Non-contact detection system and method for water content in transformer oil by single ultrasonic probe

Abstract

The application discloses a kind of single ultrasonic probe transformer oil water content non-contact detection system and method, it is related to transformer oil detection technical field.The system includes single ultrasonic sensor, first substrate, cavity, second substrate and signal acquisition and processing unit;The sensor is placed outside first substrate, and the ultrasonic wave of emission enters oil sample through first substrate, and first interface reflection echo is generated at the interface of first substrate and oil sample, and second interface reflection echo is generated at the interface of oil sample and second substrate;Signal acquisition and processing unit calculate the acoustic impedance of oil sample according to the root mean square value of voltage of first interface reflection echo, calculate the sound velocity according to the time difference of two reflection echoes, calculate the density according to the ratio of acoustic impedance and sound velocity, and fuse three parameters to retrieve water content.The application uses single-probe pulse echo mode, realizes non-contact measurement at the same time, synchronously acquires multiple independent acoustic parameters, effectively improves the accuracy of water content detection, and is suitable for real-time online monitoring of transformer oil water content.

Description

Technical Field

[0001] This invention relates to the field of transformer oil testing technology, and more specifically, to a non-contact testing system and method for transformer oil water content using a single ultrasonic probe. Background Technology

[0002] Transformer oil is a crucial medium in oil-immersed power transformers, serving both insulation and heat dissipation functions. During long-term operation, the oil-paper insulation system continuously withstands electrical, thermal, and chemical stresses. Moisture is one of the most significant contaminants affecting the insulation performance of transformer oil. The presence of even trace amounts of water in transformer oil can significantly reduce its breakdown voltage, accelerate the aging of the oil-paper insulation system, and induce bubble formation at high temperatures, potentially leading to insulation breakdown and transformer burnout in severe cases. Therefore, accurate detection of water content in transformer oil is of paramount importance for ensuring the safe and stable operation of power equipment.

[0003] Currently, the main methods for detecting water content in transformer oil include offline chemical analysis, capacitive sensing, and fiber optic sensing. Karl Fischer titration is a representative offline chemical analysis method, offering high accuracy and water specificity. However, this method requires offline sampling, which is cumbersome, time-consuming, and consumes chemical reagents, making real-time online monitoring impossible. Capacitive sensing utilizes the characteristic that the capacitance of a moisture-sensitive material changes with water content, enabling online monitoring. However, the sensor must be directly immersed in the oil, making it susceptible to contamination from sludge and aging products over long-term operation, leading to measurement drift and hysteresis. Furthermore, its sensitivity is relatively low and it is susceptible to electromagnetic interference. Fiber optic sensing offers advantages in resisting electromagnetic interference, but the sensor manufacturing process is complex, and the sensitive coating is prone to swelling or corrosion degradation after long-term immersion in oil, resulting in a high detection limit that fails to meet the requirements for high-precision measurement.

[0004] Ultrasonic testing technology has advantages such as being non-invasive and having strong penetrating power, and has been applied to the detection of trace water content in transformer oil. Existing ultrasonic solutions mostly employ a dual-probe transmission measurement structure, requiring the transmitting and receiving probes to be strictly coaxially aligned, which is difficult to install and susceptible to vibration; the sensor's direct contact with the oil also poses a risk of contamination. Furthermore, the dual-probe transmission method mainly uses the flight time of the direct wave to calculate the sound velocity, making it difficult to simultaneously obtain multi-dimensional acoustic parameters such as acoustic impedance and density in a single measurement; and the ability of a single sound velocity parameter to characterize water content is limited.

[0005] Therefore, how to achieve high-precision multi-parameter synchronous measurement with a simplified hardware structure without contacting transformer oil is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To overcome the problem that existing detection methods cannot achieve high-precision measurement with a simplified structure without contacting the oil, this invention provides a non-contact detection system and method for transformer oil water content using a single ultrasonic probe.

