阅读说明：本技术 振动与电场作用对油中特征气体影响的研究装置及方法 (Device and method for researching influence of vibration and electric field action on characteristic gas in oil ) 是由 吴杰 尹睿涵 吴兴旺 丁国成 柯艳国 谢佳 朱太云 杨海涛 张晨晨 张乔根 文韬 于 2021-08-09 设计创作，主要内容包括：本发明公开了一种振动与电场作用对油中特征气体影响的研究装置及方法,装置包括一个测定池,在测定池底部固定设置压电陶瓷换能器,在测定池顶部之上通过支架设置有激光位移传感器,测定池中在激光位移传感器聚焦压电陶瓷换能器的聚焦线两侧相对设置有一对电极板,两个电极板分别设置有连接臂,两个连接臂分别从测定池两侧侧壁伸出连接试验电压,其中,一个连接臂当中设置有微分头,微分头用于调节两个电极板之间的距离用以改变两个电极板之间在施加电压时的电场强度,所述激光位移传感器的输出连接信号处理器,一个色谱仪通过获取测定池中的样品油与测定池连接,一个信号发生器的输出通过可调节功率放大器连接超声换能器。(The invention discloses a device and a method for researching the influence of vibration and electric field action on characteristic gas in oil, the device comprises a measuring cell, a piezoelectric ceramic transducer is fixedly arranged at the bottom of the measuring cell, a laser displacement sensor is arranged on the top of the measuring cell through a bracket, a pair of electrode plates are oppositely arranged at two sides of a focusing line of the laser displacement sensor focusing piezoelectric ceramic transducer in the measuring cell, the two electrode plates are respectively provided with a connecting arm, the two connecting arms respectively extend out from the side walls at two sides of the measuring cell to be connected with test voltage, wherein a differential head is arranged in one connecting arm and used for adjusting the distance between the two electrode plates so as to change the electric field intensity between the two electrode plates when the voltage is applied, the output of the laser displacement sensor is connected with a signal processor, a chromatograph is connected with the measuring cell by obtaining sample oil in the measuring cell, the output of a signal generator is connected to the ultrasonic transducer through an adjustable power amplifier.)

1. A device for researching the influence of vibration and electric field action on characteristic gas in oil is characterized by comprising a measuring cell, wherein the measuring cell is used for putting transformer sample oil into the measuring cell during research, a piezoelectric ceramic transducer is fixedly arranged at the bottom of the measuring cell, a laser displacement sensor is arranged on the top of the measuring cell through a support, the laser displacement sensor focuses on the vibration output of the piezoelectric ceramic transducer, a pair of electrode plates are oppositely arranged on two sides of a focusing line of the piezoelectric ceramic transducer focused by the laser displacement sensor in the measuring cell, two oppositely arranged electrode plates are respectively provided with connecting arms, the two connecting arms respectively extend out of the side walls of the two sides of the measuring cell to connect test voltage, a differential head is arranged in one connecting arm and used for adjusting the distance between the two electrode plates so as to change the electric field intensity between the two electrode plates during voltage application, the output of the laser displacement sensor is connected with the signal processor, a chromatograph is connected with the measuring cell by obtaining sample oil in the measuring cell, and the output of the signal generator is connected with the ultrasonic transducer by the adjustable power amplifier.

2. The research device of claim 1, wherein the resonant frequency of the piezoelectric ceramic transducer is 25.6kHz, and the adjustment range of the power amplifier is 0-20W.

3. The apparatus of claim 1, wherein the sample cell is a cuboid having a length of 220mm, a width of 220mm, and a height of 300 mm.

4. The investigation apparatus according to claim 1, wherein the parameters of the laser displacement sensor are selected as follows: the laser wavelength is 632.8nm, the frequency range is DC-3 MHz, and the displacement resolution is 15 pm.

5. The apparatus of claim 1, wherein the chromatograph is configured to obtain the sample oil in the measurement cell on-line via a connection to an inlet/outlet of the measurement cell.

