Method and system for detecting oil level of oil-immersed transformer bushing

Abstract

According to the method and system for detecting the oil level of the oil-immersed transformer bushing, an upper computer adopts a simulation method to determine the installation position, the transmitting power and the transmitting frequency of an ultrasonic probe in a detection device, determines effective echo signals from n times of echo signals, and determines the propagation duration of the effective echo signals when no oil exists in the bushing and when oil exists in the bushing; fixing the detection device on the side wall of the sleeve according to the mounting position of the ultrasonic probe; the upper computer verifies whether the current position of the ultrasonic probe is deviated from the mounting position or not; if no deviation exists, the upper computer sends a detection instruction to the detection device; when receiving the detection instruction, the detection device detects the propagation duration of an effective echo signal in the to-be-detected sleeve and uploads the propagation duration to the upper computer; the upper computer judges whether the oil level is detected or not according to the propagation duration of the effective echo signal when no oil exists in the casing and oil exists in the casing and the propagation duration of the effective echo signal in the casing to be detected; when it is judged that the oil level is detected, the upper computer outputs the oil level of the casing pipe.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent power grid equipment monitoring. Specifically, it relates to a detection method and system for the oil level of an oil-immersed transformer bushing based on ultrasonic detection technology. Background Art

[0002] As an important component of a transformer, high-voltage oil-immersed bushings have been widely used with the large-scale and high-density laying of the power grid. However, due to different construction batches, operation times, and design schemes of substations, there are significant differences in the types of transformer bushings at each station, and the observation methods of the bushing oil level also vary. Currently, the means of observing the bushing oil level in substations are relatively single. During the daily inspection of bushings, there are also problems such as large observation angles and dust accumulation in the observation holes. These factors seriously affect the real-time monitoring of the bushing oil level by operators. Once serious oil leakage occurs in the bushing, the insulation level of the transformer will be greatly affected, and the stable operation of the substation will be severely tested. Therefore, it is urgent to complete the detection of the bushing oil level through more intelligent and information-based means.

[0003] In the prior art, the method for identifying the oil level of a power transformer bushing based on infrared images has gradually become the mainstream detection method for electrical equipment faults. Utilizing the different thermal conductivity coefficients of the media in the upper and lower layers of the oil-air interface in the bushing, there will be an obvious color difference at the interface in the infrared image. Therefore, the oil level can be identified through the infrared image of the bushing. However, these methods mainly rely on manual operation using the software provided by the infrared imager manufacturer to sequentially frame the bushing part in the infrared image and mainly diagnose based on temperature information. The diagnostic results are easily affected by background noise, lacking the ability to monitor the bushing oil level in real time and unable to meet the requirements of the power system for real-time performance and accuracy. Summary of the Invention

[0004] To solve the deficiencies in the prior art, the present invention provides a mobile ultrasonic detection method and system for the oil level of an oil-immersed transformer bushing, which completes the real-time monitoring of the bushing oil level and greatly improves the real-time performance and accuracy of the bushing oil level monitoring.

[0005] The present invention adopts the following technical solutions.

[0006] The present invention proposes a detection method for the oil level of an oil-immersed transformer bushing, including: The upper computer collects the parameters of the bushing to be measured and determines the installation position of the ultrasonic probe in the detection device by using a simulation method; based on the installation position of the ultrasonic probe, the upper computer determines the transmission power and transmission frequency of the ultrasonic probe with the goal that the ultrasonic wave emitted by the ultrasonic probe can penetrate the bushing wall thickness and the ultrasonic probe can receive the echo signal. The host computer, according to the installation position, transmission power, and transmission frequency of the ultrasonic probe, uses a simulation method to determine, from secondary echo signals, the th echo that meets the detection sensitivity requirements as the effective echo signal, and determines the propagation duration of the effective echo signal when there is no oil in the casing and the propagation duration of the effective echo signal when there is oil in the casing; Fix the detection device on the side wall of the casing according to the installation position of the ultrasonic probe; the host computer verifies whether there is a deviation between the current position and the installation position of the ultrasonic probe; if there is no deviation, the host computer sends a detection instruction to the detection device; when the detection device receives the detection instruction, it detects the propagation duration of the effective echo signal in the casing to be measured and uploads it to the host computer; the host computer uses the propagation duration of the effective echo signal when there is no oil in the casing, the propagation duration of the effective echo signal when there is oil in the casing, and the propagation duration of the effective echo signal in the casing to be measured to determine whether the ultrasonic probe detects the oil level; when it is determined that the ultrasonic probe detects the oil level, the host computer outputs the oil level of the casing.

[0007] Preferably, the host computer collects the parameters of the oil-immersed transformer casing and uses a simulation method to determine the installation position of the ultrasonic probe in the detection device, including: The host computer collects the parameters of the oil-immersed transformer casings in each substation, including the manufacturer, model, maximum oil level height, internal insulating oil dielectric constant, casing porcelain wall thickness, and casing oil cavity shape parameters; using the manufacturer and model as classification labels, and using the maximum oil level height, internal insulating oil dielectric constant, casing porcelain wall thickness, and casing oil cavity shape parameters, establish a corresponding casing equivalent model for each classification label; Obtain the manufacturer and model of the casing to be measured to determine the corresponding casing equivalent model; based on the corresponding casing equivalent model of the casing to be measured, form an installation interval for the ultrasonic probe from the casing root position to the maximum oil level height position; within the installation interval, based on a sliding window, determine the installation position of the ultrasonic probe.

[0008] Preferably, in the casing equivalent model, taking the center point position of the casing root as the coordinate origin, a three-dimensional coordinate system is established based on the coordinate origin, and the coordinates of the center point of the casing root are , and the coordinates of the maximum oil level height are , where is the maximum oil level height, and are the values in the established three-dimensional coordinate system, and , , , are the radii of the casing cross-section in the axis direction and in the axis direction respectively; The sliding window longitudinally moves upward from the root position of the bushing within the installation interval; during the longitudinal movement, marks are made while simultaneously satisfying the change rate of the bushing porcelain wall thickness within a sliding window with a length of is not greater than 1%, and the attenuation rate of the ultrasonic signal within a sliding window with a length of is not greater than 1‰, and the positions of the sliding windows are marked; For each marked sliding window position, it makes a transverse movement along the outer wall of the bushing equivalent model, and during the transverse movement, the maximum distance value between each marked sliding window position and the live part of the transformer is marked; when the maximum distance value corresponding to the sliding window position is greater than the designed safety value, the sliding window position is used as the quasi-installation position of the ultrasonic probe. Taking the quasi-installation position of the ultrasonic probe as the center of the sliding window, while simultaneously satisfying the change rate of the bushing porcelain wall thickness within a sliding window with a length of is not greater than 1%, and the attenuation rate of the ultrasonic signal within a sliding window with a length of is not greater than 1‰, the quasi-installation position is used as the installation position of the ultrasonic probe. Preferably, based on the installation position of the ultrasonic probe and the bushing equivalent model corresponding to the bushing to be measured, a simulation method is adopted. According to the dielectric constant of the insulating oil inside the bushing to be measured and the porcelain wall thickness, 15 MHz is used as the initial value of the emission frequency of the emission module at the ultrasonic probe. With the goal that the ultrasonic wave emitted by the ultrasonic probe can penetrate the bushing wall thickness and the ultrasonic probe can receive the echo signal, the emission frequency of the emission module at the ultrasonic probe is adjusted and the emission power is adjusted through the power module. Preferably, the upper computer adopts a simulation method to extract the effective echo signal from the echo signal according to the installation position of the ultrasonic probe, the emission power and the emission frequency of the ultrasonic probe, including:

