density rho of the oil sample to be measured is calculated in step S1020The formula of (1) is:
in the formula, T0Showing the vibration period observed by the oil sample to be measured before vacuum degassing in the U-shaped oscillation tube.
As a further improvement of the technical scheme of the invention, the density rho of the oil sample to be measured after vacuum degassing is calculated in step S1031The formula of (1) is:
in the formula, T1The vibration period observed for the oil sample to be measured after vacuum degassing in the U-shaped oscillation tube is shown.
As a further improvement of the technical scheme of the invention, the gas content volume V of the oil sample to be measured is calculated in the step S104Qi (Qi)The formula of (1) is:
ρ1V0-ρ0V0＝ρqi (Qi)VQi (Qi)
In the formula, ρQi (Qi)Indicating the density, V, of the gas contained in the oil sample to be measured0Indicating volume, V, of U-shaped oscillating tubeQi (Qi)Representing the volume occupied by the gas in the oil sample to be measured.
As a further improvement of the technical solution of the present invention, the formula for calculating the gas content G of the oil to be measured in step S104 is:
wherein t represents the constant temperature of the test apparatus, and 0.0008 represents the thermal expansion coefficient of the oil, in units of 1/DEG C.
The invention has the advantages that:
(1) the invention provides the method for calculating the gas content in the oil according to the density change of the oil sample before and after vacuum degassing of the tested oil sample for the first time, and the method is a testing method of a brand new testing principle, measures the density of the oil sample by utilizing the U-shaped oscillating tube, has very high measuring precision, can meet the accurate measurement of the density change of the oil sample before and after degassing, is simple to operate, is convenient for carrying out the test on site, and can adapt to the measurement of the oil samples with different gas contents;
(2) the oil sample to be tested in the U-shaped oscillation tube is directly vacuumized, and then is immediately tested after being vacuumized, so that gas redissolution is effectively avoided; meanwhile, the degassing time of the vacuum pump can be controlled to flexibly realize the rapid measurement and the accurate measurement of the gas content;
(3) the designed oil sample buffer chamber can reduce the disturbance of the vacuum degassing process on the oil sample in the U-shaped oscillation tube, so that the pressure at two ends of the U-shaped oscillation tube is balanced;
(4) the device can be directly connected to oil-using power equipment and used for on-line monitoring of the gas content of transformer oil.
Drawings
FIG. 1 is a schematic structural diagram of a transformer oil gas content testing device for measuring density by a U-shaped oscillation tube according to an embodiment of the invention;
FIG. 2 is a flow chart of a method for testing gas content of transformer oil by using a U-shaped oscillation tube to measure density according to an embodiment of the invention;
reference numerals in the drawings: the device comprises a 1-U-shaped oscillation tube, a 2-magnet, a 3-electronic excitation oscillator, a 4-vacuum degassing chamber, a 5-oil sample buffer chamber, a 6-vacuum pump, a 7-first temperature sensor, a 8-second temperature sensor, a 9-third temperature sensor, a 10-temperature control and insulation layer, a 11-first valve, a 12-second valve, a 13-third valve, a 14-fourth valve, a 15-fifth valve, a 16-sixth valve and a 17-frequency counter.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The technical scheme of the invention is further described by combining the drawings and the specific embodiments in the specification:
example one
1. Connection relation of devices
As shown in fig. 1, a transformer oil gas content testing device for measuring density by a U-shaped oscillation tube includes: the device comprises a U-shaped oscillation tube 1, a magnet 2, an electronic excitation oscillator 3, a vacuum degassing chamber 4, an oil sample buffer chamber 5, a vacuum pump 6, a first temperature sensor 7, a second temperature sensor 8, a third temperature sensor 9, a temperature-controlled heat-insulating layer 10, a first valve 11, a second valve 12, a third valve 13, a fourth valve 14, a fifth valve 15, a sixth valve 16 and a frequency counter 17.
