Transformer oil conservator oil level online monitoring method and system based on ultrasonic technology

Abstract

The invention discloses a transformer oil conservator oil level online monitoring method and system based on an ultrasonic technology, and belongs to the field of power equipment monitoring. The oil level of the transformer is related to equipment safety, a traditional monitoring means has defects, and false oil level is prone to misleading operation and maintenance. With the ultrasonic technology as the core, the multi-band ultrasonic sensor transmits and receives ultrasonic waves to the oil conservator, obtains oil level signals and collects oil temperature and load data at the same time. The oil level is calculated by means of ultrasonic propagation time and a multi-band weighted average algorithm, and the false oil level is discriminated according to oil temperature compensation and load correlation. Through signal conditioning and acquisition, microprocessor operation and wireless communication transmission, data is stored and analyzed in a background monitoring system. The innovative system architecture and algorithm realize high-precision oil level measurement, strong interference resistance, intelligent false oil level discrimination and real-time remote monitoring. On-site tests show that the system stably and accurately monitors complex working conditions, effectively prevents oil level abnormal faults, improves the operation and maintenance efficiency of the transformer and the power supply reliability of a power grid, and firmly guarantees the reliable operation of a power system.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment monitoring, and in particular to an ultrasonic technology-based transformer oil storage cabinet oil level online monitoring method and system. Background Art

[0002] As a key equipment in the power system, the stable operation of the transformer is of vital importance. Transformer oil has both cooling and insulation functions in the transformer, and the oil level is a key parameter reflecting the operating status of the transformer. Abnormal oil level may cause a series of serious problems. For example, when the oil level is too high, according to Pascal's law, the internal pressure of the transformer increases, which damages the life of the equipment; when the oil level is too low, the load capacity of the transformer will be weakened, causing the lead wire or core to be exposed to the air, causing internal flashover, and the contact area between the oil and the air will increase, and the insulation performance will drop sharply.

[0003] There are many defects in the current transformer oil level monitoring methods. Traditional oil level gauges, such as pressure oil level gauges, work on the principle of thermal expansion and contraction, but capillary tubes are prone to problems, resulting in inaccurate temperature and oil level indications. Although the oil temperature and oil level gauge is simple and intuitive, it is difficult to detect sudden changes in oil temperature, the monitoring data is not accurate, and it relies on manual observation, which is labor-intensive and not suitable for large transformers. The infrared temperature imaging method determines the oil level by collecting images and temperature differences. Although it has high accuracy, the image processing is complex, and it requires strict professional quality of personnel. It is also affected by ambient temperature, meteorological conditions and observation angle, resulting in large deviations in measurement results. In addition, traditional oil level gauges are easily affected by factors such as meter jamming, float oil leakage, capsule wrinkling or damage, etc., causing the phenomenon of "false oil level", which causes inspection personnel to misjudge, interferes with operation and maintenance decisions, and seriously threatens the safety of transformers and power grids. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention aims to provide a transformer oil storage cabinet oil level online monitoring method and system based on ultrasonic technology, which can accurately and real-time monitor the oil level, effectively identify "false oil level", improve the transformer operation safety and reliability, and reduce operation and maintenance costs and manpower investment.

[0005] The present invention adopts the following technical solution:

[0006] A first aspect of the present invention provides an online monitoring method for oil level in a transformer oil storage cabinet based on ultrasonic technology, comprising the following steps:

[0007] Step 1: Use a multi-band ultrasonic sensor to transmit ultrasonic waves into the oil storage tank and receive echo signals reflected from the oil surface;

[0008] Step 2, synchronously collect transformer oil temperature and load data;

[0009] Step 3, calculating the oil level height based on ultrasonic propagation time and multi-band weighted average algorithm;

[0010] Step 4, correct the oil level calculation result in combination with the transformer load data: according to the pre-established load-oil level correlation model, when the load changes, predict the corresponding change trend of the oil level, predict the oil level according to the load-oil level correlation model, and perform weighted average of the predicted value and the calculated oil level height to obtain a more accurate oil level estimate;

[0011] Step 5: Establish an oil temperature-oil level change model and combine it with a load-oil level correlation model to determine in real time whether the oil level change conforms to normal physical laws, including that when the oil temperature rises, the oil level should rise accordingly according to the principle of thermal expansion and contraction; when the load increases, the oil temperature rise may cause the oil level to rise. If the oil level change does not conform to the expected law, it is determined that there may be a false oil level.

[0012] Step 6: Provide decision suggestions based on the type and severity of the false oil level.

[0013] Step 7: Remotely transmit the oil level data and related status information and decision recommendations to the background monitoring system.

