Broadband ultrasonic device capable of being used for detecting micro water in transformer oil

Abstract

The invention discloses a broadband ultrasonic device capable of being used for detecting micro water in transformer oil, an ultrasonic transmitting module comprises a transmitting control unit, a transmitting driving unit and a transducer, and the ultrasonic transmitting module transmits a multi-frequency ultrasonic signal; the ultrasonic receiving module comprises an ultrasonic receiving unit, a receiving frequency control unit, a signal processing unit, an ultrasonic A / D conversion unit and an output interface. The ultrasonic receiving module receives and processes ultrasonic signals and then transmits the ultrasonic signals to the upper computer. The ultrasonic transmitting modules are arranged on one side of the transformer insulating oil tank in an array mode, the ultrasonic receiving modules are arranged on the other side of the transformer insulating oil tank in an array mode, and the ultrasonic transmitting modules and the ultrasonic receiving modules are oppositely arranged. According to the invention, on-line detection of the transformer insulating oil can be realized.

Description

Technical Field

[0001] The invention relates to a broadband ultrasonic device used in the field of transformer insulating oil detection and can be used for detecting micro-water in transformer oil. Background Art

[0002] At present, the main means of monitoring the operation safety of power transformers in my country is to perform regular power outage maintenance and overhaul of transformers. The "Guidelines for the Maintenance of Power Transformers" stipulates that newly commissioned transformers must undergo minor repairs every year. Except for the first major overhaul five years after commissioning, the remaining major overhauls can be spaced at most 10 years apart. Although the regular maintenance strategy has played a certain effective role in the safe and stable operation of my country's power equipment for a long time, with the continuous acceleration of the pace of social development, the continuous expansion of the scale of the power grid, and the continuous updating of power components, the disadvantages of traditional maintenance strategies have become increasingly prominent. According to the provisions in the maintenance manual, normally operating transformers must be withdrawn from operation and maintained on schedule, which will increase the frequency of transformer outages, increase the maintenance workload, increase the maintenance cost, and cause the problem of "excessive maintenance". In addition, if an abnormality occurs during the normal operation of the transformer, it may not be repaired in time, resulting in a decrease in the operation of the equipment, bringing many hidden dangers to the operation of the power grid and causing the phenomenon of "insufficient maintenance" of the equipment. The disadvantages of traditional maintenance methods are becoming increasingly prominent, and a reasonable operating condition maintenance mechanism has become the inevitable development direction of the power industry at home and abroad.

[0003] Maintaining a good insulation state is the key to a large power transformer having a good operating condition. At present, all power transformers in the power industry at home and abroad use transformer insulating oil as the main material for insulation and cooling. The aging of the transformer, the deterioration of the insulation performance, and the decomposition of its internal insulating materials will affect the change of the water content in the transformer oil. With the increase of the water content in the oil, the insulation performance of the transformer will decrease. When it reaches a certain level, the transformer may even have major faults such as burning of the insulating material and breakdown accidents, and this is an irreversible process. Therefore, real-time monitoring of the water content in the transformer oil is of great significance to ensure the safe operation of the transformer. Transformer oil is a liquid insulating medium. If the water content in the oil is too high, it will cause a series of faults that need to be solved in the transformer operation, such as increasing the loss of the insulating medium and reducing the breakdown voltage. When the power transformer is working normally, a strong magnetic field will be generated. If the water content in the transformer oil exceeds the standard when the transformer is working, under its complex strong magnetic field, the water and oil will be arranged in polarity order and arranged into impurity "bridges" in the direction of the electric field, so that the leakage current flowing through the impurity bridge increases and the breakdown voltage of the oil is reduced.

[0004] At present, the detection methods of trace water content in power transformer insulating oil are mainly divided into two categories. One is offline detection, including: Karl Fischer titration (coulometric method), distillation method, chromatography, resonant cavity perturbation method, etc. The other is online detection method, including: dielectric constant method, radio frequency method and infrared method, etc. Compared with the online detection method of trace water content in transformer oil, the detection accuracy of its offline detection method is higher. Both the international standard ICE 60296 and the domestic standard GB / T 7600-2014 use Karl Fischer titration as the standard detection method for detecting trace water content in transformer oil in the power industry. At present, there is a lack of stable, reliable, convenient and efficient methods for online detection of transformer oil. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a broadband ultrasonic device that can be used for detecting trace water in transformer oil, thereby enabling online detection of transformer insulating oil.