The U-shaped oscillation tube 1, the magnet 2, the electronic excitation oscillator 3, the vacuum degassing chamber 4, the oil sample buffer chamber 5, the first temperature sensor 7, the third temperature sensor 9, the third valve 13, the fourth valve 14 and the frequency counter 17 are all arranged in the temperature control heat preservation layer 10; the U-shaped oscillation tube 1 is made of boronized glass, the volume of the U-shaped oscillation tube is 3mL, the U-shaped oscillation tube is calibrated by a pure water injection weighing method, the top port of the left side of the U-shaped oscillation tube 1 is connected with an input medium pipeline through a hard silicone tube, the input medium pipeline extends to the outside of the temperature control heat preservation layer 10, and a first valve 11 is arranged on the input medium pipeline; the top port of the right side of the U-shaped oscillation tube 1 is connected with an output medium pipeline through a hard silicone tube, the output medium pipeline extends to the outside of the temperature control heat preservation layer 10, and a second valve 12 is arranged on the output medium pipeline; the bottom of the U-shaped oscillation tube 1 is fixed with a magnet 2, the bottom of the magnet 2 is provided with an electronic excitation oscillator 3, and two vertical tubes of the U-shaped oscillation tube 1 are respectively provided with a frequency counter 17 for measuring the vibration frequency of the U-shaped oscillation tube 1.
The vacuum degassing chamber 4 is a closed container, an oil sample buffer chamber 5 is arranged in the vacuum degassing chamber 4, and the vacuum degassing chamber 4 is used for carrying out vacuum degassing on the oil sample; the upper part of the vacuum degassing chamber 4 is connected with a vacuum pump 6 through a pipeline, a sixth valve 16 is arranged on the connecting pipeline, an emptying pipeline is arranged at the bottom of the vacuum degassing chamber 4, and a fifth valve 15 is arranged on the emptying pipeline; the absolute residual pressure of the vacuum pump 6 is not more than 10 Pa.
The oil sample buffer chamber 5 is a glass container, the volume of the glass container is 3mL, the upper part of the oil sample buffer chamber 5 is open, two interfaces at the lower part of the oil sample buffer chamber are respectively connected with two ports of the U-shaped oscillating tube 1 through pipelines, and a third valve 13 and a fourth valve 14 are respectively arranged on the pipelines; the oil sample buffer chamber 5 has two functions, one is used for relieving the disturbance of the vacuumizing process on the oil sample in the U-shaped oscillation tube 1, and simultaneously ensures that the vacuum functions of two ports of the U-shaped oscillation tube 1 are the same; the other function is to buffer the oil sample in the U-shaped oscillation tube 1, during the vacuum pumping process, bubbles are separated from the oil and move upwards, the oil in the U-shaped oscillation tube 1 is discharged by the bubbles, so that the volume of the oil in the U-shaped oscillation tube 1 changes, at this time, the oil sample in the upper oil sample replenishing chamber automatically flows downwards to replenish the U-shaped oscillation tube 1, and the situation that the oil amount in the U-shaped oscillation tube 1 is not full due to the vacuum pumping is prevented.
The first temperature sensor 7 is arranged on the inner side wall of the temperature-control heat-preservation layer 10, the second temperature sensor 8 is arranged on the outer side wall of the temperature-control heat-preservation layer 10, and the third temperature sensor 9 is arranged between the two vertical pipes of the U-shaped oscillation pipe 1; the temperature sensor is used for measuring the temperature of the heating body, the temperature of the external environment and the temperature in the U-shaped oscillating tube 1 respectively, and the measurement precision of the temperature sensor is +/-0.1 ℃.
The temperature control heat preservation layer 10 is used for adjusting and controlling the temperature of a test area, and comprises a temperature control function and a heat preservation function, the temperature control function controls the temperature of the test area by controlling the time of the Peltier heating element through the micro processor, and the temperature control precision is +/-0.1 ℃.