[0009] Using the ambient temperature to correct the acoustic impedance of air, the acoustic impedance of the bushing wall surface at the installation position of the ultrasonic probe, and the acoustic impedance of the insulating oil;

[0010] Using the corrected acoustic impedance of air and the acoustic impedance of the bushing wall surface, calculate the sound pressure reflection coefficient of the echo when there is no oil in the bushing; use the sound pressure reflection coefficient of the echo when there is no oil in the bushing to calculate the sound intensity reflectivity of each echo; use the corrected acoustic impedance of air and the acoustic impedance of the insulating oil to calculate the sound pressure reflection coefficient of the echo when there is oil in the bushing; use the sound pressure reflection coefficient of the echo when there is oil in the bushing to calculate the sound intensity reflectivity of each echo; Using the sound intensity reflectivities of each echo when there is no oil in the bushing and when there is oil in the bushing, calculate the sensitivity difference of each echo; when the sensitivity difference of the When the sensitivity difference of the th echo is greater than the set threshold, take the ... th echo... The next echo is used as the effective echo signal; The host computer uses a simulation method to determine the propagation duration of the effective echo signal when there is no oil in the casing based on the casing equivalent model corresponding to the casing to be measured and the propagation duration of the effective echo signal when there is no oil in the casing , and the propagation duration is the difference between the reception time of the effective echo signal and the transmission time of the ultrasonic signal.

[0011] Preferably, the acoustic impedance of air and the ambient temperature satisfy the following relational expression:

[0012] In the formula, is the acoustic impedance of air, is the ambient air pressure, is the specific heat ratio, is the molar mass, is the gas constant, is the ambient temperature; The acoustic impedance of insulating oil and the ambient temperature satisfy the following relational expression:

[0013] In the formula, is the acoustic impedance of insulating oil, is the density of insulating oil at 20°C, is the coefficient of volume expansion; The acoustic impedance of the casing wall and the ambient temperature satisfy the following relational expression:

[0014] In the formula, is the acoustic impedance of the casing wall, is the elastic modulus, which decreases as the ambient temperature increases, is the coefficient of linear expansion, is the change in ambient temperature.

[0015] Preferably, the sound pressure reflection coefficient of the echo when there is no oil in the casing and the sound intensity reflectivity of each echo respectively satisfy the following relational expressions:

[0016] , , ……,

[0017] In the formula, is the sound pressure reflection coefficient of the echo when there is no oil in the casing, , , ……, They are the sound intensity reflectivity of the first echo, the second echo, ……, the th echo when there is no oil in the casing; The sound pressure reflection coefficient of the echo when there is oil in the casing and the sound intensity reflectivity of each echo respectively satisfy the following relational expressions:

[0018] , , ……,

[0019] wherein, is the sound pressure reflection coefficient of the echo when there is no oil in the casing, , , ……, are respectively the sound intensity reflectivity of the first echo, the second echo, ……, the th echo when there is oil in the casing; The sensitivity difference of each echo satisfies the following relational expression:

[0020] wherein, is the sensitivity difference of the th echo, , are respectively the sound intensity reflectivity of the th echo when there is no oil in the casing and when there is oil in the casing, .

[0021] Preferably, the set threshold is 8 dB.

[0022] Preferably, the position sensor in the detection device transmits the current position of the ultrasonic probe to the upper computer, and the upper computer verifies the deviation between the current position of the ultrasonic probe and the determined installation position. When the deviation is not less than the set single - movement distance, the upper computer sends a movement instruction to the lifting platform in the detection device; when the deviation is less than the set single - movement distance, the upper computer sends a detection instruction to the detection device; wherein, the movement instruction includes: an instruction to rise by a single - movement distance and an instruction to descend by a single - movement distance; When the detection device receives the detection instruction, it detects the propagation duration of the effective echo signal in the casing to be measured and uploads it to the upper computer; the upper computer uses the propagation duration of the effective echo signal when there is no oil in the casing, the propagation duration of the effective echo signal when there is oil in the casing, and the propagation duration of the effective echo signal in the casing to be measured to judge whether the oil level is detected; When it is determined that the oil level is not detected, the host computer sends an instruction of the single - descent moving distance to the lifting platform in the detection device, and repeatedly detects the propagation duration of the effective echo signal in the sleeve to be measured and determines whether the oil level is detected; When it is determined that the ultrasonic probe detects the oil level, the position sensor sends the current position signal of the ultrasonic probe to the host computer, and the host computer outputs the sleeve oil level.

[0023] Preferably, the ultrasonic probe includes: an upper ultrasonic probe and a lower ultrasonic probe; and the upper ultrasonic probe is arranged above the lower ultrasonic probe; Taking the center point position of the sleeve root as the coordinate origin, the position sensor obtains the first distance between the position of the upper ultrasonic probe and the coordinate origin, and the second distance between the position of the lower ultrasonic probe and the coordinate origin, and takes the distance between the average value of the first distance and the second distance and the coordinate origin as the current position signal of the ultrasonic probe and transmits it to the analog port of the controller; the controller uploads the current position signal of the ultrasonic probe to the host computer, and the host computer determines whether there is a deviation between the current position of the ultrasonic probe and the determined installation position. When the deviation is not less than the set single - moving distance, the host computer sends a moving instruction to the lifting platform in the detection device, where the single - moving distance is 1 cm.

[0024] Preferably, when the host computer determines that the oil level is detected, otherwise it determines that the oil level is not detected; The upper ultrasonic probe and the lower ultrasonic probe respectively detect the propagation duration of the effective echo signal in the sleeve to be measured and determine whether the oil level is detected according to the above - mentioned relational expression, including: when it is determined that neither the upper ultrasonic probe nor the lower ultrasonic probe detects the oil level, it is determined that the oil level is not detected; when it is determined that the upper ultrasonic probe does not detect the oil level and the lower ultrasonic probe detects the oil level, it is determined that the oil level is detected; when it is determined that both the upper ultrasonic probe and the lower ultrasonic probe detect the oil level, it is determined that the oil level is detected; When it is determined that the oil level is detected, the sleeve oil level is the distance between the average value of the first distance and the second distance and the coordinate origin.