[0007] The technical solution of this invention is as follows:

[0008] A non-contact detection system for transformer oil moisture content using a single ultrasonic probe includes:

[0009] A single ultrasonic sensor is used to emit ultrasonic pulses and receive echo signals.

[0010] A first substrate is disposed between the single ultrasonic sensor and the transformer oil to be tested. The single ultrasonic sensor is disposed on the outside of the first substrate. It transmits ultrasonic pulses to the transformer oil to be tested through the first substrate and receives the first interface reflected echo from the interface between the first substrate and the transformer oil to be tested.

[0011] A cavity for containing the transformer oil to be tested, one end of which is closed by the first substrate;

[0012] The second substrate is disposed at the other end of the cavity and serves as an ultrasonic reflective surface to generate a second interface reflected echo between the transformer oil under test and the second substrate.

[0013] The signal acquisition and processing unit is used to acquire the echo signal received by the single ultrasonic sensor, and calculate the acoustic impedance, sound velocity and density of the transformer oil under test based on the first interface reflected echo and the second interface reflected echo, and then invert the water content.

[0014] Preferably, the signal acquisition and processing unit includes:

[0015] The acoustic impedance calculation module is used to calculate the acoustic impedance of the transformer oil under test based on the root mean square voltage value of the reflected echo from the first interface.

[0016] The sound velocity calculation module is used to calculate the sound velocity of the transformer oil under test based on the time difference between the reflected echo from the first interface and the reflected echo from the second interface.

[0017] The density calculation module is used to calculate the density of the transformer oil to be tested based on the ratio of the acoustic impedance to the sound velocity.

[0018] The water content inversion module is used to invert the water content of the transformer oil under test based on the mapping relationship between acoustic impedance, sound velocity, density and water content.

[0019] Preferably, the acoustic impedance calculation module uses a relative measurement method to calculate the acoustic impedance of the transformer oil under test:

[0020] ;

[0021] The intermediate variable K is:

[0022] ;

[0023] In the formula, The acoustic impedance of the transformer oil to be tested. Let be the acoustic impedance of the first substrate. As a reference liquid, The intensity of the reflected echo signal from the first interface of the transformer oil under test. The reflected echo signal intensity of the ultrasonic wave at the interface between the first substrate and the reference liquid is represented by the root mean square voltage value.

[0024] Preferably, the sound velocity calculation module uses a cross-correlation algorithm to calculate the time difference between the echo reflected from the first interface and the echo reflected from the second interface:

[0025] ;

[0026] In the formula, The signal reflected from the first interface. The signal reflected from the second interface. For time-delay variables, find the cross-correlation function. The peak position determines the time difference, and the speed of sound is calculated according to the following formula:

[0027] ;

[0028] The velocity of sound in the transformer oil to be tested. The thickness of the transformer oil to be measured in the cavity. The time difference is mentioned.

[0029] Preferably, the cavity includes a first chamber and a second chamber arranged side by side, the first chamber being used to contain a reference liquid and the second chamber being used to contain the transformer oil to be tested; the single ultrasonic sensor performs measurements sequentially above the first chamber and the second chamber to achieve real-time calibration of the reference signal and the target signal.

[0030] Preferably, the reference liquid is any one of pure water, ethanol, or standard silicone oil, or a solid block with known acoustic impedance is used as a calibration reference.

[0031] Preferably, the material of the first substrate is a material with uniform acoustic impedance and isotropic, selected from any one of acrylic, glass, polycarbonate, polyetheretherketone, epoxy resin, quartz glass or ceramic.

[0032] Preferably, it also includes a temperature sensor and a temperature compensation module. The temperature sensor is used to detect the real-time temperature of the transformer oil under test, and the temperature compensation module is used to perform temperature correction on the sound velocity and / or acoustic impedance based on the real-time temperature.

[0033] Preferably, the single ultrasonic sensor is replaced by an ultrasonic phased array probe or a multi-point matrix probe to simultaneously monitor the water content distribution at different spatial locations.