[0014] Further, step 3 specifically includes: including:

[0015] The ultrasonic propagation time after multi-band weighted averaging measures the oil level height H as shown in the following formula:

[0016]

[0017] H=H 总 -S 综合

[0018] S i =V×t / 2

[0019] In the formula, assume different frequencies f i Corresponding sensor to oil level distance S i , weight ω i , V is the ultrasonic wave propagation speed, transit time t = t 1 -t 0 ,t 1 is the time of receiving the echo, t 0 is the launch time, H 总 is the total height of the oil storage tank.

[0020] Furthermore, the oil temperature-oil level variation model calculates the oil temperature and load to determine the influence of temperature on the oil level H. 温 As shown in the following formula:

[0021] H 温 =H 0 ×(1+α×ΔT)

[0022] In the formula, temperature compensation, assuming oil thermal expansion coefficient α, temperature change ΔT, initial test oil level H 0 :

[0023] The load-oil level correlation model establishes the relationship between load L and oil level change f(L) based on data statistics, and calculates the load impact on oil level H 负 :

[0024] H 负 =f(L).

[0025] Introducing comprehensive feature P 综合 The ultrasonic propagation time after multi-band weighted average is corrected to measure the oil level height H, where g i is the fusion coefficient, P i The characteristics at different frequencies are the amplitude, phase or arrival time of the echo signal, and the corrected S 综合 for

[0026] Furthermore, the multi-band ultrasonic sensor is installed on the side or top of the oil storage tank to ensure that the ultrasonic wave is incident vertically on the oil surface and avoids areas with strong electromagnetic interference.

[0027] Furthermore, the multi-band ultrasonic sensor transmits ultrasonic pulses into the oil storage tank according to a preset frequency sequence and time interval.

[0028] Furthermore, the echo signal is amplified and filtered and converted into a digital signal. The transit time Δt is calculated based on the time stamps of the transmitted and received echoes. The ultrasonic propagation velocity table at different temperatures pre-stored in the microprocessor is used, combined with the oil temperature data collected in real time by the temperature sensor, to calculate the ultrasonic propagation velocity V at the current temperature.

[0029] Furthermore, the judgment logic for determining the possible existence of a false oil level is:

[0030] Set the oil temperature change rate threshold ΔT th and oil level change rate threshold ΔH th , when the oil temperature change rate exceeds ΔT th And the oil level change rate does not reach ΔH th When the load change rate exceeds the set threshold value and the oil level changes abnormally, it is determined to be a suspected false oil level. The historical data is compared and the oil level change trend is analyzed to confirm whether it is a false oil level.

[0031] When a false oil level is detected, a warning signal is issued, which is sent to the background monitoring system and triggers the sound and light alarm locally to alert the on-site operation and maintenance personnel.

[0032] Another aspect of the present invention provides an online monitoring system for oil level in a transformer oil storage cabinet based on ultrasonic technology.

[0033] It includes: a sensor module, including a multi-band ultrasonic sensor, a temperature sensor and a load sensor, which uses the multi-band ultrasonic sensor to transmit ultrasonic waves into the oil storage cabinet and receive echo signals reflected by the oil surface, and the temperature sensor and the load sensor respectively synchronously collect transformer oil temperature and load data;

[0034] Signal conditioning and acquisition module, used to process and convert sensor acquisition signals;

[0035] The microprocessor module controls the operation of each module and is used to calculate the oil level according to the ultrasonic propagation time and the multi-band weighted average algorithm; the oil level calculation result is corrected in combination with the transformer load data: according to the pre-established load-oil level correlation model, when the load changes, the corresponding change trend of the oil level is predicted, and the oil level is predicted according to the load-oil level correlation model, and the predicted value and the calculated oil level are weighted averaged to obtain a more accurate oil level estimation value;

[0036] An oil temperature-oil level change model is established and combined with a load-oil level correlation model to determine in real time whether the oil level change conforms to normal physical laws, including that when the oil temperature rises, the oil level should rise accordingly according to the principle of thermal expansion and contraction; when the load increases, the oil temperature rise may cause the oil level to rise. If the oil level change does not conform to the expected law, it is determined that there may be a false oil level.

[0037] Provide decision-making suggestions based on the type and severity of false oil level;

[0038] Wireless communication module, which realizes remote data transmission and transmits oil level data and related status information and decision suggestions to the background monitoring system;

[0039] A power management module for providing low-power battery power supply;

[0040] Background monitoring system, used to store, display and analyze oil level data.

[0041] Furthermore, the signal conditioning and acquisition module processes the ultrasonic echo signal according to a specific filter function to remove interference and improve the signal-to-noise ratio.