[0025] Preferably, when the sleeve oil level is lower than the rated oil level of the sleeve but higher than the abnormal oil level of the sleeve, the host computer uses the two detected sleeve oil levels and the corresponding detection times to determine the oil - level drop rate. If the oil - level drop rate increases, an oil - level alarm is issued.

[0026] The present invention also proposes a detection system for the oil level of an oil - immersed transformer sleeve, including: a host computer and a detection device; Among them, the host computer includes: a detection - device initialization module, an effective - echo determination module, an installation - position verification module, and a sleeve - oil - level detection module; The detection device initialization module is used to collect the parameters of the casing to be measured, and determine the installation position of the ultrasonic probe in the detection device by using a simulation method; according to the installation position of the ultrasonic probe, with the goal that the ultrasonic wave emitted by the ultrasonic probe can penetrate the casing wall thickness and the ultrasonic probe can receive the echo signal, determine the transmission power and transmission frequency of the ultrasonic probe; The effective echo determination module is used to determine, by using a simulation method according to the installation position of the ultrasonic probe, the transmission power and transmission frequency of the ultrasonic probe, from the secondary echo signals, determine the th echo that meets the detection sensitivity requirements as the effective echo signal, and determine the propagation duration of the effective echo signal when there is no oil in the casing and the propagation duration of the effective echo signal when there is oil in the casing; The installation position verification module is used to, according to the installation position of the ultrasonic probe, after fixing the detection device on the side wall of the casing, verify whether there is a deviation between the current position of the ultrasonic probe and the installation position; if there is no deviation, send a detection instruction to the detection device; When the detection device receives the detection instruction, it detects the propagation duration of the effective echo signal in the casing to be measured and uploads it to the host computer; The casing oil level detection module is used to use the propagation duration of the effective echo signal when there is no oil in the casing, the propagation duration of the effective echo signal when there is oil in the casing, and the propagation duration of the effective echo signal in the casing to be measured to determine whether the ultrasonic probe detects the oil level; when it is determined that the ultrasonic probe detects the oil level, the host computer outputs the casing oil level.

[0027] The present invention is also a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method.

[0028] The present invention is also a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, the steps of the method are implemented.

[0029] The beneficial effect of the present invention is that, compared with the prior art, the ultrasonic probe is installed on a lifting platform to realize real-time adjustment of the detection position. According to the energy loss difference of ultrasonic waves in insulating oil and air, an energy attenuation algorithm is used to calculate the oil level situation in the casing, and according to the oil level measurement result of the probe, the moving direction of the lifting platform is controlled. The detection device combines multiple criteria such as the oil level drop rate, the rated oil level, and the abnormal oil level level to complete real-time monitoring of the casing oil level, greatly improving the real-time performance and accuracy of casing oil level monitoring, and finally completing precise monitoring of the specific value of the oil level. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is an installation schematic diagram of the detection device for the oil level of the oil-immersed transformer casing proposed by the present invention; Figure 2 It is the layout diagram of the lifting platform in the detection device for the oil level of the oil-immersed transformer bushing proposed by the present invention; Figure 2 The description of the reference numerals in the figure is as follows: 1 - 24V stepper motor, 2 - vertical lifting guide rail, 3 - position sensor, 4 - ultrasonic probe mounting surface, 5 - signal wire groove, 6 - fixing bracket; Figure 3 It is the working principle diagram of the lifting platform in the embodiment of the present invention. Specific embodiments

[0031] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the spirit of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0032] The present invention proposes a method for detecting the oil level of an oil-immersed transformer bushing, including: Step 1, the upper computer collects the parameters of the oil-immersed transformer bushing, and determines the installation position of the ultrasonic probe in the detection device by using a simulation method; according to the installation position of the ultrasonic probe, the upper computer determines the transmission power and transmission frequency of the ultrasonic probe with the goal that the ultrasonic wave emitted by the ultrasonic probe can penetrate the wall thickness of the bushing and the ultrasonic probe can receive the echo signal. [[ID=1,8]]

[0033] Specifically, Step 1 includes: Step 1.1, the upper computer collects the parameters of the oil-immersed transformer bushings in each substation, including the manufacturer, model, maximum oil level height, internal insulating oil dielectric constant, bushing porcelain wall thickness, and bushing oil cavity shape parameters; using the manufacturer and model as classification labels, and using the maximum oil level height, internal insulating oil dielectric constant, bushing porcelain wall thickness, and bushing oil cavity shape parameters, establish an equivalent model of the bushing corresponding to each classification label. ]>

[0034] Specifically, in the bushing equivalent model, taking the center point position of the bushing root as the coordinate origin, a three-dimensional coordinate system is established based on the coordinate origin, and the coordinates of the center point of the bushing root are and the coordinates of the maximum oil level height are where, is the maximum oil level height, and are the values in the established three-dimensional coordinate system, and [[ID=]

[35] ] are respectively the cross-section of the bushing in the axis direction and in the ​​​Radius in the axial direction.

[0035] Step 1.2: Obtain the manufacturer and model of the casing to be measured to determine the corresponding casing equivalent model; based on the casing equivalent model corresponding to the casing to be measured, form the installation interval of the ultrasonic probe from the position of the casing root to the position of the maximum oil level height; within the installation interval, determine the installation position of the ultrasonic probe based on the sliding window.