[0006] A technical solution to achieve the above object is: a broadband ultrasonic device that can be used for detecting trace water in transformer oil, including an ultrasonic transmitting module and an ultrasonic receiving module;

[0007] The ultrasonic transmitting module includes a transmitting control unit, a transmitting driving unit and a transducer. The transmitting control unit provides a signal to generate a carrier pulse signal, which is transmitted to the transmitting driving unit. The transmitting driving unit performs a voltage boost process on the received pulse signal, outputs a high-power signal, and drives the transducer to transmit a multi-frequency ultrasonic signal.

[0008] The ultrasonic receiving module includes an ultrasonic receiving unit, a receiving frequency control unit, a signal processing unit, an ultrasonic A / D conversion unit and an output interface; the ultrasonic receiving unit receives an ultrasonic signal and inputs it into the receiving frequency control unit, the receiving frequency control unit matches the receiving signal with the working frequency of the signal processing unit, the signal processing unit performs signal processing, and then the ultrasonic A / D conversion unit converts it into a digital signal, which is transmitted to the host computer through the output interface;

[0009] The ultrasonic transmitting module is arranged in an array on one side of the transformer insulating oil tank, and the ultrasonic receiving module is arranged in an array on the other side. The ultrasonic transmitting module and the ultrasonic receiving module are arranged opposite to each other.

[0010] Furthermore, the transmission control unit of the ultrasonic transmission module includes a frequency control unit and a power control unit. The frequency control unit determines the carrier frequency, and the power control unit adjusts the width and amplitude of the pulse.

[0011] Furthermore, the frequency, width and amplitude of the ultrasonic signals emitted by different ultrasonic emission modules are different.

[0012] Furthermore, the frequencies of the ultrasonic waves emitted by the ultrasonic emission module are 200kHz, 300kHz, 400kHz and 500kHz.

[0013] Furthermore, the signal processing unit of the ultrasonic receiving module includes a detector and a bandpass filter unit. The detector detects and extracts effective information of the signal, removes useless components, and then inputs the information into the bandpass filter unit. The bandpass filter unit filters out unnecessary high-frequency and low-frequency signals and only retains effective signals within a specific frequency range.

[0014] Furthermore, the output interface is a RS232 interface.

[0015] Furthermore, the transformer insulating oil tank is a rectangular parallelepiped, and the two side surfaces are respectively an incident surface and a receiving surface. The ultrasonic transmitting module is arranged on the incident surface, and the ultrasonic receiving module is arranged on the receiving surface.

[0016] Furthermore, the bottom width of the transformer insulating oil tank is 500mm-1000mm.

[0017] Furthermore, the ultrasonic transmitting module and the ultrasonic receiving module are connected to the host computer through leads respectively, and the host computer records the ultrasonic transmitting signal and the receiving signal respectively. The host computer inputs the calculation results into the neural network for training, and after the training is completed, the micro-water content in the transformer oil insulating oil is detected through ultrasonic signals.

[0018] Furthermore, the host computer calculates based on the ultrasonic transmission signal and the received signal to obtain the attenuation coefficient, amplitude, phase, flight time and flight speed of ultrasonic waves of different frequencies passing through transformer oils with different water contents.

[0019] The broadband ultrasonic device for detecting trace water in transformer oil of the present invention has the following advantages and effects:

[0020] (1) Compared with the existing technology, the use of ultrasonic technology can truly achieve zero impact on the material being tested, making the online detection data more accurate and conducive to the training of subsequent prediction models.

[0021] (2) Using ultrasonic waves of different frequencies to comprehensively detect the water content of the substance being tested has higher accuracy than using a single frequency.