[0034] A second aspect of the present invention also provides a non-contact detection method for water content in transformer oil based on a single ultrasonic probe, comprising the following steps:

[0035] S1. A single ultrasonic sensor is placed on the outside of the first substrate, so that the ultrasonic pulse enters the transformer oil to be tested in the cavity through the first substrate, and is partially reflected and partially transmitted at the interface between the first substrate and the transformer oil to be tested, generating a first interface reflected echo.

[0036] S2. The transmitted wave propagates in the transformer oil under test to the interface between the second substrate and the transformer oil under test, where it is reflected to generate a second interface reflected echo.

[0037] S3. Receive the first interface reflected echo and the second interface reflected echo through the single ultrasonic sensor.

[0038] S4. Calculate the acoustic impedance of the transformer oil under test based on the reflected echo from the first interface;

[0039] S5. Calculate the sound velocity of the transformer oil under test based on the time difference between the reflected echo from the first interface and the reflected echo from the second interface.

[0040] S6. Calculate the density of the transformer oil to be tested based on the ratio of the acoustic impedance to the sound velocity;

[0041] S7. The water content of the transformer oil to be tested is inverted based on the mapping relationship between acoustic impedance, sound velocity, density and water content.

[0042] According to the above-described solution, the beneficial effects of this invention are as follows:

[0043] 1. This invention uses a single ultrasonic sensor to work in pulse echo mode. Compared with the existing dual-probe transmission scheme, it does not require strict coaxial alignment of the transmitting and receiving probes, which physically eliminates the impact of alignment deviation on measurement accuracy and greatly reduces the hardware cost of the system and the difficulty of on-site installation and maintenance.

[0044] 2. The present invention isolates the ultrasonic sensor from the transformer oil to be tested through the first substrate. The sensor does not directly contact the oil, which avoids the contamination and corrosion of the sensor piezoelectric crystal by impurities and sludge in the transformer oil, and also prevents the potential contamination of the oil sample by the sensor, which is conducive to long-term stable operation.

[0045] 3. This invention can simultaneously acquire three independent acoustic parameters of transformer oil—sound velocity, acoustic impedance, and density—within a single measurement cycle. Compared to existing dual-probe transmission methods that rely solely on a single sound velocity parameter for water content determination, the fusion of these three parameters effectively distinguishes the influence of water content changes on acoustic characteristics from factors such as oil aging and temperature fluctuations, significantly improving the accuracy and anti-interference capability of water content detection.

[0046] 4. The present invention uses the root mean square voltage value as the characterization parameter of the reflected echo signal intensity. Compared with the traditional peak-to-peak voltage, the root mean square voltage value has better energy integration characteristics and stability when the signal-to-noise ratio is low or the waveform is slightly distorted, and has higher resolution for trace moisture changes (such as the range of 8ppm to 33ppm).

[0047] 5. This invention uses a cross-correlation function to calculate the time difference between the reflected echo from the first interface and the reflected echo from the second interface. Compared with the traditional threshold method or zero-crossing method, the cross-correlation algorithm has stronger noise resistance and a time resolution of up to nanosecond level, thus ensuring high accuracy of sound velocity measurement.

[0048] 6. By using a first chamber and a second chamber arranged in parallel, this invention can perform real-time calibration of the system in the same measurement process using a reference liquid with known acoustic properties, effectively eliminating system errors caused by sensor aging or temperature drift. At the same time, through the cooperation of a temperature sensor and a temperature compensation module, software correction of temperature-acoustic parameters can be achieved, reducing the system's dependence on hardware constant temperature conditions and enhancing its adaptability to industrial environments. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a schematic diagram of the non-contact detection system for transformer oil moisture content provided in an embodiment of the present invention.