[0036] Specifically, the installation position of the ultrasonic probe includes: Step : The sliding window moves longitudinally upward from the position of the casing root within the installation interval; during the longitudinal movement, mark the positions of the sliding windows that simultaneously satisfy that the change rate of the casing porcelain wall thickness within the sliding window with a length of is not greater than 1%, and the attenuation rate of the ultrasonic signal within the sliding window with a length of is not greater than 1‰. Step : For each marked sliding window position, move it horizontally along the outer wall of the casing equivalent model, and mark the maximum distance value between each sliding window position and the live part of the transformer during the horizontal movement; when the maximum distance value corresponding to the sliding window position is greater than the designed safety value, use the sliding window position as the quasi-installation position of the ultrasonic probe; in the embodiment, the designed safety value is the safety clearance under each voltage level specified in the electric power standard specification. Step : With the quasi-installation position of the ultrasonic probe as the center of the sliding window, the quasi-installation position that simultaneously satisfies that the change rate of the casing porcelain wall thickness within the sliding window with a length of is not greater than 1%, and the attenuation rate of the ultrasonic signal within the sliding window with a length of is not greater than 1‰ is used as the installation position of the ultrasonic probe. In the present invention, for the casing to be measured, the corresponding casing parameters in the casing model library are selected. According to the maximum oil level height value and the porcelain wall thickness distribution in the casing parameters, several casing wall surfaces with uniform thickness and small ultrasonic signal attenuation rate within the oil level detection range are selected as the candidate positions, and a circle is surrounded along the outer wall through the candidate positions to ensure the maximum safety distance from the live equipment of the transformer; due to the reasons of casing production and manufacturing, it is also necessary to check whether the porcelain wall thickness distribution is uniform and whether the ultrasonic signal attenuation rate is small after surrounding a circle along the outer wall through the candidate positions. Only after the check is satisfied can the safe position of the ultrasonic probe be determined. However, determining the safe position of the ultrasonic probe is carried out based on the casing equivalent model corresponding to the casing to be measured. To ensure the accuracy of the measurement, it is also necessary to correct according to the measurement data of the actual casing based on the determined installation position of the ultrasonic probe.

[0037] Step 1.3: Based on the installation position of the ultrasonic probe, with the aim that ultrasonic waves can penetrate the wall thickness of the casing and receive echo signals, determine the transmission power and transmission frequency of the ultrasonic probe.

[0038] In the embodiment, based on the installation position of the ultrasonic probe, using a simulation method based on the equivalent model of the casing corresponding to the casing to be measured, according to the relative permittivity of the insulating oil inside the casing to be measured and the wall thickness of the porcelain wall, adjust the transmission frequency of the transmission module at the ultrasonic probe. Take 15 MHz as the initial value of the transmission frequency, and appropriately adjust the probe transmission power through the power supply module to ensure that ultrasonic waves can penetrate the casing wall surface and its echo signal can be accurately collected by the ultrasonic receiving module.

[0039] In the intelligent monitoring of the oil level in the oil-immersed transformer casing, the selection and determination of the installation position of the ultrasonic probe have a certain impact on the detection result. In the prior art, the ultrasonic probe is often installed according to the operation experience of personnel; the present invention selects and determines the installation position based on the equivalent model of the casing, and also selects and determines the transmission power and transmission frequency of the ultrasonic probe, realizing the positioning operation before on-site detection and the setting operation of the transmission parameters.

[0040] Step 2: The upper computer uses a simulation method according to the installation position of the ultrasonic probe, the transmission power and transmission frequency of the ultrasonic probe, and determines the th echo signal that meets the detection sensitivity requirement from the th echo as the effective echo signal, and determines the propagation duration of the effective echo signal when there is no oil in the casing and the propagation duration of the effective echo signal when there is oil in the casing.

[0041] The installation position and emission parameters determined in Step 1 are both obtained based on simulation means, which solve the layout and positioning problem that the ultrasonic probe emission signal can meet the detection requirements under the ideal state of uniform casing wall thickness and internal insulating oil. However, the casing to be measured has usually been in operation for some time. Therefore, an ultrasonic detection device is used to conduct a detection effect test on the oil level of the casing to be measured. The ultrasonic probe converts the electrical signal into a pressure signal, which propagates in the air in the form of waves. When the ultrasonic wave is vertically incident on the liquid surface, most of the waves with energy will be reflected (a small part will enter the insulating oil inside the casing) and received by the ultrasonic probe again. When the acoustic wave frequency is constant, the attenuation of the acoustic wave amplitude is related to factors such as the density and elasticity of the medium. By measuring the change in the energy attenuation of the ultrasonic wave in the medium, the change in the oil level inside the casing can be identified. Thus, the distance from the liquid surface to the measurement point can be calculated using the fixed propagation speed of the ultrasonic wave and the measured time value, completing the oil level detection based on the ultrasonic oil level detection algorithm. Therefore, based on the determined installation position and emission parameters, the number of echoes with a reflection signal difference meeting the detection requirements is further determined through simulation means, and the echoes with the determined number are used as effective echo signals for oil level detection.

[0042] Specifically, Step 2 includes: Step 2.1, using the ambient temperature to correct the acoustic impedance of air, the acoustic impedance of the casing wall surface at the ultrasonic probe installation position, and the acoustic impedance of the insulating oil; Since the reflection effect of the ultrasonic wave on the inner wall of the corresponding casing is greatly affected by environmental factors, the influence of the measurement ambient temperature in the echo calculation is mainly considered in the algorithm of the present invention to correct the calculation results of the acoustic impedance of air, the acoustic impedance of the casing wall surface, and the acoustic impedance of the insulating oil; The acoustic impedance of air and the ambient temperature satisfy the following relationship:

[0043] In the formula, is the acoustic impedance of air, is the ambient air pressure, is the specific heat ratio, is the molar mass, is the gas constant, is the ambient temperature; When the ambient air pressure is constant, an increase in the ambient temperature will cause a decrease in the acoustic impedance of air.

[0044] The acoustic impedance of the insulating oil and the ambient temperature satisfy the following relationship:

[0045] In the formula, is the acoustic impedance of the insulating oil, is the density of the insulating oil at 20°C, Coefficient of volume expansion; The acoustic impedance of the insulating oil increases with the increase of the ambient temperature, but decreases after reaching the extreme value.

[0046] The acoustic impedance of the solid on the bushing wall is affected by thermal expansion and the change of elastic modulus. The acoustic impedance of the bushing wall and the ambient temperature satisfy the following relationship:

[0047] In the formula, is the acoustic impedance of the bushing wall, is the elastic modulus, which decreases with the increase of the ambient temperature, is the linear expansion coefficient, is the change amount of the ambient temperature; The acoustic impedance of the wall decreases with the increase of the ambient temperature.