[0022] (3) The model is trained using broadband ultrasound data of amplitude and phase plus attenuation coefficient, flight time, and velocity. This is more representative than the data of amplitude and phase or attenuation coefficient, flight time, and velocity used only in the literature and prior art, thereby improving the accuracy of detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1It is a structural schematic diagram of a broadband ultrasonic device that can be used for detecting trace water in transformer oil according to the present invention;

[0024] Figure 2 It is a schematic diagram of the structure of the ultrasonic transmitting module of the present invention;

[0025] Figure 3 It is a schematic structural diagram of an ultrasonic receiving module of the present invention;

[0026] Figure 4 Schematic diagram of ultrasonic attenuation in transformer oil. DETAILED DESCRIPTION

[0027] In order to better understand the technical solution of the present invention, the following is a detailed description through specific embodiments:

[0028] See also Figure 1 The invention discloses a broadband ultrasonic device for detecting micro-water in transformer oil, wherein a group of four ultrasonic transmitting modules 2 and a group of four ultrasonic receiving modules 3 are respectively arranged on both sides of the transformer insulating oil tank 1. The four ultrasonic receiving modules receive the waveform emitted on the other side of the oil, and display the received waveform on the computer through a digital signal processing circuit. The relationship between waveforms of different frequencies and water content is established by analyzing the relationship, so as to facilitate subsequent data analysis.

[0029] The transformer insulating oil tank is a rectangular parallelepiped, with two sides respectively being the incident surface and the receiving surface. The ultrasonic transmitting module is arranged on the incident surface, and the ultrasonic receiving module is arranged on the receiving surface. In order to ensure that the ultrasonic wave can reflect the micro-water content of the oil when passing through the oil, the ultrasonic wave is required to pass through a minimum stroke; at the same time, in order to ensure that the attenuation of the ultrasonic wave meets the detection requirements, the maximum stroke needs to be limited. Therefore, the bottom width of the transformer insulating oil tank is required to be 500mm-1000mm.

[0030] See also Figure 2 . The ultrasonic transmitting module includes a transmitting control unit 20, a transmitting driving unit 23 and a transducer 24. The transmitting control unit includes a frequency control unit 21 and a power control unit 22. The frequency control unit 21 determines the carrier frequency. The power control unit 22 selects a suitable power signal to adjust the pulse width and amplitude according to the type and capacity of the transformer. The transmitting control unit 20 generates the carrier pulse signal required by the transducer according to the provided signal. The carrier pulse signal is transmitted to the transmitting driving unit 23. The transmitting driving unit 23 performs a voltage boost processing on the received pulse signal, outputs a high-power signal, and drives the transducer 24 to transmit a multi-frequency ultrasonic signal. The four ultrasonic transmitting modules emit frequencies of 200kHz, 300kHz, 400kHz, and 500kHz respectively.

[0031] See also Figure 3. The ultrasonic receiving module 3 includes an ultrasonic receiving unit 31, a receiving frequency control unit 32, a signal processing unit 33, an ultrasonic A / D conversion unit 34 and an output interface 35. The ultrasonic receiving unit 31 receives the ultrasonic signal and inputs it into the receiving frequency control unit 32. The receiving frequency control unit 32 adjusts the frequency of the signal according to the requirements of the system so that the signal can match the working frequency of the subsequent processing unit. This step is crucial for the effective transmission and accurate processing of the signal to ensure that the signal will not be distorted or interfered. The frequency-adjusted signal enters the signal processing unit 33. The signal processing unit 33 includes a detector 331 and a bandpass filter unit 332. The detector 331 detects and extracts the effective information of the signal and removes useless components. The detector can identify the waveform characteristics in the signal to ensure the stability of the signal. The signal is then input into the bandpass filter unit 332, which filters out unnecessary high-frequency and low-frequency signals and retains only the effective signals within a specific frequency range. This step can effectively reduce noise and interference to ensure that the most accurate signal is received. Next, the filtered signal enters the ultrasonic A / D conversion unit 34, during which the analog signal is converted into a digital signal. A / D (analog / digital) conversion is the core link in the digital signal processing system, which converts the analog signal of the ultrasound into a digital format so that it can be processed by a computer or other digital device. Finally, the digital signal is transmitted to the host computer 4 via the RS232 interface. RS232 is a widely used serial communication interface that is responsible for stably and accurately transmitting the converted digital signal to the host computer, so that the host computer can perform further data analysis, processing or storage.