[0042] Furthermore, the microprocessor module is specifically used to measure the oil level height H using the ultrasonic propagation time after multi-band weighted averaging as shown in the following formula:

[0043]

[0044] H=H 总 -S 综合

[0045] S i =V×Δt / 2

[0046] In the formula, assume different frequencies f i Corresponding sensor to oil level distance S i , weight ω i , V is the ultrasonic wave propagation speed, transit time Δt = t 1 -t 0 ,t 1 is the time of receiving the echo, t 0 is the launch time, H 总 is the total height of the oil storage tank;

[0047] Oil temperature-oil level change model calculation oil temperature and load judgment temperature influence oil level H 温 As shown in the following formula:

[0048] H 温 =H 0 ×(1+α×ΔT)

[0049] In the formula, temperature compensation, assuming oil thermal expansion coefficient α, temperature change ΔT, initial test oil level H 0 :

[0050] The load-oil level correlation model establishes the relationship between load L and oil level change f(L) based on data statistics, and calculates the load impact on oil level H 负 :

[0051] H 负 =f(L).

[0052] Introducing comprehensive feature P 综合 The ultrasonic propagation time after multi-band weighted average is corrected to measure the oil level height H, where , g i is the fusion coefficient, P i The characteristics at different frequencies are the amplitude, phase or arrival time of the echo signal, and the corrected S 综合 for

[0053] Furthermore, the judgment logic for determining the possible existence of a false oil level is:

[0054] Set the oil temperature change rate threshold ΔT th and oil level change rate threshold ΔH th , when the oil temperature change rate exceeds ΔT th And the oil level change rate does not reach ΔH th When the load change rate exceeds the set threshold value and the oil level changes abnormally, it is determined to be a suspected false oil level. The historical data is compared and the oil level change trend is analyzed to confirm whether it is a false oil level.

[0055] When a false oil level is detected, a warning signal is issued, which is sent to the background monitoring system and triggers the sound and light alarm locally to alert the on-site operation and maintenance personnel.

[0056] The present invention has the following beneficial effects:

[0057] The present invention realizes high-precision oil level measurement, strong anti-interference, intelligent false oil level discrimination and real-time remote monitoring. Field tests show that the system can stably and accurately monitor in complex working conditions, effectively prevent abnormal oil level failures, improve transformer operation and maintenance efficiency and grid power supply reliability, and lay a solid foundation for the reliable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 is a system framework diagram provided by an embodiment of the present invention; DETAILED DESCRIPTION

[0059] See also Figure 1 As shown, an embodiment of the present invention provides an online monitoring system for oil level in a transformer oil storage cabinet based on ultrasonic technology.

[0060] It includes: a sensor module, including a multi-band ultrasonic sensor, a temperature sensor and a load sensor, which uses the multi-band ultrasonic sensor to transmit ultrasonic waves into the oil storage cabinet and receive echo signals reflected by the oil surface, and the temperature sensor and the load sensor respectively synchronously collect transformer oil temperature and load data;

[0061] Signal conditioning and acquisition module, used to process and convert sensor acquisition signals;

[0062] The microprocessor module controls the operation of each module and is used to calculate the oil level according to the ultrasonic propagation time and the multi-band weighted average algorithm; the oil level calculation result is corrected in combination with the transformer load data: according to the pre-established load-oil level correlation model, when the load changes, the corresponding change trend of the oil level is predicted, and the oil level is predicted according to the load-oil level correlation model, and the predicted value and the calculated oil level are weighted averaged to obtain a more accurate oil level estimation value;

[0063] An oil temperature-oil level change model is established and combined with a load-oil level correlation model to determine in real time whether the oil level change conforms to normal physical laws, including that when the oil temperature rises, the oil level should rise accordingly according to the principle of thermal expansion and contraction; when the load increases, the oil temperature rise may cause the oil level to rise. If the oil level change does not conform to the expected law, it is determined that there may be a false oil level.

[0064] Provide decision-making suggestions based on the type and severity of false oil level;

[0065] Wireless communication module, which realizes remote data transmission and transmits oil level data and related status information and decision suggestions to the background monitoring system;

[0066] A power management module for providing low-power battery power supply;

[0067] Background monitoring system, used to store, display and analyze oil level data.

[0068] The signal conditioning and acquisition module processes the ultrasonic echo signal according to a specific filter function to remove interference and improve the signal-to-noise ratio.

[0069] Among them, ultrasonic sensor installation and signal acquisition. Install a multi-band ultrasonic sensor on the transformer oil conservator, and choose the installation position on the side or top of the oil conservator to ensure that the ultrasonic wave can be incident vertically on the oil surface and avoid obstacles inside the oil conservator (such as baffles, pipes, etc.) and strong electromagnetic interference sources (such as transformer cores, windings, etc.). Fix the ultrasonic sensor with a special mounting bracket and ensure that it is in close contact with the oil conservator wall to ensure good acoustic coupling.

[0070] At the same time, a temperature sensor is installed on the transformer, which is closely attached to the wall of the oil tank or oil storage cabinet, to collect the temperature data of the transformer oil in real time; if the load data is obtained indirectly, the load information of the transformer is obtained through the corresponding electrical connection or communication interface.