2. Principle of detection of the device
The U-shaped oscillation tube is widely applied to density detection of liquid and gas, and has the advantages of rapidness, reliability, high accuracy, high measurement precision and the like. The principle of the U-shaped oscillation tube method for detecting the density of a substance is that the oscillation frequency of a glass U-shaped oscillation tube based on electromagnetic initiation is utilized, namely a magnet is fixed on the U-shaped oscillation tube, an oscillator is excited by electrons to generate vibration, the vibration period of the U-shaped oscillation tube is measured by a vibration sensor, and each U-shaped oscillation tube has the characteristic frequency or vibrates according to the natural frequency. When the U-shaped oscillation tube is filled with an object, the frequency of the U-shaped oscillation tube is a function of the mass of the filling material in the tube. The frequency of the mass decreases as it increases, i.e. the period T of oscillation increases. During measurement, certain substances are selected as standard substances, and the density value of the measured substance is calculated through the difference of the vibration frequency between the measured substance and the standard substances after the frequency is measured.
The U-shaped oscillation tube needs to measure an instrument constant F before testing, and is usually measured by at least two standard substances, wherein the density interval of the two standard substances is required to cover the density range of a test sample. For transformer oil, the density is generally 890kg/m3～900kg/m3In the range of (20 ℃), therefore, the clean air and the pure water can be selected as the standard substances, and the constant F of the device can be calculated according to the density measurement result of the standard substances by the U-shaped oscillation tube:
in equation (1): f represents a constant of the U-shaped oscillation tube tester; rhoWThe density of pure water at the test temperature is expressed in g/cm3(at 20 ℃ C.). sup.w＝0.9982g/cm3)；ρAThe density of the clean air at the test temperature is expressed in g/cm3(at 20 ℃ C.). sup.A＝0.00120g/cm3)；TWThe unit of the vibration period is s, which represents the vibration period observed when pure water is filled in the U-shaped oscillation tube; t isAThe vibration period observed when clean air is present in the U-shaped oscillation tube is represented by s.
Therefore, the oil sample is detected by using the U-shaped oscillation tube, and the vibration period T of the oil sample is measuredOilThe density ρ of the oil can be obtainedOil：
In the formula (2), ρOilThe density of the oil sample at the test temperature is expressed in g/cm3；ρWThe density of pure water at the test temperature is expressed in g/cm3；TWThe unit of the vibration period is s, which represents the vibration period observed when pure water is filled in the U-shaped oscillation tube; t isOilThe vibration period observed when an oil sample is present in the U-shaped oscillation tube is represented by s.
The principle of the U-shaped oscillating tube method for measuring the gas content of the transformer oil is based on the measurement and calculation of the density change of the oil caused by the gas contained in the oil. Firstly, the density rho of an untreated oil sample to be measured is measured by using a U-shaped oscillation tube oscillation method0Then, gas contained in the oil is removed by a vacuum degassing mode, and the density of the oil sample after gas removal is measured as rho through a U-shaped oscillation tube oscillation method1Since the gas dissolved in the oil has little effect on the volume of the oil, it is considered that the volume of the oil does not change before and after degassing, and then:
ρ1V0-ρ0V0＝ρqi (Qi)VQi (Qi) (3)
In the formulae (3) and (4) (. rho)0The unit of the density of the oil to be measured is g/mL; rho1Represents the density of the oil after vacuum degassing in g/mL; rhoQi (Qi)Density of gas contained in oil, unit is g/mL; v0The volume of the U-shaped oscillation tube is expressed in mL; vQi (Qi)Represents the volume of gas in the oil in mL.