[0032] The ultrasonic transmitting module and the ultrasonic receiving module are connected to the host computer 4 through leads respectively. The host computer 4 records the ultrasonic transmitting signal and the receiving signal respectively. The host computer inputs the calculation results into the neural network 5 for training, and after the training is completed, the micro-water content in the transformer oil insulating oil is detected by ultrasonic signals.

[0033] Ultrasonic detection technology mainly uses the propagation characteristics of ultrasonic waves in the medium, such as the energy loss of ultrasonic waves when propagating in the medium, and the reflection, refraction and scattering when propagating to the interface between two media. Ultrasonic industrial measurement mainly uses the relationship between ultrasonic sound velocity, acoustic attenuation, acoustic impedance and other acoustic parameters of ultrasonic waves and industrial process parameters such as viscosity, density, temperature, particle size and number to describe the propagation characteristics of ultrasonic waves in the medium, thereby realizing the measurement of industrial process parameters by ultrasonic waves.

[0034] The total attenuation coefficient of ultrasound is:

[0035] α 总 =α s +α η +α ξ (1)

[0036] In the formula, α s is the scattering attenuation coefficient, α η is the viscous attenuation coefficient, α ξ is the thermal conduction attenuation coefficient, where thermal conduction and viscous attenuation both belong to absorption attenuation. The schematic diagram of ultrasonic attenuation in transformer oil is shown in Figure 4 As shown:

[0037] (1) Scattering attenuation formula:

[0038]

[0039] Where: r is the radius of the scattering particle; f is the ultrasonic frequency; c is the ultrasonic propagation speed.

[0040] (2) Viscous attenuation formula:

[0041]

[0042] Where: ρ is the density of the liquid medium; η is the viscosity coefficient.

[0043] (3) Heat conduction attenuation formula:

[0044]

[0045] Where: χ is the thermal conductivity; c V and c P are the constant volume specific heat and constant pressure specific heat of the medium respectively. V =c P / k0, k0 is the constant heat ratio of the medium.

[0046] In actual measurement, it is difficult to measure the magnitude of each attenuation separately, so the total attenuation is usually measured. The total attenuation coefficient is:

[0047]

[0048] Where: α 总 The unit is dB / cm, p is the sound pressure amplitude of the ultrasonic echo, and p0 is the sound pressure amplitude at the ultrasonic sound source. The sound pressure amplitude of the ultrasonic echo can be obtained by receiving the voltage amplitude output by the probe. The sound pressure amplitude at the ultrasonic sound source cannot be directly measured. In this study, the sound pressure amplitude of distilled water at room temperature (25°C) at a distance L from the sound source is used as the reference value to measure the relative change in ultrasonic attenuation. In this way, the attenuation coefficient can be obtained as follows:

[0049]

[0050] After calculating the attenuation coefficients of different frequencies, the amplitudes and phases of different frequencies are calculated and used as input parameters for subsequent data analysis. Since the ultrasonic signal is set as a sine wave, the calculation formulas for the amplitude and phase are as follows:

[0051] The ultrasonic signal is as shown in formula (7)

[0052] x(t)=Asin(ωt+φ) (7)

[0053] The signal satisfies the Dirichlet condition and can be expressed as:

[0054] x(t)=C0sin(ωt)+C1cos(ωt) (8)

[0055] x(t)=Acos(φ)sin(ωt)+Asin(φ)cos(ωt) (9)

[0056] Combining equations (8)-(9) we can get (10):

[0057] C0=Acos(φ),C1=Asin(φ) (10)

[0058] Therefore, the expressions of amplitude and phase are respectively:

[0059]

[0060] In equations (11) and (12), A is the amplitude; C0 and C1 are two constants.