[0051] Figure 2 This is a schematic diagram of the non-contact detection method for transformer oil water content provided in an embodiment of the present invention. Detailed Implementation

[0052] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0053] It should be noted that when a component is referred to as "fixed," "set," or "connected" to another component, it may be located directly or indirectly on that other component. The terms "upper," "lower," "left," "right," "front," "rear," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or position based on the accompanying drawings, and are for ease of description only, and should not be construed as limiting the technical solution. The terms "first," "second," etc., are used for ease of description only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. "Many" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0054] This invention provides a non-contact detection system for transformer oil moisture content based on a single ultrasonic probe. (See also...) Figure 1 The system includes a single ultrasonic sensor, a first substrate, a cavity, a second substrate, and a signal acquisition and processing unit. The single ultrasonic sensor emits ultrasonic pulses and receives echo signals. The first substrate is disposed between the single ultrasonic sensor and the transformer oil to be tested, with the single ultrasonic sensor located outside the first substrate. It emits ultrasonic pulses to the transformer oil through the first substrate and receives a first interface reflection echo from the interface between the first substrate and the transformer oil. The cavity contains the transformer oil to be tested, with one end closed by the first substrate. The second substrate is disposed at the other end of the cavity, serving as an ultrasonic reflector surface to generate a second interface reflection echo from the interface between the transformer oil and the second substrate. The signal acquisition and processing unit acquires the echo signals received by the single ultrasonic sensor and calculates the acoustic impedance, sound velocity, and density of the transformer oil based on the first and second interface reflection echoes, thereby determining the water content.

[0055] Specifically, the cavity includes a first chamber and a second chamber arranged side-by-side. The first chamber contains a reference liquid, and the second chamber contains the transformer oil to be tested. The single ultrasonic sensor performs measurements sequentially above the first and second chambers to achieve real-time calibration of the reference signal and the target signal. This invention, through the parallel arrangement of the first and second chambers, enables real-time system calibration using a reference liquid with known acoustic properties within the same measurement process, effectively eliminating system errors caused by sensor aging or temperature drift.

[0056] In this embodiment of the invention, the signal acquisition and processing unit includes an acoustic impedance calculation module, a sound velocity calculation module, a density calculation module, and a water content inversion module. The acoustic impedance calculation module calculates the acoustic impedance of the transformer oil under test based on the root mean square voltage (Vrms) of the reflected echo from the first interface; the sound velocity calculation module calculates the sound velocity of the transformer oil under test based on the time difference between the reflected echo from the first interface and the reflected echo from the second interface; the density calculation module calculates the density of the transformer oil under test based on the ratio of the acoustic impedance to the sound velocity; and the water content inversion module inverts the water content of the transformer oil under test based on the mapping relationship between the acoustic impedance, sound velocity, density, and water content.

[0057] In fact, this invention obtains three independent acoustic parameters of transformer oil—sound velocity, acoustic impedance, and density—within a single measurement cycle. Compared to the existing dual-probe transmission method that relies on only a single sound velocity parameter for water content determination, the fusion of these three parameters can effectively distinguish the influence of water content changes on acoustic characteristics, as well as factors such as oil aging and temperature fluctuations. This significantly improves the accuracy and anti-interference capability of water content detection.

[0058] Specifically, the acoustic impedance calculation module uses a relative measurement method to calculate the acoustic impedance of the transformer oil under test. The reflection coefficient of ultrasound at the interface satisfies:

[0059] ;

[0060] ;

[0061] In the formula, For the incident wave signal intensity, combine the above two equations to eliminate... ,get:

[0062] ;

[0063] in:

[0064] ;

[0065] In the formula, The acoustic impedance of the transformer oil to be tested. Let be the acoustic impedance of the first substrate. As a reference liquid, The intensity of the reflected echo signal from the first interface of the transformer oil under test. The reflected echo signal intensity of the ultrasonic wave at the interface between the first substrate and the reference liquid is represented by the root mean square voltage value.

[0066] In fact, this invention uses the root mean square voltage value as a characterization parameter of the reflected echo signal intensity. Compared with the traditional peak-to-peak voltage, the Vrms value has better energy integration characteristics and stability at low signal-to-noise ratios or with slight waveform distortion, and has higher resolution for trace moisture changes (such as the range of 8ppm to 33ppm).