6. A method for investigating the effect of vibration and electric field on a characteristic gas in oil, comprising the investigation apparatus according to claim 1, characterized in that the method comprises the steps of:

step 1: determining an input test voltage, namely adjusting the test voltage between the two electrode plates to the maximum electric field without breaking down sample oil, adjusting the output power of the power amplifier from low to high step by using the fixed resonant frequency of the piezoelectric ceramic transducer under the conditions that the measuring cell is an empty cell and no test voltage is applied, increasing the displacement variation amplitude output by the piezoelectric ceramic transducer, acquiring the displacement variation amplitude value through a laser displacement sensor, and establishing a relation table between the output power of the power amplifier and the output displacement variation amplitude of the piezoelectric ceramic transducer;

step 2: putting the transformer sample oil into a measuring cell, adjusting the output power of a power amplifier step by step from low to high according to a relational table to increase the displacement change amplitude value output by a piezoelectric ceramic transducer, converting the displacement change amplitude value to calculate the pressure change amplitude value of the sample oil, and synchronously monitoring characteristic gas of gas content change in the sample oil step by a chromatograph;

and step 3: when the characteristic gas appears, the input voltage of an electric field is accessed, the differential head is adjusted to change the electric field intensity in the action range of the piezoelectric ceramic transducer, and the influence rule of three factors of the electric field intensity, the pressure change amplitude and the action time on the characteristic gas in the oil is researched;

and 4, step 4: and obtaining the characteristic gas change rule corresponding to the pressure change amplitude and the electric field from the obtained characteristic gas data by using a David triangle.

7. The method according to claim 6, wherein the pressure change amplitude of the sample oil is calculated by converting the displacement change amplitude value: is to bring the displacement variation amplitude value into the pressure variation amplitude value of the sample oil obtained in the CFD analysis.

8. The method according to claim 7, wherein the CFD analysis is to establish a vibration model of the piezoelectric ceramic transducer with the fixed wall surface of the measuring cell as a boundary condition, form a flow field pressure distribution cloud map of the vibration surface at the time of the minimum pressure and the maximum pressure in each vibration period according to the piezoelectric ceramic spherical focusing vibration in the model, extract the pressure change amplitude from the distribution cloud map, obtain different pressure change amplitudes according to different displacement change amplitude values, and further form the relationship between the displacement change amplitude and the pressure change amplitude.

9. The method according to claim 8, wherein the sample cell is a cuboid with a length of 220mm, a width of 220mm and a height of 300mm, the diameter of the electrode plate is 40mm, the distance between the two electrode plates is adjusted to be 1-4 mm, the electric field value is adjusted to be 0-20 kV/mm, the adjustment range of the power amplifier is 0-20W, and the output power of the power amplifier is adjusted step by step from low to high: the output power of the power amplifier is incremented in 0.5W steps.

10. The method according to claim 9, wherein the characteristic gas has a gas content of 2.1%, an electric field strength of 2KV/mm, a vibration time of 3 hours, vibration powers of 2W, 4W, 6W, 8W, 10W, 12W, corresponding displacement change amplitude values of 0.048 μm, 0.097 μm, 0.151 μm, 0.205 μm, 0.247 μm, 0.298 μm, corresponding pressure change amplitudes of 24668Pa, 50159Pa, 77156Pa, 101356Pa, 125659Pa, 151365Pa, and a pressure change amplitude value for bringing the pressure change amplitude value into a great triangle to obtain a cavitation threshold value is 101356 Pa.

Technical Field

The invention belongs to the technical field of liquid insulating materials of electrical equipment, and particularly relates to a device and a method for researching influence of vibration and electric field action on characteristic gas in oil.

Background

The oil-immersed power transformer is a core device in a power system, and the reliable operation of the oil-immersed power transformer is crucial to the safety and stability of the power system. The insulation state of the oil paper needs to be monitored in real time, Dissolved Gas Analysis (DGA) is a common monitoring and analyzing means, the type of the fault is determined according to different gas production characteristics corresponding to different faults in the oil paper, and the currently obtained corresponding relation between the fault type and the characteristic gas mainly comprises various overheating faults and discharge faults. However, in the existing power system, the increase of characteristic gas (such as acetylene) corresponding to the detected discharge fault often occurs, and the discharge signal is not detected on site, so that the analysis result is misled. Therefore, characteristic gas similar to the discharge fault is generated due to the fact that certain fault types or certain abnormal working conditions exist in the oil paper insulation system, and further analysis results of the on-site oil chromatography are induced, so that misjudgment is caused, and unnecessary waste in the aspects of economy, manpower and material resources is brought.