The gas species contained in the transformer oil include clean air (oxygen and nitrogen), carbon dioxide, carbon monoxide, and gaseous hydrocarbons and hydrogen, which are generally produced by the breakdown of oil due to equipment failure, and the content of oil is very low, 10%-5～10-7The concentration range of L/L is approximately in the range of 0.001-0.00001% in terms of gas content; the carbon monoxide and carbon dioxide contents generally do not exceed 10-3L/L, converted into gas content is generally less than 0.1%. That is to say, the gas contained in the transformer oil is mainly clean air, which is the reason for determining whether the equipment has a clean air leakage point by testing the gas content. Because the aging process of the transformer oil and the insulating paper consumes oxygen, according to the analysis and judgment guide rule of the dissolved gas in the transformer oil (DL/T722) 2014 in the power industry standard, in the well-sealed oil-filled equipment, the ratio of the oxygen to the nitrogen is even less than 0.05, so that the gas extracted from the transformer oil is basically nitrogen and trace other gases. Meanwhile, as shown in the formula (4), when ρ isQi (Qi)The smaller, VQi (Qi)The larger, and therefore in uncertainty ρQi (Qi)When the exact value of (1) is rhoN2Instead of rhoQi (Qi)Let V beQi (Qi)The real value is larger, and the safety is higher in practical application.
From VQi (Qi)And V0Calculating the gas content of the measured oil sample:
in the formula (5), G represents oilMedium gas content, in%; vQi (Qi)Represents the volume of gas in oil in mL; v0The volume of the U-shaped oscillation tube is expressed in mL; t represents the constant temperature of the test apparatus in units of ℃; 0.0008 represents the coefficient of thermal expansion of the oil in units of 1/deg.C.
3. Operation procedure of device
(1) Device calibration
The device needs to be calibrated when in use for the first time, and clean air and pure water are used as standard substances to calibrate the U-shaped oscillating pipe. Firstly, clean air is introduced into the U-shaped oscillation tube 1, and after the temperatures of the clean air and the U-shaped oscillation tube 1 reach the set temperature and are stable, the vibration period T is recordedAAnd the temperature t of the U-shaped oscillation tube 1AThen, injecting pure water into the U-shaped oscillation tube, wherein no bubble exists in the pure water in the tube, and recording the vibration period T after the pure water and the temperature of the U-shaped oscillation tube 1 reach the set temperature and are stablewAnd the temperature t of the U-shaped oscillation tube 1wAnd calculating a constant F of the U-shaped oscillation tube tester according to the formula (1).
(a) Clean air calibration: before the test is started, all valves are in a closed state, at the moment, the first valve 11 and the second valve 12 are opened, clean air is introduced into the device from the first valve 11, the U-shaped oscillation pipe 1 is purged for not less than 10min, the first valve 11 and the second valve 12 are closed successively, the temperature control function is started through the temperature control heat preservation layer 10, after the temperatures of the first temperature sensor 7, the second temperature sensor 8 and the third temperature sensor 9 are stabilized at 20 +/-0.1 ℃, the test function of the device is started, the oscillator 3 is excited through electrons to enable the magnet 2 to generate oscillation with fixed frequency, and the oscillation period T is recorded through the frequency counter 17 and the third temperature sensor 9AAnd sensor temperature tAAfter that, the test is ended.
(b) Pure water calibration: before the test is started, all the valves are in a closed state, the first valve 11 and the second valve 12 are opened, pure water enters the U-shaped oscillating pipe 1 through the first valve 11 and is discharged from the second valve 12, the U-shaped oscillating pipe 1 and the corresponding pipeline are slowly flushed for 3-5 min by the pure water, and after no bubbles exist in the U-shaped oscillating pipe 1 and the corresponding pipeline, the first valve 11 and the second valve are closed successivelyThe door 12 starts the temperature control function through the temperature control heat preservation layer 10, after the temperatures of the first temperature sensor 7, the second temperature sensor 8 and the third temperature sensor 9 are stabilized at 20 +/-0.1 ℃, the testing function of the device is started, the magnet 2 is enabled to generate oscillation with fixed frequency through the electronic excitation oscillator 3, and the oscillation period T is recorded through the frequency counter 17 and the third temperature sensor 9WAnd sensor temperature tW。
After the test is finished, pure water in the U-shaped oscillation pipe 1 is discharged, the first valve 11 and the second valve 12 are opened, dry pure clean air is introduced from the first valve 11 to blow the U-shaped oscillation pipe 1 and corresponding pipelines dry, and then all the valves are closed.