[0071] The multi-band ultrasonic sensor transmits ultrasonic pulses into the oil storage tank according to the preset frequency sequence and time interval. For example, ultrasonic waves with frequencies of 30kHz, 50kHz, and 80kHz are transmitted in sequence every 5 seconds to meet the measurement requirements under different oil level heights and oil quality conditions. Under the precise control of the microprocessor, the transmitting circuit generates an electrical pulse signal of a specific frequency and amplitude, driving the piezoelectric element of the ultrasonic sensor to generate mechanical vibrations, thereby transmitting ultrasonic waves into the oil space inside the oil storage tank. During the propagation process, these ultrasonic waves will be reflected when they encounter the oil surface, and part of the energy will be reflected back to the sensor. The piezoelectric element of the sensor converts the mechanical vibration of the received reflected echo into an electrical signal, namely the echo signal.

[0072] Preferably, the ultrasonic sensor is installed with a waterproof, dustproof, and anti-interference housing design to ensure long-term stable operation in harsh outdoor environments. The housing material is a metal alloy with good electromagnetic shielding performance, such as aluminum alloy, and the interior is filled with absorbing materials to further reduce the impact of external electromagnetic interference on the sensor. A special acoustic coupling agent is used between the sensor and the oil storage cabinet wall to enhance the efficiency of sound wave propagation and improve signal quality.

[0073] The echo signal first enters the signal conditioning and acquisition module for preprocessing. The amplifier circuit amplifies the weak echo signal to increase its amplitude to a range suitable for subsequent processing. For example, a signal at the millivolt level is amplified to the volt level so that the subsequent analog-to-digital conversion can be quantified more accurately. The amplification factor is dynamically adjusted according to the strength of the sensor output signal and the requirements of the subsequent processing circuit to ensure that the signal is fully amplified without distortion.

[0074] The filter circuit uses a specially designed filter function to effectively filter out environmental noise, electromagnetic interference and other clutter signals according to the frequency characteristics of the ultrasonic signal. For example, a bandpass filter is used to allow only ultrasonic signals in a specific frequency band to pass through, suppressing interference signals in other frequency bands, thereby improving the signal-to-noise ratio of the signal. The filter parameters (such as center frequency, bandwidth, etc.) are optimized according to the frequency band of the ultrasonic sensor used and the actual interference situation to achieve the best filtering effect.

[0075] The analog signal after amplification and filtering is converted into a digital signal through an analog-to-digital converter. According to the sampling theorem, the sampling frequency (such as 100kHz, more than twice the highest frequency of the ultrasonic signal) and the number of quantization bits (such as 12 bits or 16 bits) are reasonably set to convert the continuous analog signal into a discrete digital signal so that the microprocessor can perform accurate calculations and processing. The selection of the sampling frequency must not only meet the sampling theorem, but also consider the real-time requirements and data processing capabilities of the system to ensure that the data can be quickly and effectively acquired and processed without affecting the measurement accuracy.

[0076] After receiving the digital signal, the microprocessor module accurately calculates the transit time Δt based on the time stamps of the transmitted and received echoes. The ultrasonic propagation velocity table at different temperatures pre-stored in the microprocessor (obtained through a large number of experimental calibrations) is used, combined with the oil temperature data collected in real time by the temperature sensor, to calculate the ultrasonic propagation velocity V at the current temperature. Then, according to the formula Calculate the distance from the sensor to the oil surface corresponding to each frequency band.

[0077] For example, when the temperature sensor detects that the oil temperature is 40°C, the corresponding ultrasonic propagation velocity correction coefficient (such as 1.02, assuming that the sound velocity at normal temperature is v 0 , the temperature coefficient is k, then v = v 0 (1+kΔT)=v 0 (1+k×(40-25)), where 25°C is room temperature), to compensate for the calculation.

[0078] The multi-band weighted average algorithm is used to calculate the final oil level height H. According to the measurement stability and accuracy of different frequency bands under different working conditions, each frequency band is assigned a corresponding weight w.i For example, when the oil temperature is high and the oil is dirty, through experiments and data analysis, it is found that the measurement results of the low frequency band (such as 30kHz) are less affected, and its weight can be appropriately increased (such as 0.4), and the measurement results of the high frequency band (such as 80kHz) are greatly affected, and its weight can be reduced (such as 0.2). The weight of the middle frequency band (such as 50kHz) is set to 0.4. Through the formula The final oil level height H is calculated.

[0079] Furthermore, the oil level calculation result is corrected in combination with the transformer load data. According to the pre-established load-oil level correlation model, when the load changes, the corresponding change trend of the oil level is predicted, and the calculated oil level height is dynamically adjusted. For example, when the load increases by 10%, the model predicts that the oil level may rise by 5mm. This predicted value is weighted averaged with the oil level height calculated based on ultrasonic measurement to obtain a more accurate oil level estimate.