[0048] In the embodiment, taking the bushing of a certain oil-immersed transformer as an example, it is calculated that at room temperature of 20 °C, the acoustic impedance of air is 0.0004 , the acoustic impedance of the insulating oil is 0.128 , and the acoustic impedance of the bushing wall is 46.0 ; Step 2.2, using the corrected acoustic impedance of air and the acoustic impedance of the bushing wall, calculate that the acoustic pressure reflection coefficient of the echo when there is no oil in the bushing satisfies the following relationship:

[0049] In the formula, is the acoustic pressure reflection coefficient of the echo when there is no oil in the bushing; Calculate the acoustic intensity reflectivity of each echo by using the acoustic pressure reflection coefficient of the echo when there is no oil in the bushing, and it satisfies the following relationship: , , ……,

[0050] In the formula, , , ……, are the acoustic intensity reflectivities of the first echo, the second echo, ……, the th echo when there is no oil in the bushing respectively; Using the corrected acoustic impedance of air and the acoustic impedance of the insulating oil, calculate that the acoustic pressure reflection coefficient of the echo when there is oil in the bushing satisfies the following relationship:

[0051] In the formula, is the sound pressure reflection coefficient of the echo when there is no oil in the casing; Calculate the sound intensity reflectivity of each echo by using the sound pressure reflection coefficient of the echo when there is oil in the casing, and the following relationship is satisfied: , , ……,

[0052] In the formula, 、 、……、 are the sound intensity reflectivities of the first echo, the second echo, ……, the -th echo when there is oil in the casing respectively; In the embodiment, the ultrasonic echoes under two conditions of no oil in the casing and oil at the measurement point are respectively detected in the laboratory environment, and the sound pressure reflection coefficient in the echo is calculated and the sound intensity reflectivity . When there is no oil at the measurement point, the ultrasonic wave passes through the wall and is reflected by the internal cable layer after being absorbed by the air. At this time, the sound pressure reflection coefficient of the echo , the first energy attenuation occurs at the first echo. At this time, the sound intensity reflectivity . At the second echo, the energy decays for the second time. Because the acoustic impedance difference between the casing wall and the air under normal temperature and pressure is too large, the transmission situation at the interface between the casing wall and the air can be ignored, that is, the ultrasonic wave is fully reflected at the interface between the casing wall and the air. Therefore, the sound intensity reflectivity of the second echo . By analogy, the sound intensity reflectivity at the n-th echo when there is no oil inside the casing can be calculated.

[0053] Similarly, when there is insulating oil in the casing, the ultrasonic wave passes through the wall and is reflected by the internal cable layer after being absorbed by the insulating oil. At this time, the sound pressure reflection coefficient of the echo , the first energy attenuation starts after the first echo. At this time, the sound intensity reflectivity . At the second echo, the energy decays for the second time, and the sound intensity reflectivity . By analogy, the sound intensity reflectivity at the n-th echo can be calculated.

[0054] Step 2.3, calculate the sensitivity difference of each echo by using the sound intensity reflectivities of each echo when there is no oil in the casing and when there is oil in the casing, and the following relationship is satisfied:

[0055] In the formula, is the sensitivity difference of the -th echo, 、 are the sound intensity reflectivities of the -th echo when there is no oil in the casing and when there is oil in the casing respectively, ; When the sensitivity difference of the th echo is greater than the set threshold, the th echo is used as the effective echo signal; In the embodiment, the sensitivity difference of the th echo is such that when > 8dB, it is determined that the reflection signal difference of the th echo is already very large and can be used as an effective echo signal to participate in the oil level detection; Step 2.4, the host computer uses a simulation method to determine the propagation duration of the effective echo signal when there is no oil in the casing and the propagation duration of the effective echo signal when there is oil in the casing based on the equivalent casing model corresponding to the casing to be measured. The propagation duration is the difference between the reception time of the effective echo signal and the transmission time of the ultrasonic signal.

[0056] The present invention uses an ultrasonic detection technology based on an energy attenuation algorithm, mainly utilizing the propagation and echo characteristics of ultrasonic waves. At a fixed frequency, the echoes of ultrasonic pulses are collected, and by calculating the echo velocity of the sound wave passing through different media, the oil level height of the measured casing is converted therefrom. It is quite different from the existing infrared image detection technology. In terms of measurement accuracy, the present invention can control the measurement range to the millimeter level through the acoustic loss algorithm, while the infrared image detection technology mainly makes judgments from the visual aspect and cannot quantify the oil level in the casing; in terms of anti-interference, when the present invention is used, the liquid level is mainly judged through ultrasonic signals and is less affected by the strong electromagnetic field around the casing, having the technical characteristics of safe measurement method, high accuracy, and strong reliability. Other liquid level detection technologies including the infrared image detection technology are easily affected by interference sources such as the electromagnetic field, sunlight, and background noise around the casing.

[0057] Step 3, according to the installation position of the ultrasonic probe, fix the detection device on the side wall of the casing; the host computer checks whether there is a deviation between the current position and the installation position of the ultrasonic probe; if there is no deviation, the host computer sends a detection instruction to the detection device; when the detection device receives the detection instruction, it measures the propagation duration of the effective echo signal in the casing to be measured and uploads it to the host computer; the host computer uses the propagation duration of the effective echo signal when there is no oil in the casing, the propagation duration of the effective echo signal when there is oil in the casing, and the propagation duration of the effective echo signal in the casing to be measured to determine whether the ultrasonic probe detects the oil level; when it is determined that the ultrasonic probe detects the oil level, the host computer outputs the oil level of the casing.

[0058] Specifically, Step 3 includes: Step 3.1: The position sensor in the detection device transmits the current position of the ultrasonic probe to the host computer. The host computer verifies the deviation between the current position of the ultrasonic probe and the determined installation position. When the deviation is not less than the set single - movement distance, the host computer sends a movement instruction to the lifting platform in the detection device; when the deviation is less than the set single - movement distance, the host computer sends a detection instruction to the detection device. Among them, the movement instruction includes: an instruction to rise by the single - movement distance and an instruction to descend by the single - movement distance. As Figure 1 shown, the detection device for the oil level of the oil - immersed transformer bushing proposed by the present invention is arranged on the side wall of the oil - immersed transformer bushing. The detection device includes: an ultrasonic upper - end probe 10, an ultrasonic lower - end probe 20, a lifting platform 30, a host computer 40, and an RS485 transmission wire harness 50. As Figure 2 shown, the lifting platform includes a controller, a 24V stepper motor 1, a vertical lifting guide rail 2, a position sensor 3, an ultrasonic - probe mounting surface 4, a signal wire groove 5, and a fixing frame 6. Among them, the ultrasonic upper - end probe and the ultrasonic lower - end probe are fixed on the ultrasonic - probe mounting surface, and the ultrasonic upper - end probe is arranged above the ultrasonic lower - end probe. As Figure 3 shown, to accurately position the ultrasonic probe, taking the center - point position of the bushing root as the coordinate origin, the position sensor obtains the first distance between the position of the ultrasonic upper - end probe and the coordinate origin and the second distance between the position of the ultrasonic lower - end probe and the coordinate origin, and takes the distance between the average value of the first distance and the second distance and the coordinate origin as the current - position signal of the ultrasonic probe and transmits it to the analog - quantity port of the controller. The controller uploads the current - position signal of the ultrasonic probe to the host computer. The host computer determines whether there is a deviation between the current position of the ultrasonic probe and the installation position determined in Step 1. When the deviation is not less than the set single - movement distance, the host computer sends a movement instruction to the lifting platform in the detection device. In the embodiment, the single - movement distance is 1 cm. When the controller receives the movement instruction sent by the host computer, it sends a conduction signal to the contact switch through the digital - quantity port of the controller. The contact switch is directly powered by the power - supply module, and then the digital - quantity port of the controller sends a control pulse to the 24V stepper motor. The 24V stepper motor drives the slider to drive the two ultrasonic probes to move longitudinally up or down on the vertical lifting guide rail. When the host computer determines that the deviation between the position of the ultrasonic probe after movement and the safe position is less than the set single - movement distance, the internal interrupt program of the host computer sends a voltage signal with an amplitude greater than 0.02V and less than or equal to 5V to the analog - quantity port of the controller. At the same time, the digital - quantity port of the controller stops sending pulses to the 24V stepper motor, the 24V stepper motor stops working, and then the digital - quantity port of the controller sends a break - off signal to the contact switch. When the deviation is less than the set single - movement distance, the host computer sends a detection instruction to the detection device. The position sensor records the position of the ultrasonic probe after movement as the new starting point and waits for the next instruction from the host computer.