(2) Density determination of oil sample to be measured
The U-shaped oscillation tube 1 is washed by the oil sample to be detected, and the vibration period T is measured and recorded after the oil sample to be detected in the U-shaped oscillation tube 1 has no bubbles and the temperature reaches a set value and is stable0And temperature t0Calculating the density rho of the oil to be measured according to the formula (2)0。
Before the test is started, opening a first valve 11 and a second valve 12 to enable an oil sample to be tested to enter a U-shaped oscillation pipe 1, slowly flushing the U-shaped oscillation pipe 1 for 3-5 min by using the oil sample to be tested, then opening a third valve 13, a fourth valve 14 and a fifth valve 15, closing the second valve 12, enabling the oil sample to be tested to enter an oil sample buffer chamber 5 from the third valve 13 and the fourth valve 14 for flushing, and discharging the flushed oil sample through the fifth valve 15; when the oil sample to be tested is filled with the U-shaped oscillation tube 1, the oil sample buffer chamber 5 and the corresponding pipeline and no air bubble exists in the oil, the first valve 11, the third valve 13, the fourth valve 14 and the fifth valve 15 are closed, the temperature control function is started through the temperature control heat preservation layer 10, the testing function of the device is started after the temperatures of the first temperature sensor 7, the second temperature sensor 8 and the third temperature sensor 9 are stabilized at 20 +/-0.1 ℃, the oscillator 3 is excited through electrons to enable the magnet 2 to generate oscillation with fixed frequency, and the oscillation period T is recorded through the frequency counter 17 and the third temperature sensor 90And sensor temperature t0。
(3) Density determination of oil sample to be measured after vacuum degassing
Carrying out vacuum degassing treatment on the oil sample to be tested in the U-shaped oscillation pipe 1 by using a vacuum pump 6, slowly removing dissolved gas in the oil sample to be tested, measuring degassed oil in the U-shaped oscillation pipe 1 after degassing is finished, and recording a vibration period T1And temperature t1Calculating the density rho of the degassed oil according to the formula 21。
Opening a third valve 13, a fourth valve 14 and a sixth valve 16, opening a vacuum pump 6, vacuumizing and degassing the oil sample, keeping the vacuum degree at-0.05 Mpa, vacuumizing for 10min, adjusting the vacuum degree to-0.1 Mpa, continuously vacuumizing for 20min, closing the vacuum pump 6 and the sixth valve 16, starting the temperature control function through a temperature control heat insulation layer 10, starting the test function of the device after the temperatures of the first temperature sensor 7, the second temperature sensor 8 and the third temperature sensor 9 are stabilized at 20 +/-0.1 ℃, exciting the oscillator 3 through electrons to enable the magnet 2 to generate oscillation with fixed frequency, and recording the oscillation period T through a frequency counter 17 and the third temperature sensor 91And sensor temperature t1. After the test is completed, the fifth valve 15 is opened to equalize the pressure in the vacuum degassing chamber 4 to atmospheric pressure, and the first valve 11 and the second valve 12 are opened to discharge the oil sample in the U-shaped oscillation tube 1.
(4) Calculation of gas content in oil sample to be measured
From the oil density rho to be measured0Density of degassed oil ρ1And clean air density ρQi (Qi)And U-shaped oscillation tube volume V0Calculating the volume V of the gas content in the oil according to the formulas (3) and (4)Qi (Qi)And calculating the gas content G of the oil to be measured according to a formula (5).