[0080] The microprocessor continuously monitors the oil level changes and conducts comprehensive analysis based on the data from the temperature sensor and the load sensor (which obtains data indirectly). By establishing the oil temperature-oil level change model and the load-oil level correlation model, it is possible to determine in real time whether the oil level changes conform to normal physical laws. For example, when the oil temperature rises, the oil level should rise accordingly based on the principle of thermal expansion and contraction; when the load increases, the oil temperature rise may cause the oil level to rise. If the oil level changes do not conform to these expected laws, it is determined that there may be a false oil level.

[0081] The specific judgment logic is as follows: Set the oil temperature change rate threshold ΔT th (such as 0.5℃ / min) and oil level change rate threshold ΔH th (e.g. 2mm / min). When the oil temperature change rate exceeds ΔT th And the oil level change rate does not reach ΔH th When the load change rate exceeds a certain value (such as 15%) and the oil level changes abnormally, it is determined to be a suspected false oil level. At this time, the microprocessor starts further diagnostic procedures, such as comparing historical data, analyzing oil level change trends, etc., to confirm whether it is a false oil level.

[0082] When a false oil level is detected, the microprocessor immediately sends out a warning signal, which can be sent to the background monitoring system through the wireless communication module, and at the same time trigger the sound and light alarm locally to remind the on-site operation and maintenance personnel. For example, when it is determined to be a false oil level, the red warning light on the scene lights up, the buzzer sounds an alarm, and the background monitoring system pops up a striking alarm message, showing the specific transformer number, location and abnormal oil level data, so that the operation and maintenance personnel can take timely measures to investigate and deal with it.

[0083] In addition, the microprocessor provides corresponding intelligent decision-making suggestions based on the type and severity of the false oil level. For example, if the false oil level alarm is caused by a faulty oil temperature sensor, it is recommended that the operation and maintenance personnel check the oil temperature sensor and its connection lines; if the abnormal drop in oil level is caused by possible internal leakage, it is recommended to immediately arrange a power outage for maintenance and check the internal sealing of the transformer.

[0084] Data transmission and remote monitoring:

[0085] The calculated oil level data, oil temperature data, load data (if any), and system operation status information are transmitted through the stable transmission link constructed by the wireless networking unit of the wireless communication module. The wireless communication module uses low-power, high-reliability communication technology, such as LoRa technology, to send data to the data remote receiving unit.

[0086] LoRa technology has the advantages of long-distance transmission (up to several kilometers), low power consumption (long-term operation under battery power), strong anti-interference ability (using spread spectrum communication technology), etc. It is suitable for the complex electromagnetic environment and long-distance data transmission requirements in transformer monitoring scenarios. During the transmission process, the data is encrypted to ensure the security and integrity of the data and prevent the data from being stolen or tampered with.

[0087] The data remote receiving unit transmits the received data to the data receiving and storage server of the background monitoring system through communication networks such as Ethernet, GPRS or 4G / 5G. The server stores the received data in a database, which has complete data management functions, including data storage, query, backup and recovery, so as to preserve a large amount of historical data for a long time and provide solid data support for subsequent data analysis and fault diagnosis.

[0088] The display and analysis platform of the background monitoring system uses an intuitive user interface to display the real-time change trend of oil level data, historical data records, and the correlation with parameters such as oil temperature and load. For example, a line graph is used to display the change curve of oil level over time in the past 24 hours, while a bar graph is used to compare the impact of oil temperature changes on oil level in different time periods, and a scatter plot is used to analyze the correlation between load changes and oil level fluctuations.

[0089] The platform has data analysis functions, such as data mining and trend prediction. Through in-depth analysis of historical data and real-time monitoring data, the changing trend of transformer oil level is predicted. For example, based on the changing patterns of oil temperature, load and oil level data in the past week, a time series analysis algorithm (such as the ARIMA model) is used to predict the possible range of oil level changes in the next few days. When it is predicted that the oil level may exceed the normal range or fluctuate abnormally, early warning information is issued in advance to assist operation and maintenance personnel in formulating reasonable operation and maintenance strategies, such as arranging inspections in advance, adjusting loads, or preparing to replenish transformer oil.

[0090] At the same time, big data analysis technology is used to conduct a comprehensive analysis of the monitoring data of multiple transformers to explore potential failure modes and related factors. For example, if a batch of transformers is found to be prone to abnormal oil level fluctuations under specific load and oil temperature conditions, relevant departments will be notified in a timely manner to focus on and evaluate the batch of transformers, and recall or upgrade them when necessary, thereby improving the reliability and stability of the power system.