[0067] Furthermore, the sound speed calculation module uses a cross-correlation algorithm to calculate the time difference between the echo reflected from the first interface and the echo reflected from the second interface:

[0068] ;

[0069] In the formula, The signal reflected from the first interface. The signal reflected from the second interface. For time-delay variables, find the cross-correlation function. The peak position determines the time difference, and the speed of sound is calculated according to the following formula:

[0070] ;

[0071] The velocity of sound in the transformer oil to be tested. The thickness of the transformer oil to be measured in the cavity. The time difference is given. The time difference is calculated using a cross-correlation function. Compared to traditional thresholding or zero-crossing methods, the cross-correlation algorithm has stronger noise resistance and a time resolution down to the nanosecond level, thus ensuring high accuracy in sound velocity measurement.

[0072] In this embodiment of the invention, the first substrate is made of a material with uniform acoustic impedance and isotropic, selected from any one of acrylic, glass, polycarbonate, polyetheretherketone, epoxy resin, quartz glass, or ceramic. Preferably, the first substrate is an acrylic sheet with a thickness of 3mm, 5mm, or 8mm, or a glass sheet with a thickness of 3mm. In particular, the first substrate must strictly eliminate materials with internal inhomogeneity. For example, some ordinary glass with a thickness of 5mm may cause aberrations and wavefront distortion in the ultrasonic beam during transmission due to internal anisotropy, so that the amplitude of the reflected echo is no longer simply determined by the interface reflection coefficient, thereby seriously affecting the measurement accuracy.

[0073] In this embodiment of the invention, the reference liquid is any one of pure water, ethanol, and standard silicone oil, or a solid block with known acoustic impedance can be used as a calibration reference. Preferably, this application uses pure water as the reference liquid, whose acoustic impedance at 24°C is approximately 1.494 MRayl. Using a reference liquid for relative measurement eliminates the need to directly measure the amplitude of the transmitted signal, thus eliminating the influence of sensor output fluctuations on the measurement results.

[0074] In this embodiment of the invention, the system further includes a temperature sensor and a temperature compensation module. The temperature sensor is used to detect the real-time temperature of the transformer oil under test, and the temperature compensation module is used to perform temperature correction on the sound velocity and / or acoustic impedance based on the real-time temperature. Preferably, the system integrates a Peltier element and a temperature sensor, and uses a closed-loop controller to strictly maintain the measured temperature at 24°C. As an alternative, a "temperature-acoustic parameter" compensation algorithm model can be established, and a software algorithm can be used to perform temperature correction on the sound velocity and impedance, thereby eliminating the need for a hardware temperature control module and making it suitable for low-cost portable devices. Through the cooperation of the temperature sensor and the temperature compensation module, software correction of temperature-acoustic parameters can be achieved, reducing the system's dependence on hardware constant temperature conditions and enhancing its adaptability to industrial environments.

[0075] In this embodiment of the invention, the operating frequency of the single ultrasonic sensor is 1MHz to 10MHz. Preferably, a single-crystal straight-probe ultrasonic sensor with a center frequency of 4MHz is selected, as this frequency can balance the penetration depth and resolution in oil. Depending on the oil layer thickness and the required penetration power, other frequency ultrasonic probes in the range of 1MHz to 10MHz can be used. Lower frequencies have stronger penetration but lower resolution, while higher frequencies have higher resolution but greater attenuation; both are within the protection scope of this invention.

[0076] In this embodiment of the invention, the single ultrasonic sensor can be replaced with an ultrasonic phased array probe or a multi-point matrix probe for simultaneously monitoring the water content distribution at different spatial locations. Expanding a single probe into an ultrasonic phased array or multi-point matrix probe allows for simultaneous monitoring of the water content distribution in different areas at the bottom of the fuel tank, achieving two-dimensional or three-dimensional humidity field monitoring in space, which has extremely high practical value in engineering diagnostics.