[0059] In the embodiment, the controller includes an Arduino Uno controller. The digital port of the Arduino Uno controller sends pulses to a 24V stepper motor through a stepper motor driver TB6600. The power supply module includes a 5V DC switching power supply.

[0060] Step 3.2, when the detection device receives the detection instruction, it detects the propagation duration of the effective echo signal in the sleeve to be measured. And uploads it to the host computer. The host computer uses the propagation duration of the effective echo signal when there is no oil in the sleeve, the propagation duration of the effective echo signal when there is oil in the sleeve, and the propagation duration of the effective echo signal in the sleeve to be measured to determine whether the oil level is detected. Specifically, when the host computer determines that the oil level is detected; otherwise, it determines that the oil level is not detected. Furthermore, the upper ultrasonic probe and the lower ultrasonic probe respectively detect the propagation duration of the effective echo signal in the sleeve to be measured, and determine whether the oil level is detected according to the above - mentioned relational expression, including: when it is determined that neither the upper ultrasonic probe nor the lower ultrasonic probe detects the oil level, it is determined that the oil level is not detected; when it is determined that the upper ultrasonic probe does not detect the oil level and the lower ultrasonic probe detects the oil level, it is determined that the oil level is detected; when it is determined that both the upper ultrasonic probe and the lower ultrasonic probe detect the oil level, it is determined that the oil level is detected. Step 3.3, when it is determined that the oil level is not detected, the host computer sends an instruction to the lifting platform in the detection device to lower the single - movement distance and repeats step 3.2. Step 3.4, when it is determined that the oil level is detected, the position sensor sends the current position signal of the ultrasonic probe to the host computer, and the host computer outputs the oil level of the sleeve. Furthermore, when there are an upper ultrasonic probe and a lower ultrasonic probe, the oil level of the sleeve is the distance from the average value of the first distance and the second distance to the coordinate origin. When the oil level of the sleeve is lower than the rated oil level of the sleeve but higher than the abnormal oil level of the sleeve, the host computer uses the two detected oil levels of the sleeve and the corresponding detection times to determine the oil - level drop rate. If the oil - level drop rate increases, an oil - level alarm is issued.

[0061] Therefore, the present invention, combined with the in-station intelligent auxiliary system, can realize non-contact real-time monitoring of the bushing oil level. By quantifying the transformer bushing oil level, front-line operation and maintenance personnel can also accurately and quickly diagnose the bushing operating status, thereby avoiding operational failures caused by abnormal bushing oil level, enhancing the safety and stability of power system operation, and its high-precision measurement performance also meets the requirements of smart substations, with strong use value and promotion significance.

[0062] The present invention also proposes a detection system for oil level of oil-immersed transformer bushing, comprising: a host computer and a detection device; The host computer includes: a detection device initialization module, a valid echo determination module, an installation position verification module, and a casing oil level detection module; The detection device initialization module is used to collect parameters of the casing to be tested and use simulation methods to determine the installation position of the ultrasonic probe in the detection device. Based on the installation position of the ultrasonic probe, the transmission power and transmission frequency of the ultrasonic probe are determined with the goal that the ultrasonic wave emitted by the ultrasonic probe can penetrate the thickness of the casing wall and the ultrasonic probe can receive the echo signal. The effective echo determination module is used to use simulation method to determine the effective echo according to the installation position, transmission power and transmission frequency of the ultrasonic probe. Determine the first echo signal that meets the detection sensitivity requirement The secondary echo is taken as the effective echo signal, and the propagation time of the effective echo signal when there is no oil in the casing and the propagation time of the effective echo signal when there is oil in the casing are determined; The installation position verification module is used to verify whether there is a deviation between the current position of the ultrasonic probe and the installation position after the detection device is fixed on the side wall of the casing according to the installation position of the ultrasonic probe; if there is no deviation, a detection instruction is sent to the detection device; When the detection device receives the detection instruction, it detects the propagation time of the effective echo signal in the casing to be tested and uploads it to the host computer; The casing oil level detection module is used to determine whether the ultrasonic probe has detected the oil level by using the propagation time of the effective echo signal when there is no oil in the casing, the propagation time of the effective echo signal when there is oil in the casing, and the propagation time of the effective echo signal in the casing to be tested. When it is determined that the ultrasonic probe has detected the oil level, the host computer outputs the casing oil level.

[0063] The present disclosure may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0064] A computer-readable storage medium can be a tangible device that can hold and store instructions for use by an instruction execution device. A computer-readable storage medium may be, for example—but not limited to—an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), a memory stick, a floppy disk, a mechanically encoded device such as a punched card or raised structures in grooves having instructions stored thereon, and any suitable combination of the foregoing. The computer-readable storage medium as used herein is not construed as being a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagated through a waveguide or other transmission medium (e.g., an optical pulse through an optical fiber cable), or an electrical signal transmitted through a wire.

[0065] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to various computing / processing devices, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include a copper transmission cable, an optical fiber transmission, a wireless transmission, a router, a firewall, a switch, a gateway computer, and / or an edge server. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in a computer-readable storage medium in each computing / processing device.