[0091] Another embodiment of the present invention provides an online monitoring method for oil level in a transformer oil conservator based on ultrasonic technology, comprising the following steps:

[0092] Step 1: Use a multi-band ultrasonic sensor to transmit ultrasonic waves into the oil storage tank and receive echo signals reflected from the oil surface;

[0093] Step 2, synchronously collect transformer oil temperature and load data;

[0094] Step 3, calculating the oil level height based on ultrasonic propagation time and multi-band weighted average algorithm;

[0095] Step 4, correct the oil level calculation result in combination with the transformer load data: according to the pre-established load-oil level correlation model, when the load changes, predict the corresponding change trend of the oil level, predict the oil level according to the load-oil level correlation model, and perform weighted average of the predicted value and the calculated oil level height to obtain a more accurate oil level estimate;

[0096] Step 5: Establish an oil temperature-oil level change model and combine it with a load-oil level correlation model to determine in real time whether the oil level change conforms to normal physical laws, including that when the oil temperature rises, the oil level should rise accordingly according to the principle of thermal expansion and contraction; when the load increases, the oil temperature rise may cause the oil level to rise. If the oil level change does not conform to the expected law, it is determined that there may be a false oil level.

[0097] Step 6: Provide decision suggestions based on the type and severity of the false oil level.

[0098] Step 7: Remotely transmit the oil level data and related status information and decision recommendations to the background monitoring system.

[0099] Further, step 3 specifically includes: including:

[0100] The ultrasonic propagation time after multi-band weighted averaging measures the oil level height H as shown in the following formula:

[0101]

[0102] H=H 总 -S 综合

[0103] S i =V×Δt / 2

[0104] In the formula, assume different frequencies f i Corresponding sensor to oil level distance S i , weight ω i , V is the ultrasonic wave propagation speed, transit time Δt = t 1 -t 0 ,t 1 is the time of receiving the echo, t 0 is the launch time, H 总 is the total height of the oil storage tank.

[0105] Oil temperature-oil level change model calculation oil temperature and load judgment temperature influence oil level H 温 As shown in the following formula:

[0106] H 温 =H 0 ×(1+α×ΔT)

[0107] In the formula, temperature compensation, assuming oil thermal expansion coefficient α, temperature change ΔT, initial test oil level H 0 :

[0108] The load-oil level correlation model establishes the relationship between load L and oil level change f(L) based on data statistics, and calculates the load impact on oil level H 负 :

[0109] H 负 =f(L).

[0110] Furthermore, the comprehensive feature P is introduced 综合 The ultrasonic propagation time after multi-band weighted average is corrected to measure the oil level height H, where , g i is the fusion coefficient, P i The characteristics at different frequencies are the amplitude, phase or arrival time of the echo signal, and the corrected S 综合 for

[0111]

[0112] Furthermore, the multi-band ultrasonic sensor is installed on the side or top of the oil storage tank to ensure that the ultrasonic wave is incident vertically on the oil surface and avoids the strong electromagnetic interference area; the multi-band ultrasonic sensor emits ultrasonic pulses into the oil storage tank according to a preset frequency sequence and time interval.

[0113] After amplification and filtering, the echo signal is converted into a digital signal. The transit time Δt is calculated based on the time stamps of the transmitted and received echoes. The ultrasonic propagation velocity table at different temperatures pre-stored in the microprocessor is used, combined with the oil temperature data collected in real time by the temperature sensor, to calculate the ultrasonic propagation velocity V at the current temperature.

[0114] The judgment logic for determining the possible existence of false oil level is:

[0115] Set the oil temperature change rate threshold ΔT th and oil level change rate threshold ΔH th , when the oil temperature change rate exceeds ΔT th And the oil level change rate does not reach ΔH th When the load change rate exceeds the set threshold value and the oil level changes abnormally, it is determined to be a suspected false oil level. The historical data is compared and the oil level change trend is analyzed to confirm whether it is a false oil level.

[0116] When a false oil level is detected, a warning signal is issued, which is sent to the background monitoring system and triggers the sound and light alarm locally to alert the on-site operation and maintenance personnel.

[0117] The signal conditioning and acquisition module amplifies, filters, and performs analog-to-digital conversion on ultrasonic echo, temperature, and load signals. The ultrasonic echo signal processing is shown in the following formula:

[0118] y(t)=F(x(t))

[0119] In the formula, filtering (assuming filter function F, original signal x(t)) is used to remove interference.

[0120] Analog-to-digital conversion (analog signal y(t), sampling frequency f s , quantization bit number n), according to the sampling theorem:

[0121] f s ≥2f max

[0122] In the formula, f max is the highest frequency of the signal, and the digital signal D[k] represents the sampling value.

[0123] The time delay between the transmitted signal s(t) and the received signal r(t) is determined by the cross-correlation algorithm:

[0124]

[0125] In the formula, the cross-correlation algorithm (assuming the transmitted signal is s(t) and the received signal is r(t)), the τ value is the transit time between the transmitted signal and the received signal, that is, the time Δt from the transmission to the reception of the ultrasonic wave. The transit time Δt is determined by the peak value and substituted into the oil level formula for calculation.

[0126] Introducing multi-band feature fusion (different frequency features P i )The comprehensive characteristics are shown in the following formula:

[0127]

[0128] In the formula, g i is the fusion coefficient, which assists in oil level calculation.