[0077] A second aspect of the present invention also provides a non-contact detection method for water content in transformer oil based on a single ultrasonic probe, comprising the following steps:

[0078] S1. A single ultrasonic sensor is placed on the outside of the first substrate, so that the ultrasonic pulse enters the transformer oil to be tested in the cavity through the first substrate, and is partially reflected and partially transmitted at the interface between the first substrate and the transformer oil to be tested, generating a first interface reflected echo.

[0079] S2. The transmitted wave propagates in the transformer oil under test to the interface between the second substrate and the transformer oil under test, where it is reflected to generate a second interface reflected echo.

[0080] S3. Receive the first interface reflected echo and the second interface reflected echo through the single ultrasonic sensor.

[0081] S4. Calculate the acoustic impedance of the transformer oil under test based on the reflected echo from the first interface;

[0082] S5. Calculate the sound velocity of the transformer oil under test based on the time difference between the reflected echo from the first interface and the reflected echo from the second interface.

[0083] S6. Calculate the density of the transformer oil to be tested based on the ratio of the acoustic impedance to the sound velocity;

[0084] S7. The water content of the transformer oil to be tested is inverted based on the mapping relationship between acoustic impedance, sound velocity, density and water content.

[0085] The technical solution of the present invention will be further described below through specific embodiments.

[0086] Example 1: Micro-water detection based on 5mm acrylic substrate.

[0087] In this embodiment, the measuring container has dimensions of 60mm in length, 140mm in width, and 10mm in height (oil layer thickness). The first substrate is a 5mm thick acrylic sheet, and the second substrate is also made of acrylic sheet. A single ultrasonic sensor, using a single-crystal straight probe with a center frequency of 4MHz, is positioned above the first substrate and coupled to it via a coupling agent.

[0088] First, substrate calibration was performed. The time of flight of the sound wave within the substrate was measured to be 3655.06 ns. Combined with the substrate thickness, the sound velocity on the substrate was calculated to be 2735.93 m / s. Based on the acrylic density of 1198 kg / m³, the acoustic impedance of the substrate was calculated. ≈3.277 MRayl (average is 3.24 MRayl).

[0089] Then, a reference measurement was performed. Pure water was injected into the first chamber as a reference liquid, and the intensity of the reflected echo signal at the interface between the first substrate and the pure water was measured. =23.67mV. The acoustic impedance of pure water at 24℃ is known. =1.494MRayl.

[0090] Furthermore, three transformer oil samples with different water contents—8 ppm, 23 ppm, and 33 ppm (calibrated using a Vaisala moisture analyzer)—were prepared and injected into the second chamber. Measurements were performed under a constant temperature of 24℃, and the reflected echo signal intensity (Vrms value) at the first interface of each sample was obtained: 27.468 mV for the 8 ppm sample, 27.81 mV for the 23 ppm sample, and 27.95 mV for the 33 ppm sample. Substituting these values ​​into the acoustic impedance calculation formula, the acoustic impedance was found to be 1.301 MRayl for the 8 ppm sample, 1.340 MRayl for the 23 ppm sample, and 1.349 MRayl for the 33 ppm sample. The results indicate that higher water content corresponds to higher acoustic impedance, showing a positive correlation.

[0091] Furthermore, the time of flight between the reflected echoes from the first and second interfaces of each sample was calculated using a cross-correlation algorithm: 14022.25 ns for the 8 ppm sample, 13863.94 ns for the 23 ppm sample, and 13798.64 ns for the 33 ppm sample. Substituting these values ​​into the sound velocity calculation formula, the sound velocity was obtained as follows: 1426.3 m / s for the 8 ppm sample, 1442.59 m / s for the 23 ppm sample, and 1449.42 m / s for the 33 ppm sample. The results indicate that the higher the water content, the faster the sound velocity. This is because the bulk modulus of water is much greater than that of oil, and the addition of trace amounts of water increases the equivalent bulk modulus of the mixture.

