A method and apparatus for non-contact in-oil dissolved gas monitoring

Abstract

This invention belongs to the field of oil gas detection technology and discloses a non-contact in-situ monitoring method and device for dissolved gases in oil. The in-situ monitoring method includes the following steps: selecting the emission laser wavelength of the excitation light source based on the absorption spectrum of the target gas dissolved in the oil, according to the type of the target gas; filling the oil sample cell (transparent at both ends) with the protective oil for the power equipment to be tested; then, incident the modulated collimated laser into the oil sample cell, and the beam emitted from the oil sample cell irradiates the surface of a tuning fork. The vibration signal of the tuning fork, based on the photothermoelastic effect and resonance enhancement effect, can reflect the change in light intensity caused by the absorption of dissolved gases in the protective oil for the power equipment; by demodulating the vibration signal of the tuning fork and extracting the harmonic signal amplitude, the concentration information of the gas contained in the protective oil for the power equipment to be tested can be obtained. This invention can directly detect the concentration of dissolved gases in oil in situ without degassing and without the detection unit contacting the oil sample.

Description

Technical Field

[0001] This invention belongs to the field of oil gas detection technology, and more specifically, relates to a non-contact in-situ monitoring method and device for dissolved gases in oil. Background Technology

[0002] Transformers, converter transformers, high-voltage shunt reactors, and other oil-filled electrical equipment (hereinafter referred to as "equipment") are the heart of the power grid. Their safe operation is of great significance to ensuring power supply and grid security, and is related to national energy security and the lifeline of the national economy. With the construction of new power systems, the proportion of high-voltage, large-capacity oil-filled electrical equipment is increasing, making it a top priority for power supply. However, equipment failures and even explosions caused by internal overheating and discharge pose a great threat to the safe and stable operation of the power grid. Therefore, continuous monitoring and early warning of the internal operating status of the equipment are essential. Currently, the most effective method is to judge this by the absolute content and relative increase of characteristic gases dissolved in the insulating oil.

[0003] Most current oil gas detection technologies require oil-gas separation units to degas dissolved gases in the oil. This process is not only very time-consuming and unable to provide timely warnings of equipment failures, but its performance is also limited by the gas content of the insulating oil. For example, when the gas content of the insulating oil is low, the content of characteristic gases extracted by the oil-gas separation unit is low, and the response signal of some monitoring devices does not meet the requirements, resulting in low reliability of monitoring data. Conversely, when the gas content of the insulating oil is high, especially when equipment discharge causes a sudden increase in gas and oil-gas mixing, the degassing unit of some monitoring devices cannot function properly and cannot reflect the equipment status in a timely manner. Degassing units are generally divided into two types according to their working principle: vacuum degassing and dynamic headspace degassing. When using dynamic headspace degassing, the insulating oil inevitably introduces outside air, leading to an increase in the gas content of the returned oil and affecting equipment safety. When using vacuum degassing, especially with piston pumps and diaphragm pumps, the pump's frequent reciprocating motion often leads to poor sealing, causing the device to malfunction or even leak oil, affecting equipment safety. Although photothermal spectroscopy based on hollow optical fibers has been applied to in-situ detection of dissolved gases in oil, the core of the hollow optical fiber is very thin (on the micrometer scale), which causes the oil to diffuse into the core for a considerable period of time (more than 1 hour). Therefore, this method is also difficult to monitor and warn of equipment failures in a timely manner.

[0004] With increasing emphasis on environmental protection, numerous reports have emerged regarding airborne gas composition detection technologies in the field of atmospheric environmental monitoring. Taking the commonly used photoacoustic spectroscopy as an example, its basic principle is that after a modulated laser irradiates the gas to be tested, the gas absorbs and releases laser energy, causing changes in its temperature field. These changes in the temperature field within the cavity, in turn, cause changes in the sound field. High-sensitivity microphones or quartz tuning forks can capture these changes and thus deduce the concentration information of the gas to be tested. However, when photoacoustic spectroscopy is applied to in-situ monitoring of dissolved gases in oil, the microphone inevitably comes into contact with the oil. This leads to a sharp deterioration in the microphone's sensitivity, and long-term stability is difficult to guarantee.

[0005] Therefore, there is an urgent need for a non-contact in-situ monitoring method and device for dissolved gases in oil that can prevent degassing. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the prior art, the purpose of the present invention is to provide a non-contact in-situ monitoring method and device for dissolved gas in oil, which can directly detect the concentration of dissolved gas in oil in situ without degassing and without the detection unit contacting the oil sample.