[0129] In the formula, g i is the fusion coefficient, which assists in oil level calculation, P i (i=1, 2, 3 represent the relevant parameters of time, temperature and load at different frequencies respectively) The time parameter reflects the time characteristics of ultrasonic waves of different frequencies during the propagation process, the temperature parameter reflects the influence of the change of ultrasonic propagation speed of each frequency under different oil temperature conditions on the measurement, and the load parameter represents the relevant changes of ultrasonic oil level measurement of different frequencies when the transformer load changes.

[0130] Assume there are three different frequencies f 1 、f 2 、f 3 The corresponding features of the ultrasonic echo signal are A 1 , A 2 , A 3 (The features can be the amplitude, phase, arrival time, etc. of the echo signal), and the fusion coefficients are α 1 , α 2 , α 3 .

[0131] Comprehensive characteristics

[0132] P (综合) =α 1 ×A 1 +α 2 ×A 2 +α 3 ×A 3

[0133] This comprehensive feature P (综合) Substitute into the oil level calculation formula, H = Htotal-S 综 combine,

[0134]

[0135] The present invention combines the characteristics P of different frequencies iAccording to their corresponding fusion coefficient g i Perform weighted summation to obtain the comprehensive feature P (综合) This comprehensive feature can integrate the advantages of ultrasonic echo signals of different frequencies and make up for the shortcomings that may exist in single frequency measurement, so that the final calculated oil level value is more accurate and reliable, and the accuracy of the entire oil level online monitoring system for oil level judgment is improved, so as to better provide effective monitoring data support for the safe and stable operation of the transformer.

Claims

1. A method for online monitoring of oil level in a transformer oil storage cabinet based on ultrasonic technology, characterized in that: The following steps are involved: Step 1: Use a multi-band ultrasonic sensor to transmit ultrasonic waves into the oil storage tank and receive echo signals reflected from the oil surface; Step 2, synchronously collect transformer oil temperature and load data; Step 3, calculating the oil level height based on ultrasonic propagation time and multi-band weighted average algorithm; Step 4, correct the oil level calculation result in combination with the transformer load data: according to the pre-established load-oil level correlation model, when the load changes, predict the corresponding change trend of the oil level, predict the oil level according to the load-oil level correlation model, and perform weighted average of the predicted value and the calculated oil level height to obtain a more accurate oil level estimate; Step 5: Establish an oil temperature-oil level change model and combine it with a load-oil level correlation model to determine in real time whether the oil level change conforms to normal physical laws, including that when the oil temperature rises, the oil level should rise accordingly according to the principle of thermal expansion and contraction; when the load increases, the oil temperature rise may cause the oil level to rise. If the oil level change does not conform to the expected law, it is determined that there may be a false oil level. Step 6: Provide decision suggestions based on the type and severity of the false oil level. Step 7: Remotely transmit the oil level data and related status information and decision recommendations to the background monitoring system.

2. The method for online monitoring oil level of a transformer oil storage cabinet based on ultrasonic technology according to claim 1 is characterized in that: Step 3 specifically includes: The ultrasonic propagation time after multi-band weighted averaging measures the oil level height H as shown in the following formula: H=H 总 -S 综合 S i =V×Δt / 2 In the formula, assume different frequencies f i Corresponding sensor to oil level distance S i , weight ω i , V is the ultrasonic wave propagation speed, transit time Δt=t1-t0, t1 is the time of receiving echo, t0 is the time of transmitting, H 总 is the total height of the oil storage tank.

3. The method for online monitoring oil level of a transformer oil storage cabinet based on ultrasonic technology according to claim 1 is characterized in that: Oil temperature-oil level change model calculation oil temperature and load judgment temperature influence oil level H 温 As shown in the following formula: H 温 =H0×(1+α×ΔT) In the formula, temperature compensation, assuming oil thermal expansion coefficient α, temperature change ΔT, initial test oil level H0: The load-oil level correlation model establishes the relationship between load L and oil level change f(L) based on data statistics, and calculates the load impact on oil level H 负 : H 负 =f(L)。 4. The method for online monitoring oil level of a transformer oil storage cabinet based on ultrasonic technology according to claim 2 is characterized in that: Introducing comprehensive feature P 综合 The ultrasonic propagation time after multi-band weighted average is corrected to measure the oil level height H, where g i is the fusion coefficient, P i The characteristics at different frequencies are the amplitude, phase or arrival time of the echo signal, and the corrected S 综合 for 5. The method for online monitoring oil level of a transformer oil storage cabinet based on ultrasonic technology according to claim 1 is characterized in that: The multi-band ultrasonic sensor is installed on the side or top of the oil storage tank to ensure that the ultrasonic wave is incident on the oil surface vertically and avoids the strong electromagnetic interference area; the multi-band ultrasonic sensor emits ultrasonic pulses into the oil storage tank according to the preset frequency sequence and time interval.