[0092] In summary, based on the fundamental acoustic relations Calculated density: The density of the 8 ppm sample was approximately 0.912 kg / dm³, the 23 ppm sample was approximately 0.929 kg / dm³, and the 33 ppm sample was approximately 0.930 kg / dm³. The results show that the density increases with increasing water content.

[0093] Example 2: Detection and comparison based on 3mm glass substrate.

[0094] In this embodiment, the first substrate was replaced with an optical-grade glass plate with a thickness of 3 mm, and the above measurement steps were repeated. The acoustic impedance of the 3 mm glass was measured to be approximately 11.475 MRayl (much higher than that of acrylic). Although the impedance matching between the glass and the oil was poor (extremely high reflectivity and low transmittance), the system was still able to capture the reflected echo from the second interface. The calculated acoustic impedance trend was consistent with that of the acrylic substrate: 1.309 MRayl for the 8 ppm sample, 1.339 MRayl for the 23 ppm sample, and 1.357 MRayl for the 33 ppm sample; the density calculation results were: 0.918 kg / dm³ for the 8 ppm sample, 0.928 kg / dm³ for the 23 ppm sample, and 0.936 kg / dm³ for the 33 ppm sample.

[0095] As a comparative experiment, when using ordinary glass with a thickness of 5mm as the first substrate, serious deviations were found in the calculated acoustic impedance and density data (for example, the impedance calculated for an 8ppm sample was only 1.228 MRayl, far below the theoretical value). Analysis revealed that the internal material of this batch of 5mm glass was non-uniform, causing aberrations and wavefront distortion in the ultrasonic beam during transmission, thus making the amplitude of the reflected echo no longer solely determined by the interface reflection coefficient. This comparative experiment further verified the limitations of the substrate material selection criteria in this invention—materials with good isotropy and high acoustic homogeneity must be used.

[0096] In summary, this invention, through a single ultrasonic probe and pulse-echo technology, combined with a three-layer dielectric model and relative measurement method, can simultaneously acquire three independent acoustic parameters of transformer oil—sound velocity, acoustic impedance, and density—under non-contact conditions, thereby achieving high-precision detection of water content. Key technologies employed, such as using a cross-correlation algorithm to accurately extract the time of flight, employing Vrms values ​​to characterize the reflected echo intensity, utilizing a dual-chamber structure for real-time calibration, and employing a temperature compensation module for temperature correction, collectively ensure the long-term stable operation and detection accuracy of this system in industrial environments.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A non-contact detection system for transformer oil water content using a single ultrasonic probe, characterized in that, include: A single ultrasonic sensor is used to emit ultrasonic pulses and receive echo signals. A first substrate is disposed between the single ultrasonic sensor and the transformer oil to be tested. The single ultrasonic sensor is disposed on the outside of the first substrate. It transmits ultrasonic pulses to the transformer oil to be tested through the first substrate and receives the first interface reflected echo from the interface between the first substrate and the transformer oil to be tested. A cavity for containing the transformer oil to be tested, one end of which is closed by the first substrate; The second substrate is disposed at the other end of the cavity and serves as an ultrasonic reflective surface to generate a second interface reflected echo between the transformer oil under test and the second substrate. The signal acquisition and processing unit is used to acquire the echo signal received by the single ultrasonic sensor, and calculate the acoustic impedance, sound velocity and density of the transformer oil under test based on the first interface reflected echo and the second interface reflected echo, and then invert the water content.

2. The non-contact detection system for transformer oil water content using a single ultrasonic probe as described in claim 1, characterized in that, The signal acquisition and processing unit includes: The acoustic impedance calculation module is used to calculate the acoustic impedance of the transformer oil under test based on the root mean square voltage value of the reflected echo from the first interface. The sound velocity calculation module is used to calculate the sound velocity of the transformer oil under test based on the time difference between the reflected echo from the first interface and the reflected echo from the second interface. The density calculation module is used to calculate the density of the transformer oil to be tested based on the ratio of the acoustic impedance to the sound velocity. The water content inversion module is used to invert the water content of the transformer oil under test based on the mapping relationship between acoustic impedance, sound velocity, density and water content.