[0066] Computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine - related instructions, microcode, firmware instructions, state - setting data, or source code or object code written in any combination of one or more programming languages, including object - oriented programming languages such as Smalltalk, C++, etc., and conventional procedural programming languages such as the "C" language or similar programming languages. The computer - readable program instructions may be executed entirely on the user's computer, partially on the user's computer, executed as a stand - alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or it may be connected to an external computer (e.g., through the Internet using an Internet service provider). In some embodiments, by using the state information of computer - readable program instructions to customize an electronic circuit, such as a programmable logic circuit, a field - programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit can execute the computer - readable program instructions to implement various aspects of the present disclosure.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or make equivalent replacements. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A method for detecting the oil level of an oil-immersed transformer bushing, characterized in that, Including: The host computer collects the parameters of the sleeve to be measured, and determines the installation position of the ultrasonic probe in the detection device by using a simulation method; according to the installation position of the ultrasonic probe, the host computer takes the ultrasonic wave emitted by the ultrasonic probe to penetrate the wall thickness of the sleeve and the ultrasonic probe can receive the echo signal as the goal, and determines the transmission power and transmission frequency of the ultrasonic probe. The host computer uses a simulation method based on the installation position, transmission power, and transmission frequency of the ultrasonic probe to determine, from the secondary echo signals, the th echo that meets the detection sensitivity requirements as the effective echo signal, and determines the propagation duration of the effective echo signal when there is no oil in the casing and the propagation duration of the effective echo signal when there is oil in the casing; According to the installation position of the ultrasonic probe, fix the detection device on the side wall of the sleeve; the host computer checks whether there is a deviation between the current position and the installation position of the ultrasonic probe; if there is no deviation, the host computer sends a detection instruction to the detection device; when the detection device receives the detection instruction, it measures the propagation duration of the effective echo signal in the sleeve to be measured and uploads it to the host computer; the host computer uses the propagation duration of the effective echo signal when there is no oil in the sleeve, the propagation duration of the effective echo signal when there is oil in the sleeve, and the propagation duration of the effective echo signal in the sleeve to be measured to judge whether the oil level is detected; when it is determined that the oil level is detected, the host computer outputs the oil level of the sleeve.

2. The method for detecting the oil level of an oil-immersed transformer sleeve according to claim 1, wherein The host computer collects the parameters of the oil-immersed transformer sleeve and determines the installation position of the ultrasonic probe in the detection device by using a simulation method, including: The host computer collects the parameters of the oil-immersed transformer sleeves in each substation, including the manufacturer, model, maximum oil level height, internal insulating oil dielectric constant, sleeve porcelain wall thickness, and sleeve oil cavity shape parameters; using the manufacturer and model as classification labels, and using the maximum oil level height, internal insulating oil dielectric constant, sleeve porcelain wall thickness, and sleeve oil cavity shape parameters, establish a sleeve equivalent model corresponding to each classification label. Obtain the manufacturer and model of the sleeve to be measured to determine the sleeve equivalent model corresponding to the sleeve to be measured; based on the sleeve equivalent model corresponding to the sleeve to be measured, form an installation interval for the ultrasonic probe from the root position of the sleeve to the maximum oil level height position; within the installation interval, based on the sliding window, determine the installation position of the ultrasonic probe.

3. The method for detecting the oil level of an oil-immersed transformer sleeve according to claim 2, wherein In the equivalent model of the casing, the center point position of the casing root is taken as the coordinate origin, and a three-dimensional coordinate system is established based on the coordinate origin. The coordinates of the center point of the casing root are , and the coordinate of the maximum oil level height is , where is the maximum oil level height, and are the values in the established three-dimensional coordinate system, and , , , are respectively the radii of the casing cross-section in the axis direction and in the axis direction; The sliding window longitudinally moves upward starting from the root position of the bushing within the installation range; during the longitudinal movement, the marked values simultaneously satisfy the change rate of the porcelain wall thickness of the bushing within a sliding window with a length of not greater than 1%, and the attenuation rate of the ultrasonic signal within a sliding window with a length of not greater than 1‰; the position of the sliding window ​ The marked positions of each sliding window move horizontally along the outer wall of the sleeve equivalent model, and during the horizontal movement, mark the maximum distance value between each sliding window position and the live part of the transformer; when the maximum distance value corresponding to the sliding window position is greater than the designed safety value, use the sliding window position as the quasi-installation position of the ultrasonic probe. Taking the quasi-installation position of the ultrasonic probe as the center of the sliding window, and satisfying the change rate of the casing porcelain wall thickness within the sliding window with a length of not exceeding 1%, and the attenuation rate of the ultrasonic signal within the sliding window with a length of not exceeding 1‰, the quasi-installation position is used as the installation position of the ultrasonic probe. ​ 4. The method for detecting the oil level of an oil-immersed transformer sleeve according to claim 3, wherein According to the installation position of the ultrasonic probe, based on the sleeve equivalent model corresponding to the sleeve to be measured, using a simulation method, according to the internal insulating oil dielectric constant and porcelain wall thickness of the sleeve to be measured, taking 15 MHz as the initial value of the transmission frequency of the transmission module at the ultrasonic probe, and taking the ultrasonic wave emitted by the ultrasonic probe to penetrate the wall thickness of the sleeve and the ultrasonic probe can receive the echo signal as the goal, adjust the transmission frequency of the transmission module at the ultrasonic probe and adjust the transmission power through the power module.

5. The method for detecting the oil level of an oil-immersed transformer sleeve according to claim 1, wherein The host computer extracts the effective echo signal from the echo signal by means of a simulation method according to the installation position, transmission power and transmission frequency of the ultrasonic probe, including: Correcting the acoustic impedance of air, the acoustic impedance of the sleeve wall surface at the installation position of the ultrasonic probe, and the acoustic impedance of the insulating oil by using the ambient temperature; Calculating the sound pressure reflection coefficient of the echo when there is no oil in the sleeve by using the corrected acoustic impedance of air and the acoustic impedance of the sleeve wall surface; calculating the sound intensity reflectivity of each echo by using the sound pressure reflection coefficient of the echo when there is no oil in the sleeve; calculating the sound pressure reflection coefficient of the echo when there is oil in the sleeve by using the corrected acoustic impedance of air and the acoustic impedance of the insulating oil; calculating the sound intensity reflectivity of each echo by using the sound pressure reflection coefficient of the echo when there is oil in the sleeve; Calculate the sensitivity difference of each echo using the sound intensity reflectivity of each echo when there is no oil in the casing and when there is oil in the casing; when the sensitivity difference of the th echo is greater than the set threshold, use the th echo as the effective echo signal; The host computer uses a simulation method to determine the propagation duration of the effective echo signal when there is no oil in the casing based on the casing equivalent model corresponding to the casing to be measured. and the propagation duration of the effective echo signal when there is no oil in the casing , where the propagation duration is the difference between the reception time of the effective echo signal and the transmission time of the ultrasonic signal.

6. The method for detecting the oil level of an oil-immersed transformer bushing according to claim 5, wherein The acoustic impedance of air and the ambient temperature satisfy the following relationship: wherein, is the acoustic impedance of air, is the ambient air pressure, is the specific heat ratio, is the molar mass, is the gas constant, is the ambient temperature; The acoustic impedance of insulating oil and the ambient temperature satisfy the following relationship: In the formula, is the acoustic impedance of the insulating oil, is the density of the insulating oil at 20°C, volume expansion coefficient; The acoustic impedance of the sleeve wall surface and the ambient temperature satisfy the following relationship: In the formula, is the acoustic impedance of the casing wall surface, is the elastic modulus, which decreases with the increase of the ambient temperature, is the linear expansion coefficient, is the change in the ambient temperature.