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (14)
1. The utility model provides a transformer oil air content testing arrangement of U type oscillating pipe density, its characterized in that includes: the device comprises a U-shaped oscillation tube (1), a magnet (2), an electronic excitation oscillator (3), a vacuum degassing chamber (4), an oil sample buffer chamber (5), a vacuum pump (6), a first temperature sensor (7), a second temperature sensor (8), a third temperature sensor (9), a temperature control heat preservation layer (10), a first valve (11), a second valve (12), a third valve (13), a fourth valve (14), a fifth valve (15), a sixth valve (16) and a frequency counter (17); the U-shaped oscillation tube (1), the magnet (2), the electronic excitation oscillator (3), the vacuum degassing chamber (4), the oil sample buffer chamber (5), the first temperature sensor (7), the third temperature sensor (9), the third valve (13), the fourth valve (14) and the frequency counter (17) are all arranged inside the temperature-controlled heat-insulating layer (10); the top port of the left side of the U-shaped oscillation pipe (1) is connected with an input medium pipeline, the input medium pipeline extends to the outside of the temperature control heat preservation layer (10), and a first valve (11) is arranged on the input medium pipeline; the top port of the right side of the U-shaped oscillation tube (1) is connected with an output medium pipeline, the output medium pipeline extends to the outside of the temperature control heat preservation layer (10), and a second valve (12) is arranged on the output medium pipeline; a magnet (2) is fixed at the bottom of the U-shaped oscillation tube (1), an electronic excitation oscillator (3) is installed at the bottom of the magnet (2), and two vertical tubes of the U-shaped oscillation tube (1) are respectively provided with a frequency counter (17) for measuring the vibration frequency of the U-shaped oscillation tube (1); the vacuum degassing chamber (4) is a closed container, an oil sample buffer chamber (5) is arranged in the vacuum degassing chamber, the upper part of the vacuum degassing chamber (4) is connected with a vacuum pump (6) through a pipeline, a sixth valve (16) is arranged on the connecting pipeline, an emptying pipeline is arranged at the bottom of the vacuum degassing chamber (4), and a fifth valve (15) is arranged on the emptying pipeline; the upper part of the oil sample buffer chamber (5) is open, two interfaces at the lower part of the oil sample buffer chamber are respectively connected with two ports of the U-shaped oscillation tube (1) through pipelines, and a third valve (13) and a fourth valve (14) are respectively arranged on the pipelines; first temperature sensor (7) set up on the inside lateral wall of accuse temperature heat preservation (10), second temperature sensor (8) set up on the outside lateral wall of accuse temperature heat preservation (10), third temperature sensor (9) set up between two standpipes of U type oscillating pipe (1).
2. The transformer oil gas content testing device for measuring density by the U-shaped oscillating tube according to claim 1, wherein a left top port and a right top port of the U-shaped oscillating tube (1) are respectively connected with an input medium pipeline and an output medium pipeline through hard silicone tubes.
3. The transformer oil gas content testing device for measuring the density by the U-shaped oscillation tube as claimed in claim 1, wherein the absolute residual pressure of the vacuum pump (6) is not more than 10 Pa.
4. The transformer oil gas content testing device for measuring the density by the U-shaped oscillating tube according to claim 1, wherein the measurement accuracy of the first temperature sensor (7), the second temperature sensor (8) and the third temperature sensor (9) is +/-0.1 ℃, and the temperature control accuracy of the temperature control insulating layer (10) is +/-0.1 ℃.
5. A method applied to the transformer oil gas content testing device for measuring the density by the U-shaped oscillating tube according to any one of claims 1 to 4, is characterized by comprising the following steps:
s101, calibrating the device; calibrating the U-shaped oscillation tube (1) by respectively adopting clean air and pure water as standard substances, and calculating an instrument constant F of the U-shaped oscillation tube (1);
s102, measuring the density of the oil sample to be measured; the method comprises the steps that the U-shaped oscillation tube (1) is washed by using an oil sample to be detected, and after the oil sample to be detected in the U-shaped oscillation tube (1) is free of bubbles and the temperature reaches a set value and is stable, the density rho of the oil sample to be detected is calculated0；
S103, measuring the density of the oil sample to be measured after vacuum degassing; carrying out vacuum degassing treatment on the oil sample to be detected in the U-shaped oscillation pipe (1) by using a vacuum pump (6), slowly removing dissolved gas in the oil sample to be detected, measuring the degassed oil sample in the U-shaped oscillation pipe (1) after degassing is finished, and calculating the density rho of the oil sample to be detected after vacuum degassing1；
S104, calculating the gas content in the oil sample to be measured; according to rho0、ρ1、ρQi (Qi)And U-shaped oscillation tube volume V0And calculating to obtain the volume V of the gas content of the oil sample to be measuredQi (Qi)And calculating the gas content G of the oil sample to be measured.