[0007] To achieve the above objectives, according to one aspect of the present invention, a non-contact in-situ monitoring method for dissolved gases in oil is provided, comprising the following steps: selecting the emission wavelength of an excitation light source based on the absorption spectrum of the target gas dissolved in the oil, wherein the absorption spectrum is red-shifted and broadened compared to that in the gas phase; filling a two-sided transparent oil sample cell with the protective oil for the power equipment to be tested; then, incident a modulated collimated laser from the transparent end of the oil sample cell into the oil sample cell, and irradiating the surface of a tuning fork with the beam emitted from the other transparent end of the oil sample cell; wherein the vibration signal of the tuning fork, based on the photothermoelastic effect and resonance enhancement effect, can reflect the change in light intensity caused by the absorption of dissolved gases in the protective oil for the power equipment; and obtaining the concentration information of the gas contained in the protective oil for the power equipment to be tested by extracting the harmonic signal amplitude through demodulation of the vibration signal of the tuning fork.

[0008] As a further preferred embodiment of the present invention, the light beam emitted from the oil sample pool specifically illuminates the middle of the root of the two arms of the tuning fork.

[0009] As a further preferred embodiment of the present invention, the modulation frequency of the modulated collimated laser corresponds to the resonance frequency of the tuning fork.

[0010] As a further preferred embodiment of the present invention, the tuning fork is a tuning fork made of piezoelectric material, or a tuning fork made of non-piezoelectric material;

[0011] When the tuning fork is made of piezoelectric material, the demodulation is performed using electrical demodulation or optical demodulation.

[0012] When the tuning fork is made of a non-piezoelectric material, the demodulation is performed using an optical demodulation method.

[0013] As a further preferred embodiment of the present invention, the environment in which the tuning fork is located is a normal pressure air environment or a low pressure air environment;

[0014] When the tuning fork is in a low-pressure air environment, it is placed in a pressure vessel with a high-transmittance window, and the light beam emitted from the oil sample cell irradiates the surface of the tuning fork through the high-transmittance window; the transmittance of the high-transmittance window at the corresponding wavelength of the laser is not less than 90%.

[0015] As a further preferred embodiment of the present invention, the oil sample pool is provided with an oil inlet and an oil outlet, which are used for oil inlet and oil outlet respectively;

[0016] The protective oil for the electrical equipment under test, which fills the oil sample pool, is either in a static state or in a flow state that flows at a preset flow rate.

[0017] Preferably, the protective oil of the power equipment under test is the transformer oil under test.

[0018] According to another aspect of the present invention, the present invention provides a non-contact in-situ monitoring device for dissolved gases in oil, used to perform the above-described non-contact in-situ monitoring method for dissolved gases in oil. The device includes an excitation light source, a signal demodulation and processing system, and a collimator, an oil sample cell, a focusing lens, and a tuning fork arranged sequentially along the optical path of the excitation light source; wherein...

[0019] The oil sample pool is used to fill the protective oil of the electrical equipment to be tested.

[0020] The laser beam emitted from the excitation light source is modulated and then incident on the collimator to obtain a modulated collimated laser. The wavelength of the laser beam is selected based on the type of target gas and the absorption spectrum of the target gas dissolved in the oil. The absorption spectrum is red-shifted and broadened compared to that in the gas phase.

[0021] The focusing lens is used to converge the light beam emitted from the oil sample pool onto the surface of the tuning fork;

[0022] The signal demodulation and processing system is used to demodulate the vibration signal of the tuning fork, extract the harmonic signal amplitude, and thus invert the concentration information of the gas contained in the protective oil of the power equipment under test.

[0023] As a further preferred embodiment of the present invention, the modulation is performed by generating a modulation signal through a signal generator and applying it to the excitation light source, or by modulating the laser beam emitted from the excitation light source through a chopper.

[0024] Compared with the prior art, the present invention, through the above-described technical solution, is the first to apply the photothermal elastic technology for detecting gas concentration in air to the detection of dissolved gases in oil, thus avoiding the degassing process required for the detection of gases in oil. Since no degassing process is required, the present invention can avoid the limitations of degassing process such as gas content and the operating conditions of degassing devices.