7. The method for detecting the oil level of an oil-immersed transformer bushing according to claim 6, wherein The sound pressure reflection coefficient of the echo when there is no oil in the sleeve and the sound intensity reflectivity of each echo respectively satisfy the following relationships: ， ，……， Wherein, is the sound pressure reflection coefficient of the echo when there is no oil in the casing, , , ……, are respectively the sound intensity reflectivity of the first echo, the second echo, ……, the th echo when there is no oil in the casing; The sound pressure reflection coefficient of the echo when there is oil in the sleeve and the sound intensity reflectivity of each echo respectively satisfy the following relationships: ， ，……， In the formula, is the sound pressure reflection coefficient of the echo when there is no oil in the casing, , , ……, are respectively the sound intensity reflectivities of the first echo, the second echo, ……, the th echo when there is oil in the casing; The sensitivity difference of each echo satisfies the following relationship: Wherein, is the sensitivity difference of the th echo, , are respectively the sound intensity reflectivities of the th echo when there is no oil in the casing and when there is oil in the casing, .

8. The method for detecting the oil level of an oil-immersed transformer bushing according to claim 7, wherein The set threshold is 8 dB.

9. The method for detecting the oil level of an oil-immersed transformer bushing according to claim 1, wherein The position sensor in the detection device transmits the current position of the ultrasonic probe to the host computer, and the host computer verifies the deviation between the current position of the ultrasonic probe and the determined installation position. When the deviation is not less than the set single movement distance, the host computer sends a movement instruction to the lifting platform in the detection device; When the deviation is less than the set single movement distance, the host computer sends a detection instruction to the detection device; Among them, the movement instruction includes: an instruction to rise by a single movement distance and an instruction to fall by a single movement distance; When the detection device receives a detection instruction, it detects the propagation duration of the effective echo signal in the casing to be measured and uploads it to the host computer; the host computer uses the propagation duration of the effective echo signal when there is no oil in the casing , the propagation duration of the effective echo signal when there is oil in the casing , and the propagation duration of the effective echo signal in the casing to be measured to determine whether the oil level is detected; When it is determined that the oil level is not detected, the host computer sends an instruction to the lifting platform in the detection device to lower by a single movement distance, and repeats detecting the propagation duration of the effective echo signal in the bushing to be measured and determining whether the oil level is detected; When it is determined that the ultrasonic probe detects the oil level, the position sensor sends the current position signal of the ultrasonic probe to the host computer, and the host computer outputs the oil level of the bushing.

10. The method for detecting the oil level of an oil-immersed transformer bushing according to claim 9, wherein The ultrasonic probe includes: an ultrasonic upper probe and an ultrasonic lower probe; and the ultrasonic upper probe is arranged above the ultrasonic lower probe; Taking the center point position of the casing root as the coordinate origin, the position sensor obtains the first distance between the position of the upper ultrasonic probe and the coordinate origin, and the second distance between the position of the lower ultrasonic probe and the coordinate origin, and takes the distance between the average value of the first distance and the second distance and the coordinate origin as the current position signal of the ultrasonic probe and transmits it to the analog port of the controller; the controller uploads the current position signal of the ultrasonic probe to the host computer, and the host computer determines whether there is a deviation between the current position of the ultrasonic probe and the determined installation position. When the deviation is not less than the set single movement distance, the host computer sends a movement instruction to the lifting platform in the detection device, where the single movement distance is 1 cm.

11. The method for detecting the oil level of the oil-immersed transformer casing according to claim 10, characterized in that When is true, the host computer determines that the oil level has been detected; otherwise, it determines that the oil level has not been detected. The upper ultrasonic probe and the lower ultrasonic probe respectively detect the propagation duration of the effective echo signal in the casing to be measured, and judge whether the oil level is detected according to the above relational formula, including: when it is determined that neither the upper ultrasonic probe nor the lower ultrasonic probe detects the oil level, it is determined that the oil level is not detected; when it is determined that the upper ultrasonic probe does not detect the oil level and the lower ultrasonic probe detects the oil level, it is determined that the oil level is detected; when it is determined that both the upper ultrasonic probe and the lower ultrasonic probe detect the oil level, it is determined that the oil level is detected. When it is determined that the oil level is detected, the casing oil level is the distance between the average value of the first distance and the second distance and the coordinate origin.

12. The detection method of the oil level of the oil-immersed transformer bushing according to claim 1, characterized in that, It also includes: When the casing oil level is lower than the rated oil level of the casing but higher than the abnormal oil level of the casing, the host computer uses the two detected casing oil levels and the corresponding detection times to determine the oil level drop rate. If the oil level drop rate becomes larger, an oil level alarm is issued.

13. An oil level detection system for an oil-immersed transformer bushing, which is used to implement the oil level detection method for the oil-immersed transformer bushing according to any one of claims 1 to 12, characterized in that, It includes: A host computer and a detection device; Among them, the host computer includes: a detection device initialization module, an effective echo determination module, an installation position verification module, and a casing oil level detection module; The detection device initialization module is used to collect the parameters of the casing to be measured, and use the simulation method to determine the installation position of the ultrasonic probe in the detection device; according to the installation position of the ultrasonic probe, with the goal that the ultrasonic wave emitted by the ultrasonic probe can penetrate the casing wall thickness and the ultrasonic probe can receive the echo signal, determine the transmission power and transmission frequency of the ultrasonic probe. An effective echo determination module, which is used to determine, by means of a simulation method, the nd echo signal that meets the detection sensitivity requirements from the th echo as the effective echo signal, and determine the propagation duration of the effective echo signal when there is no oil in the casing and the propagation duration of the effective echo signal when there is oil in the casing; The installation position verification module is used to verify whether there is a deviation between the current position of the ultrasonic probe and the installation position after the detection device is fixed on the side wall of the casing according to the installation position of the ultrasonic probe; if there is no deviation, a detection instruction is sent to the detection device. When the detection device receives the detection instruction, it detects the propagation duration of the effective echo signal in the casing to be measured and uploads it to the host computer. The casing oil level detection module is used to judge whether the oil level is detected by using the propagation duration of the effective echo signal when there is no oil in the casing, the propagation duration of the effective echo signal when there is oil in the casing, and the propagation duration of the effective echo signal in the casing to be measured; when it is determined that the oil level is reached, the host computer outputs the casing oil level.

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