6. The method for testing the gas content of the transformer oil for measuring the density of the U-shaped oscillating tube according to claim 5, wherein the calibration process of the U-shaped oscillating tube (1) by using clean air as a standard substance in the step S101 comprises the following steps: before starting testing, all valves are in a closed state, at the moment, a first valve (11) and a second valve (12) are opened, clean air is introduced into the device from the first valve (11), the U-shaped oscillation pipe (1) is swept for not less than 10min, the first valve (11) and the second valve (12) are closed successively, the temperature control function is started through a temperature control heat insulation layer (10), after the temperatures of a first temperature sensor (7), a second temperature sensor (8) and a third temperature sensor (9) are stabilized at 20 +/-0.1 ℃, the testing function of the device is started, a magnet (2) is enabled to generate oscillation with fixed frequency through an electronic excitation oscillator (3), and the oscillation period T is recorded through a frequency counter (17) and the third temperature sensor (9)AAnd temperature tAAfter that, the test is ended.
7. The method for testing the gas content of the transformer oil for measuring the density of the U-shaped oscillating tube according to claim 6, wherein the step S101 of calibrating the U-shaped oscillating tube (1) by using pure water as a standard substance comprises the following steps: all valves are in a closed state before testing, a first valve (11) and a second valve (12) are opened, pure water enters a U-shaped oscillating pipe (1) through the first valve (11) and is discharged from the second valve (12), the U-shaped oscillating pipe (1) and a pipeline are washed for 3-5 min by the pure water, after no bubbles exist in the U-shaped oscillating pipe (1) and the pipeline, the first valve (11) and the second valve (12) are closed successively, a temperature control function is started through a temperature control heat insulation layer (10), after the temperatures of a first temperature sensor (7), a second temperature sensor (8) and a third temperature sensor (9) are stabilized at 20 +/-0.1 ℃, a testing function of a device is started, and after the temperatures of the first temperature sensor (7), the second temperature sensor (8) and the third temperature sensor (9)An electronically excited oscillator (3) causes the magnet (2) to oscillate at a fixed frequency, the oscillation period T being recorded by means of a frequency counter (17) and a third temperature sensor (9)WAnd temperature tW(ii) a After the process is finished, pure water in the U-shaped oscillation pipe (1) is discharged, the first valve (11) and the second valve (12) are opened, then dry clean air is introduced from the first valve (11) to blow the U-shaped oscillation pipe (1) and corresponding pipelines dry, and then all the valves are closed.