Research has proved that high-frequency vibration in the transformer oil can cause cavitation bubbles to be generated, and the local high-temperature and high-pressure effect generated when the cavitation bubbles are broken causes the oil to be decomposed to generate various characteristic gases. In actual transformer oil, the electric field and vibration simultaneously exist, and the existence of the electric field influences the strength of the cavitation effect. Therefore, the condition of the characteristic gas generated by the combined action of the electric field and the vibration is more complicated, so that the influence rule of the electric field and the vibration on the characteristic gas in the oil is necessarily researched, the change mode of the content of the characteristic gas under the electric field and the vibration is found, and the practice of oil chromatographic analysis is better guided. However, at present, no research on the aspect is carried out at home and abroad, so that the practice of better guiding the oil chromatographic analysis by researching the influence rule of the combined action of the electric field and the vibration on the characteristic gas in the oil becomes a problem to be solved at present.

Disclosure of Invention

The invention aims to provide a device and a method for researching the influence of vibration and electric field action on characteristic gas in oil, which solve the problem of the corresponding relation between the change of the characteristic gas in the oil and the vibration and the electric field and can obtain the pressure change amplitude caused by the vibration and the characteristic gas change rule under the electric field; the obtained research result is beneficial to guiding the monitoring of the insulation state of the transformer.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a device for researching the influence of vibration and electric field on characteristic gas in oil comprises a measuring cell, a transformer sample oil is placed in the measuring cell during research, a piezoelectric ceramic transducer is fixedly arranged at the bottom of the measuring cell, a laser displacement sensor is arranged on the top of the measuring cell through a support, the laser displacement sensor focuses on the vibration output of the piezoelectric ceramic transducer, a pair of electrode plates are oppositely arranged on two sides of a focal line of the laser displacement sensor focused piezoelectric ceramic transducer in the measuring cell, connecting arms are respectively arranged on the two oppositely arranged electrode plates, the two connecting arms respectively extend out of the side walls on two sides of the measuring cell to be connected with test voltage, a differential head is arranged in one connecting arm and used for adjusting the distance between the two electrode plates so as to change the electric field intensity between the two electrode plates when the voltage is applied, the output of the laser displacement sensor is connected with the signal processor, a chromatograph is connected with the measuring cell by obtaining sample oil in the measuring cell, and the output of the signal generator is connected with the ultrasonic transducer by the adjustable power amplifier.

The scheme is further as follows: the resonant frequency of the piezoelectric ceramic transducer is 25.6kHz, and the adjusting range of the power amplifier is 0-20W.

The scheme is further as follows: the sample cell is a cuboid with the length of 220mm, the width of 220mm and the height of 300 mm.

The scheme is further as follows: the parameters of the laser displacement sensor are selected as follows: the laser wavelength is 632.8nm, the frequency range is DC-3 MHz, and the displacement resolution is 15 pm.

The scheme is further as follows: and the chromatograph is connected with an inlet and outlet pipeline of the measuring cell to obtain the sample oil in the measuring cell on line.

A method for researching the influence of vibration and electric field action on the characteristic gas in the oil is based on the method for researching the influence of vibration and electric field action on the characteristic gas in the oil, wherein the method comprises the following steps: .

Step 1: determining an input test voltage, namely adjusting the test voltage between the two electrode plates to the maximum electric field without breaking down sample oil, adjusting the output power of the power amplifier from low to high step by using the fixed resonant frequency of the piezoelectric ceramic transducer under the conditions that the measuring cell is an empty cell and no test voltage is applied, increasing the displacement variation amplitude output by the piezoelectric ceramic transducer, acquiring the displacement variation amplitude value through a laser displacement sensor, and establishing a relation table between the output power of the power amplifier and the output displacement variation amplitude of the piezoelectric ceramic transducer;

step 2: putting the transformer sample oil into a measuring cell, adjusting the output power of a power amplifier step by step from low to high according to a relational table to increase the displacement change amplitude value output by a piezoelectric ceramic transducer, converting the displacement change amplitude value to calculate the pressure change amplitude value of the sample oil, and synchronously monitoring characteristic gas of gas content change in the sample oil step by a chromatograph;

and step 3: when the characteristic gas appears, the input voltage of an electric field is accessed, the differential head is adjusted to change the electric field intensity in the action range of the piezoelectric ceramic transducer, and the influence rule of three factors of the electric field intensity, the pressure change amplitude and the action time on the characteristic gas in the oil is researched;

and 4, step 4: and obtaining the characteristic gas change rule corresponding to the pressure change amplitude and the electric field from the obtained characteristic gas data by using a David triangle.