[0061] The broadband ultrasonic detection of this device is designed to provide comprehensive and accurate ultrasonic data, and use formulas to calculate the attenuation coefficient, amplitude, phase, and flight time and speed (which can be calculated in the ultrasonic control module) of different frequencies passing through transformer oil with different water contents, so as to facilitate subsequent training using neural networks.

[0062] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A broadband ultrasonic device for detecting trace water in transformer oil, comprising an ultrasonic transmitting module and an ultrasonic receiving module, characterized in that: The ultrasonic transmitting module includes a transmitting control unit, a transmitting driving unit and a transducer. The transmitting control unit provides a signal to generate a carrier pulse signal, which is transmitted to the transmitting driving unit. The transmitting driving unit performs a voltage boost process on the received pulse signal, outputs a high-power signal, and drives the transducer to transmit a multi-frequency ultrasonic signal. The ultrasonic receiving module includes an ultrasonic receiving unit, a receiving frequency control unit, a signal processing unit, an ultrasonic A / D conversion unit and an output interface; the ultrasonic receiving unit receives an ultrasonic signal and inputs it into the receiving frequency control unit, the receiving frequency control unit matches the receiving signal with the working frequency of the signal processing unit, the signal processing unit performs signal processing, and then the ultrasonic A / D conversion unit converts it into a digital signal, which is transmitted to the host computer through the output interface; The ultrasonic transmitting module is arranged in an array on one side of the transformer insulating oil tank, and the ultrasonic receiving module is arranged in an array on the other side. The ultrasonic transmitting module and the ultrasonic receiving module are arranged opposite to each other.

2. A broadband ultrasonic device for detecting trace water in transformer oil according to claim 1, characterized in that: The transmission control unit of the ultrasonic transmission module includes a frequency control unit and a power control unit. The frequency control unit determines the carrier frequency, and the power control unit adjusts the width and amplitude of the pulse.

3. A broadband ultrasonic device for detecting trace water in transformer oil according to claim 2, characterized in that: The frequency, width and amplitude of the ultrasonic signals emitted by different ultrasonic transmitting modules are different.

4. A broadband ultrasonic device for detecting trace water in transformer oil according to claim 3, characterized in that: The frequencies of the ultrasonic waves emitted by the ultrasonic emission module are 200kHz, 300kHz, 400kHz and 500kHz.

5. A broadband ultrasonic device for detecting trace water in transformer oil according to claim 1, characterized in that: The signal processing unit of the ultrasonic receiving module includes a detector and a bandpass filter unit. The detector detects and extracts effective information of the signal, removes useless components, and then inputs the information into the bandpass filter unit. The bandpass filter unit filters out unnecessary high-frequency and low-frequency signals and only retains effective signals within a specific frequency range.

6. A broadband ultrasonic device for detecting trace water in transformer oil according to claim 1, characterized in that: The output interface is a RS232 interface.

7. A broadband ultrasonic device for detecting trace water in transformer oil according to claim 1, characterized in that: The transformer insulating oil tank is a rectangular parallelepiped, and the two side surfaces are respectively an incident surface and a receiving surface. The ultrasonic transmitting module is arranged on the incident surface, and the ultrasonic receiving module is arranged on the receiving surface.

8. A broadband ultrasonic device for detecting trace water in transformer oil according to claim 7, characterized in that: The bottom width of the transformer insulating oil tank is 500mm-1000mm.

9. A broadband ultrasonic device for detecting trace water in transformer oil according to claim 1, characterized in that: The ultrasonic transmitting module and the ultrasonic receiving module are connected to the host computer through leads respectively. The host computer records the ultrasonic transmitting signal and the receiving signal respectively. The host computer inputs the calculation results into the neural network for training, and after the training is completed, the micro-water content in the transformer oil insulating oil is detected through ultrasonic signals.

10. A broadband ultrasonic device for detecting trace water in transformer oil according to claim 9, characterized in that: The host computer calculates based on the ultrasonic transmission signal and the received signal to obtain the attenuation coefficient, amplitude, phase, flight time and flight speed of ultrasonic waves of different frequencies passing through transformer oils with different water contents.

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