8. The method for testing the gas content of the transformer oil by using the U-shaped oscillation tube for measuring the density as claimed in claim 5, wherein the process of measuring the density of the oil sample to be measured in the step S102 is as follows: before the test is started, all valves are in a closed state, a first valve (11) and a second valve (12) are opened, an oil sample to be tested enters a U-shaped oscillation tube (1), the U-shaped oscillation tube (1) is flushed for 3-5 min by the oil sample to be tested, then a third valve (13), a fourth valve (14) and a fifth valve (15) are opened, the second valve (12) is closed, the oil sample to be tested enters an oil sample buffer chamber (5) from the third valve (13) and the fourth valve (14) to be flushed, and the flushed oil sample is discharged through the fifth valve (15); when an oil sample to be tested is filled with the U-shaped oscillation pipe (1), the oil sample buffer chamber (5) and the corresponding pipeline and no air bubble exists in oil, the first valve (11), the third valve (13), the fourth valve (14) and the fifth valve (15) are closed, the temperature control function is started through the temperature control heat preservation layer (10), the first temperature sensor (7), the second temperature sensor (8) and the third temperature sensor (9) are stabilized at 20 +/-0.1 ℃, the test function of the device is started, the magnet (2) is enabled to generate oscillation with fixed frequency through the electronic excitation oscillator (3), and the oscillation period T is recorded through the frequency counter (17) and the third temperature sensor (9)0And temperature t0。
9. The method for testing the gas content of the transformer oil for measuring the density by using the U-shaped oscillation tube as claimed in claim 5, wherein the process of measuring the density of the oil sample to be measured after vacuum degassing in the step S103 is as follows: opening a third valve (13), a fourth valve (14) and a sixth valve (16), opening a vacuum pump (6), vacuumizing and degassing the oil sample, and keeping the vacuum degree at-0.05Mpa, pumping for 10min, adjusting the vacuum degree to-0.1 Mpa, continuing pumping for 20min, closing the vacuum pump (6) and the sixth valve (16), starting the temperature control function through the temperature control heat preservation layer (10), starting the test function of the device after the temperatures of the first temperature sensor (7), the second temperature sensor (8) and the third temperature sensor (9) are stabilized at 20 +/-0.1 ℃, exciting the oscillator (3) through electrons to enable the magnet (2) to generate oscillation with fixed frequency, and recording the oscillation period T through the frequency counter (17) and the third temperature sensor (9)1And temperature t1And after the test is finished, opening a fifth valve (15), balancing the pressure of the vacuum degassing chamber (4) to the atmospheric pressure, opening the first valve (11) and the second valve (12), and discharging the oil sample in the U-shaped oscillation tube (1).
10. The method for testing the gas content of the transformer oil for measuring the density by the U-shaped oscillating tube according to claim 5, wherein the calculation formula of the instrument constant F is as follows:
in the formula: rhoWDenotes the density, ρ, of pure water at the test temperatureARepresents the density of clean air at the test temperature; t isWRepresenting the vibration period observed when pure water is in the U-shaped oscillation tube; t isAShowing the vibration period observed when clean air is present in the U-shaped oscillating duct.
11. The method for testing the gas content of the transformer oil for measuring the density by the U-shaped oscillating tube as claimed in claim 5, wherein the density p of the oil sample to be measured is calculated in step S1020The formula of (1) is:
in the formula, T0Showing the vibration period observed by the oil sample to be measured before vacuum degassing in the U-shaped oscillation tube.
12. The method for testing the gas content of the transformer oil for measuring the density by the U-shaped oscillating tube as claimed in claim 5, wherein the density p of the oil sample to be tested after vacuum degassing is calculated in step S1031The formula of (1) is:
in the formula, T1The vibration period observed for the oil sample to be measured after vacuum degassing in the U-shaped oscillation tube is shown.
13. The method for testing the gas content of transformer oil for measuring the density by using the U-shaped oscillating tube as claimed in claim 5, wherein the gas content volume V of the oil sample to be tested is calculated in the step S104Qi (Qi)The formula of (1) is:
ρ1V0-ρ0V0＝ρqi (Qi)VQi (Qi)
In the formula, ρQi (Qi)Indicating the density, V, of the gas contained in the oil sample to be measured0Indicating volume, V, of U-shaped oscillating tubeQi (Qi)Representing the volume occupied by the gas in the oil sample to be measured.
14. The method for testing the gas content of the transformer oil for measuring the density by the U-shaped oscillating tube according to claim 5, wherein the formula for calculating the gas content G of the oil to be measured in the step S104 is as follows:
wherein t represents the constant temperature of the test apparatus, and 0.0008 represents the thermal expansion coefficient of the oil, in units of 1/DEG C.
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