The scheme is further as follows: and calculating the pressure change amplitude of the sample oil by the displacement change amplitude value conversion: is to bring the displacement variation amplitude value into the pressure variation amplitude value of the sample oil obtained in the CFD analysis.

The scheme is further as follows: the CFD analysis is to establish a vibration model of the piezoelectric ceramic transducer with the fixed wall surface of the measuring cell as a boundary condition, form a flow field pressure distribution cloud chart of the vibration surface at the moment of minimum pressure and maximum pressure in each vibration period according to piezoelectric ceramic spherical focusing vibration in the model, extract a pressure change amplitude from the distribution cloud chart, obtain different pressure change amplitudes according to different displacement change amplitudes, and further form the relationship between the displacement change amplitude and the pressure change amplitude.

The scheme is further as follows: the sample cell is the cuboid of long 220mm, wide 220mm, height 300mm, the electrode plate diameter is 40mm, and two plate electrode interval control range are 1~4mm, and the electric field value scope is 0~20kV/mm, power amplifier's control range is 0~20W, adjust power amplifier's output from low to high step by step: the output power of the power amplifier is incremented in 0.5W steps.

The scheme is further as follows: the gas content of the characteristic gas is 2.1%, the electric field intensity is 2KV/mm, the vibration time is 3 hours, the vibration power is 2W, 4W, 6W, 8W, 10W and 12W respectively, the corresponding displacement change amplitude values are 0.048 μm, 0.097 μm, 0.151 μm, 0.205 μm, 0.247 μm and 0.298 μm respectively, the corresponding pressure change amplitude values are 24668Pa, 50159Pa, 77156Pa, 101356Pa, 125659Pa and 151365Pa, and the pressure change amplitude value is substituted into a large satellite triangle to obtain the cavitation threshold value is 101356 Pa.

The invention has the beneficial effects that: the change rule of the characteristic gas in the oil under the combined action of the vibration and the electric field can be revealed by the pioneering combination of numerical calculation and experimental analysis, and the pressure change amplitude caused by the vibration and the change rule of the characteristic gas in the electric field can be obtained by researching the method for researching the characteristic gas in the oil under the action of the vibration and the electric field. The obtained research result is beneficial to guiding the monitoring of the insulation state of the transformer.

The invention is described in further detail below with reference to the figures and examples.

Drawings

FIG. 1 is a schematic view of the apparatus of the present invention;

FIG. 2 is a diagram of a CFD analysis model according to the present invention;

FIG. 3 is a cloud diagram of the pressure distribution of the focusing vibration flow field of the piezoelectric ceramic sphere according to the present invention;

FIG. 4 is a focused vibration physical model of the piezoelectric ceramic sphere of the present invention;

FIG. 5 is a schematic diagram of the spherical radius vibration parameters of the piezoelectric ceramic of the present invention;

FIG. 6 is a schematic view of a grand satellite;

FIG. 7 is a schematic diagram of a grand satellite triangle with an example of an inbound parameter.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

In the description of the present embodiment, it should be noted that the terms "connected" and "disposed" should be interpreted broadly, for example, the "connection" may be a wire connection or a mechanical connection; the 'placing' can be fixedly connected placing or integrally formed placing. The specific meanings of the above terms in the present embodiment can be understood by those of ordinary skill in the art according to specific situations.