3. The non-contact detection system for transformer oil water content using a single ultrasonic probe as described in claim 2, characterized in that, The acoustic impedance calculation module uses a relative measurement method to calculate the acoustic impedance of the transformer oil under test. ； The intermediate variable K is: ； In the formula, The acoustic impedance of the transformer oil to be tested. Let be the acoustic impedance of the first substrate. As a reference liquid, The strength of the transformer oil to be tested. The reflected echo signal intensity of the ultrasonic wave at the interface between the first substrate and the reference liquid is represented by the root mean square voltage value.

4. The non-contact detection system for transformer oil water content using a single ultrasonic probe as described in claim 1, characterized in that, The sound velocity calculation module uses a cross-correlation algorithm to calculate the time difference between the echo reflected from the first interface and the echo reflected from the second interface: ; In the formula, The signal reflected from the first interface. The signal reflected from the second interface. For time-delay variables, find the cross-correlation function. The peak position determines the time difference, and the speed of sound is calculated according to the following formula: ; The velocity of sound in the transformer oil to be tested. The thickness of the transformer oil to be measured in the cavity. The time difference is mentioned.

5. The non-contact detection system for transformer oil water content using a single ultrasonic probe as described in claim 1, characterized in that, The cavity includes a first chamber and a second chamber arranged side by side. The first chamber is used to contain a reference liquid, and the second chamber is used to contain the transformer oil to be tested. The single ultrasonic sensor performs measurements sequentially above the first chamber and the second chamber to achieve real-time calibration of the reference signal and the target signal.

6. The non-contact detection system for transformer oil water content using a single ultrasonic probe as described in claim 1, characterized in that, The reference liquid can be any one of pure water, ethanol, or standard silicone oil, or a solid block with known acoustic impedance can be used as a calibration reference.

7. The non-contact detection system for transformer oil water content using a single ultrasonic probe as described in claim 1, characterized in that, The material of the first substrate is a material with uniform acoustic impedance and isotropic, selected from any one of acrylic, glass, polycarbonate, polyetheretherketone, epoxy resin, quartz glass or ceramic.

8. The non-contact detection system for transformer oil water content using a single ultrasonic probe as described in claim 1, characterized in that, It also includes a temperature sensor and a temperature compensation module. The temperature sensor is used to detect the real-time temperature of the transformer oil under test, and the temperature compensation module is used to perform temperature correction on the sound velocity and / or acoustic impedance based on the real-time temperature.

9. The non-contact detection system for transformer oil water content using a single ultrasonic probe as described in claim 1, characterized in that, The single ultrasonic sensor is replaced by an ultrasonic phased array probe or a multi-point matrix probe to simultaneously monitor the water content distribution at different spatial locations.

10. A non-contact method for detecting water content in transformer oil based on a single ultrasonic probe, characterized in that, Includes the following steps: S1. A single ultrasonic sensor is placed on the outside of the first substrate, so that the ultrasonic pulse enters the transformer oil to be tested in the cavity through the first substrate, and is partially reflected and partially transmitted at the interface between the first substrate and the transformer oil to be tested, generating a first interface reflected echo. S2. The transmitted wave propagates in the transformer oil under test to the interface between the second substrate and the transformer oil under test, where it is reflected to generate a second interface reflected echo. S3. Receive the first interface reflected echo and the second interface reflected echo through the single ultrasonic sensor. S4. Calculate the acoustic impedance of the transformer oil under test based on the reflected echo from the first interface; S5. Calculate the sound velocity of the transformer oil under test based on the time difference between the reflected echo from the first interface and the reflected echo from the second interface. S6. Calculate the density of the transformer oil to be tested based on the ratio of the acoustic impedance to the sound velocity; S7. The water content of the transformer oil to be tested is inverted based on the mapping relationship between acoustic impedance, sound velocity, density and water content.

Images