6. The method for online monitoring oil level of a transformer oil storage cabinet based on ultrasonic technology according to claim 2 is characterized in that: After amplification and filtering, the echo signal is converted into a digital signal. The transit time Δt is calculated based on the time stamps of the transmitted and received echoes. The ultrasonic propagation velocity table at different temperatures pre-stored in the microprocessor is used, combined with the oil temperature data collected in real time by the temperature sensor, to calculate the ultrasonic propagation velocity V at the current temperature.

7. The method for online monitoring oil level of a transformer oil storage cabinet based on ultrasonic technology according to claim 1 is characterized in that: The judgment logic for determining the possible existence of false oil level is: Set the oil temperature change rate threshold ΔT th and oil level change rate threshold ΔH th , when the oil temperature change rate exceeds ΔT th And the oil level change rate does not reach ΔH th When the load change rate exceeds the set threshold value and the oil level changes abnormally, it is determined to be a suspected false oil level. The historical data is compared and the oil level change trend is analyzed to confirm whether it is a false oil level. When a false oil level is detected, a warning signal is issued, which is sent to the background monitoring system and triggers the sound and light alarm locally to alert the on-site operation and maintenance personnel.

8. An online monitoring system for oil level in transformer oil storage cabinet based on ultrasonic technology. It is characterized in that It includes: a sensor module, including a multi-band ultrasonic sensor, a temperature sensor and a load sensor, which uses the multi-band ultrasonic sensor to transmit ultrasonic waves into the oil storage cabinet and receive echo signals reflected by the oil surface, and the temperature sensor and the load sensor respectively synchronously collect transformer oil temperature and load data; Signal conditioning and acquisition module, used to process and convert sensor acquisition signals; The microprocessor module controls the operation of each module and is used to calculate the oil level according to the ultrasonic propagation time and the multi-band weighted average algorithm; the oil level calculation result is corrected in combination with the transformer load data: according to the pre-established load-oil level correlation model, when the load changes, the corresponding change trend of the oil level is predicted, and the oil level is predicted according to the load-oil level correlation model, and the predicted value and the calculated oil level are weighted averaged to obtain a more accurate oil level estimation value; An oil temperature-oil level change model is established and combined with a load-oil level correlation model to determine in real time whether the oil level change conforms to normal physical laws, including that when the oil temperature rises, the oil level should rise accordingly according to the principle of thermal expansion and contraction; when the load increases, the oil temperature rise may cause the oil level to rise. If the oil level change does not conform to the expected law, it is determined that there may be a false oil level. Provide decision-making suggestions based on the type and severity of false oil level; Wireless communication module, which realizes remote data transmission and transmits oil level data and related status information and decision suggestions to the background monitoring system; A power management module for providing low-power battery power supply; Background monitoring system, used to store, display and analyze oil level data.

9. The transformer oil storage tank oil level online monitoring system based on ultrasonic technology according to claim 8 is characterized in that: The signal conditioning and acquisition module processes the ultrasonic echo signal according to a specific filter function to remove interference and improve the signal-to-noise ratio; The microprocessor module is specifically used to measure the oil level H by ultrasonic propagation time after multi-band weighted averaging as shown in the following formula: H=H 总 -S 综合 S i =V×Δt / 2 In the formula, assume different frequencies f i Corresponding sensor to oil level distance S i , weight ω i , V is the ultrasonic wave propagation speed, transit time Δt=t1-t0, t1 is the time of receiving echo, t0 is the time of transmitting, H 总 is the total height of the oil storage tank; Oil temperature-oil level change model calculation oil temperature and load judgment temperature influence oil level H 温 As shown in the following formula: H 温 =H0×(1+α×ΔT) In the formula, temperature compensation, assuming oil thermal expansion coefficient α, temperature change ΔT, initial test oil level H0: The load-oil level correlation model establishes the relationship between load L and oil level change f(L) based on data statistics, and calculates the load impact on oil level H 负 : H 负 =f(L); Introducing comprehensive feature P 综合 The ultrasonic propagation time after multi-band weighted average is corrected to measure the oil level height H, where g i is the fusion coefficient, P i The characteristics at different frequencies are the amplitude, phase or arrival time of the echo signal, and the corrected S 综合 for 10. The method for online monitoring oil level of a transformer oil conservator based on ultrasonic technology according to claim 9 is characterized in that: The judgment logic for determining the possible existence of false oil level is: Set the oil temperature change rate threshold ΔT th and oil level change rate threshold ΔH th , when the oil temperature change rate exceeds ΔT th And the oil level change rate does not reach ΔH th When the load change rate exceeds the set threshold value and the oil level changes abnormally, it is determined to be a suspected false oil level. The historical data is compared and the oil level change trend is analyzed to confirm whether it is a false oil level. When a false oil level is detected, a warning signal is issued, which is sent to the background monitoring system and triggers the sound and light alarm locally to alert the on-site operation and maintenance personnel.

Images