The utility model provides a vibration and electric field effect are to research device of characteristic gas influence in oil, as shown in figure 1, the device includes a survey cell 1, puts into transformer sample oil when the survey cell is used for the research, puts into transformer sample oil when the survey cell is used for the survey, for reduce the survey oil mass as far as, the sample cell is the cuboid of 220mm long, 220mm wide, 300mm high. The piezoelectric ceramic transducer 2 is fixedly arranged at the bottom of the measuring cell, and the piezoelectric ceramic transducer with the resonant frequency of 25.6kHz is used in the embodiment; the output of one signal generator 3 is connected with the piezoelectric ceramic transducer 2 through an adjustable power amplifier 4, and the adjusting range of the power amplifier is 0-20W. The device is characterized in that a laser displacement sensor 5 is arranged on the top of a measuring cell 1 through a support, the laser displacement sensor 5 focuses the vibration output of a piezoelectric ceramic transducer 2, a pair of electrode plates 7 are oppositely arranged on two sides of a focusing line 6 of the laser displacement sensor focusing piezoelectric ceramic transducer in the measuring cell, connecting arms 8 are respectively arranged on the two oppositely arranged electrode plates, the two connecting arms respectively extend out of the side walls of the two sides of the measuring cell to be connected with a test voltage 9, wherein a differential head 10 is arranged in one connecting arm, the differential head 10 is arranged in the connecting arm at one end of the grounding side of the test voltage, the differential head is used for adjusting the distance between the two electrode plates to change the electric field intensity between the two electrode plates when the voltage is applied, the output of the laser displacement sensor 5 is connected with a signal processor 11, and the signal processor 5 carries out CFD analysis on the obtained laser displacement sensor signal to obtain a pressure amplitude value, a chromatograph 12 is connected to the measuring cell by obtaining the sample oil in the measuring cell, which can be extracted from the sample oil by a laboratory instrument at each measurement, or can be connected to the measuring cell on-line by connecting to the inlet and outlet pipes of the measuring cell.

The research on the influence of vibration and electric field action on the characteristic gas in the oil can be realized through the structure of the research device and the selected index parameters.

Therefore, when the output power is adjusted to increase the displacement change amplitude output by the piezoelectric ceramic transducer, voltage is applied to the two electrode plates to provide a uniform electric field; adjusting the electrode spacing by using a differential head to adjust an electric field between the two electrode plates; the single-point laser displacement sensor measures the vibration displacement of different transducers under different powers; measuring the change of the characteristic gas content in the oil sample by oil chromatographic analysis; the CFD analysis of the transducer displacement and the pressure conversion in the oil obtains the change amplitude of the pressure in the oil under different displacements of the transducer in a simulation mode, and finally the data can be used for researching the influence of vibration and electric field action on the characteristic gas in the oil.

The method of investigation comprises the following steps: .

Step 1: determining an input test voltage, namely adjusting the test voltage between the two electrode plates to the maximum electric field without breaking down sample oil, adjusting the output power of the power amplifier from low to high step by using the fixed resonant frequency of the piezoelectric ceramic transducer under the conditions that the measuring cell is an empty cell and no test voltage is applied, increasing the displacement variation amplitude output by the piezoelectric ceramic transducer, acquiring the displacement variation amplitude value through a laser displacement sensor, and establishing a relation table between the output power of the power amplifier and the output displacement variation amplitude of the piezoelectric ceramic transducer;

step 2: putting the transformer sample oil into a measuring cell, adjusting the output power of a power amplifier step by step from low to high according to a relational table to increase the displacement change amplitude value output by a piezoelectric ceramic transducer, converting the displacement change amplitude value to calculate the pressure change amplitude value of the sample oil, and synchronously monitoring characteristic gas of gas content change in the sample oil step by a chromatograph;

and step 3: when the characteristic gas appears, the input voltage of an electric field is accessed, the differential head is adjusted to change the electric field intensity in the action range of the piezoelectric ceramic transducer, and the influence rule of three factors of the electric field intensity, the pressure change amplitude and the action time on the characteristic gas in the oil is researched;

and 4, step 4: and obtaining the characteristic gas change rule corresponding to the pressure change amplitude and the electric field from the obtained characteristic gas data by using a David triangle.

Wherein: and calculating the pressure change amplitude of the sample oil by the displacement change amplitude value conversion: the displacement change amplitude value is substituted into the CFD analysis to obtain the pressure change amplitude value of the sample oil.

Wherein: the step-by-step adjustment of the output power of the power amplifier from low to high is realized by increasing the displacement change amplitude of the output of the piezoelectric ceramic transducer in an incremental adjustment of 0.5 watt power output in a period of time; the time period is 10 minutes under the condition that the sample cell is a rectangular parallelepiped having a length of 220mm, a width of 220mm, and a height of 300 mm; the adjusting range of the distance between the two electrode plates is 1-4 mm, the value range of an electric field is 0-20 kV/mm, and the adjusting range of the power amplifier is 0-20W.

The CFD analysis is as shown in FIG. 2, and is to establish a vibration model of a piezoelectric ceramic transducer with BC, CD, DE, FG, GH, HA measuring cell fixed wall as boundary conditions, wherein: AB is a pressure inlet boundary, EF is a vibration boundary, focusing vibration is carried out on the model according to the piezoelectric ceramic spherical surface EF which is the vibration boundary, a flow field pressure distribution cloud chart at the moment of the minimum and maximum values of the vibration surface pressure shown in figure 3 is formed by displacement change amplitude values in each vibration period according to the focusing vibration of the piezoelectric ceramic spherical surface in the model, pressure change amplitude values are extracted from the distribution cloud chart, different pressure change amplitude values are obtained according to different displacement change amplitude values, and then the relation between the displacement change amplitude values and the pressure change amplitude values is formed.

The periodic vibration can cause the pressure in the oil to change periodically, and simulation results show that the pressure of the whole flow field changes along with the periodic vibration, and fig. 3 is a flow field pressure distribution cloud chart at the moment of minimum and maximum pressure of a vibration surface. It can be found that the pressure is emitted from the center of the vibration surface to the periphery, the pressure change near the most center of the vibration surface is most obvious, the area is the area where the cavitation is firstly developed, and then a pressure probe is placed in the flow field to capture the space and time points of the maximum and minimum pressure, and the pressure change amplitude is obtained. FIG. 3 is a cloud chart showing the pressure change of the flow field under the condition that the displacement at the center of the vibrating surface EF is 0.2 μm when the gas content is increased and changed, and the maximum pressure change amplitude obtained by extraction is 101275 Pa. As to how to obtain the pressure Pa from the vibration displacement μm: the calculation belongs to single-phase fluid-solid coupling calculation, namely, the change of the position of a solid in liquid can cause the change of a flow field in the liquid, and variables describing the flow field mainly comprise flow rate, pressure, Reynolds number and the like, namely, only boundary conditions are set in fluent, and parameters such as the pressure and the like can be obtained through calculation.

Wherein the formation of the cloud map can be obtained by the following analysis: the spherical focusing vibration is the real condition of the piezoelectric ceramic surface vibration of the ultrasonic transducer, and a physical model close to the real condition can be obtained by simulating the vibration mode. As shown in fig. 4, a solid line in the middle of the three arcs is the initial position of the vibration plane, which is a spherical surface with a focus point, and the focus point is indicated by two upwardly intersecting dotted lines. The periphery of the vibration surface is fixed. In this vibration mode, forward and backward vibrations, the vibration surface is spherical, and only the position of the focal point and the focal length are changed. As shown in fig. 5, R0 is the spherical radius of the initial equilibrium position, which is determined by the transducer fabrication process, with the center of the sphere at the origin of coordinates. R1 is the radius of the sphere when vibrated to the top, with its center somewhere above the origin (0, -l 1); r2 is the radius of the spherical surface when vibrated to the lowermost position, and its center of sphere is somewhere below the origin (0, l2), and will now be described with respect to a two-dimensional cross section.

The three circles intersect at two points M and N, and R2 can be easily determined according to the geometric relationship<R0<And R1. The opening angle of a cross-section fan formed by connecting the MON three points is theta, so that the coordinates of M and N are respectively thetaAnd

we are concerned with the change between points M, N, i.e. withThe distribution of y in this closed interval (i.e. the above-mentioned pressure change cloud chart) needs to be derived to obtain the amplitude of the inner circle surface in this interval, i.e. the distance Δ y between two of three circles₁＝y₀-y₁，△y₂＝y₂-y₀。

The equations of the three circles are respectively

x²+(y+l₁)²＝R₁ ² (1)

x²+y²＝R₀ ² (2)

x²+(y-l₂)²＝R₂ ² (3)

The coordinates of the M point and the N point are respectively substituted into equations (1) and (3), so that the circle center deviation amounts l1 and l2 of two circles R1 and R2 can be obtained:

the ordinate of the circles R1 and R2 are:

substituting equations (4) and (5) into the above equations yields detailed expressions for the ordinate of circles R1 and R2 as:

thus, the distance between the three circles can be deduced:

wherein

When the actual ultrasonic transducer works, a nominal resonant frequency exists, and simultaneously, a plurality of resonant frequencies exist, so that the vibration condition is complex. The output of the power amplifier of the driving transducer of the present embodiment is a sinusoidal signal with a single frequency, so the vibration mode is a simple harmonic vibration at the resonance frequency. Thus simplifying a spherical focusing vibratory surface to a simple harmonic vibration near the equilibrium position, the position function describing the vibratory surface can be expressed as:

in the UDF function for actually writing a vibration surface, R1 and R2 are unknowns (because the spherical radius of the vibration surface is not known), and the vibration amplitude a₀＝△y_1max＝△y_2maxGiven the known quantities, (x ═ 0) the values of R1 and R2 were obtained by inverting equations (1) and (3) and substituting into the position function (12). This embodiment uses an ultrasonic transducer of type HS-8SH-3825 with a radius of 150mm at the equilibrium position, a diameter of the vibrating surface of 58mm, and a resonant frequency of 25 + -0.8 kHz.

Building a calculation model and analyzing results: the simulation of the vibration surface is mainly realized by fluent software and a self-contained UDF (Universal description framework), and a corresponding two-dimensional simulation model is established according to an experimental platform structure, wherein BC, CD, DE, FG, GH and HA are set as fixed wall surface boundary conditions, AB is set as a pressure inlet boundary, EF is set as a vibration boundary, and the vibration mode is spherical focusing vibration and serves as a pressure change source. Because the maximum displacement of the vibration surface does not exceed 1 mu m in the simulation process, the grids near the vibration surface are locally encrypted, and the numerical calculation precision is ensured. A dynamic grid setting mode combining diffusion and spring fairing is adopted, the vibration of a vibration surface is simulated by a UDF function, and a time period is divided into 400 time steps for simulation.

In the examples: the characteristic gas refers to gas obtained by analyzing sample oil by chromatograph, and specifically comprises CO and CO₂、H₂、CH₄、C₂H₆、C₂H₄、C₂H₂. In which CH₄、C₂H₂、C₂H₄The percentage contents of the three hydrocarbon gases for judging the fault type of the transformer oil form a large-guard triangle as shown in fig. 6, and the fault types represented by different areas in the large-guard triangle are as follows: PD-partial discharge, D1-Low energy discharge, D2-high energy discharge, T1-thermal failure, T<300 ℃; t2-thermal failure, 300 deg.C<t<700 ℃; t3-thermal failure, T>700℃。

Triangle in C₂H₂、C₂H₄、CH₄The proportion is as follows:

in the formula:

x is C₂H₂The content of (a), mu L/L;

y is C₂H₄The content of (a), mu L/L;

z is CH₄The content of (a), mu L/L;

the limiting regions in FIG. 6 are shown in Table 1

TABLE 1 regional limits

PD	98％CH4
					D1	23％C2H4	13％C2H2
D2	23％C2H4	13％C2H2	38％C2H4	29％C2H2
					T1	4％C2H2	10％C2H4
T2	4％C2H2	10C2H4	50％C2H4
					T3	15％C2H2	50％C2H4

The following is a specific example: the gas content of the characteristic gas is 2.1%, the electric field intensity is 2KV/mm, the vibration time is 3 hours, the vibration power is 2W, 4W, 6W, 8W, 10W and 12W respectively, the corresponding displacement change amplitude values are 0.048 μm, 0.097 μm, 0.151 μm, 0.205 μm, 0.247 μm and 0.298 μm respectively, the corresponding pressure change amplitude values are 24668Pa, 50159Pa, 77156Pa, 101356Pa, 125659Pa and 151365Pa respectively, the C2H2, C2H4 and CH4 data under six conditions are substituted into a large triangle through the method, and the obtained result is shown as a circle point marked in 7, and the pressure change amplitude value of the cavitation threshold value can be judged to be 101356 Pa.

As can be seen from FIG. 7, as the vibration amplitude increases, the pressure change amplitude in the oil increases, the cavitation phenomenon of the oil gradually increases from beginning to beginning, and T1-T2-T3 in the great-duty triangle all fall in the superheat region. The state of the oil, the electric field intensity and the vibration intensity are changed to obtain a large-sanitary triangle under different states.

The device and the method are creatively combined with numerical calculation and experimental analysis, the change rule of the characteristic gas in the oil under the combined action of the over-vibration and the electric field is disclosed, and the pressure change amplitude caused by the vibration and the change rule of the characteristic gas in the electric field can be obtained by researching the research method of the characteristic gas in the oil under the action of the vibration and the electric field. The obtained research result is beneficial to guiding the monitoring of the insulation state of the transformer.