[0025] For power equipment (especially high-voltage substation equipment such as transformers and high-voltage shunt reactors), the protective oil plays a crucial role in equipment safety (transformers have the highest safety requirements). This invention, based on photothermoelastic technology, achieves non-contact in-situ monitoring of dissolved gases in oil, significantly different from existing technologies that mostly employ degassing detection methods. Unlike the photothermoelastic effect in gases, dissolved gases in oil exhibit reduced electron cloud density and intermolecular distance due to the principle of "like dissolves like," resulting in weakened stretching vibrations and a redshifted, broadened absorption spectrum compared to the gas phase. Furthermore, the tuning fork detection unit designed in this invention operates outside the oil sample pool, employing a non-contact method, thus avoiding the challenge of the detection unit operating in an oil environment. This invention overcomes the problems of gas absorption spectrum changes and the inability of the detection unit to operate in an oil environment.

[0026] This invention enables non-contact in-situ monitoring of dissolved gases in the protective oil of power equipment without degassing, and has the following four significant advantages: (1) No oil-gas separation device is required, reducing the complexity of the system; (2) The response time is greatly shortened, enabling rapid and timely fault warning; (3) Many uncertainties introduced by oil-gas separation are eliminated, greatly reducing the false alarm rate and missed alarm rate of the system; (4) The tuning fork detector does not contact the oil sample, avoiding the influence of oil on the performance of the tuning fork and also avoiding the contamination of the oil by the tuning fork material. Attached Figure Description

[0027] Figure 1 This is a flowchart of the non-contact in-situ monitoring method for dissolved gases in oil according to the present invention.

[0028] Figure 2 This is a schematic diagram of the non-contact in-situ monitoring device for dissolved gases in oil according to the present invention.

[0029] Figure 2 The meanings of the labels in the attached figures are as follows: 1 is the modulation module, 2 is the excitation light source, 3 is the collimator, 4 is the oil sample cell (transparent at both ends), 5 is the focusing lens, 6 is the tuning fork, and 7 is the signal demodulation and processing system. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] In summary, the non-contact in-situ monitoring method for dissolved gases in oil of this invention involves modulating an excitation light beam, which is then collimated and incident into an oil sample cell. After absorption by the dissolved gases in the oil, the beam exits the oil sample cell (the excitation light source is used to excite the dissolved gases in the oil to absorb the light; when the laser is incident into the oil sample cell, the dissolved gases absorb the light energy, causing a change in the intensity of the emitted light). Finally, the light is focused onto the surface of a tuning fork (it can be at any position, but the effect is best when it is incident on the middle of the roots of the two arms of the Y-shaped tuning fork). The concentration information of the gas is then deduced by demodulating the vibration signal of the tuning fork and extracting its harmonic signal amplitude. The corresponding device may include an excitation light source, a collimator, an oil sample cell, a tuning fork, and a signal demodulation and processing system (a separate modulation module may be optionally provided for modulating the excitation laser).

[0032] Taking transformer oil No. 25, which is the national standard for 750kV transformers, as an example:

[0033] Example 1

[0034] like Figure 1 As shown, this invention provides a non-contact in-situ monitoring method for dissolved gases in oil. An example of its use for detecting dissolved acetylene in oil is as follows: It includes an excitation light source 2, a collimator 3, an oil sample cell 4, and a tuning fork 6. The oil sample cell 4 is filled with transformer oil containing dissolved gas to be measured. The excitation light source 2 is used to excite the dissolved acetylene in the oil to absorb the gas. The collimator 3 is used to collimate the light beam emitted from the excitation light source and direct it into the oil sample cell. The tuning fork 6 detects the change in light intensity caused by the absorption of dissolved acetylene based on the photothermoelastic effect and resonance enhancement effect. The in-situ monitoring method includes:

[0035] S1. After the excitation light is modulated, the beam is collimated and incident into the oil sample cell. The dissolved gas in the oil absorbs the light energy, causing a change in the intensity of the emitted light.

[0036] S2. The light beam emitted from the oil sample cell shines on the surface of the tuning fork and is detected by the tuning fork;

[0037] S3. The concentration information of the gas is inverted by demodulating the vibration signal of the tuning fork and extracting its harmonic signal amplitude.

[0038] Specifically, in S1, the excitation source 2 is selected based on the absorption spectrum of acetylene dissolved in oil. Due to the principle of "like dissolves like," the electron cloud density of acetylene dissolved in oil decreases, and the intermolecular distance also decreases, resulting in a weakening of stretching vibrations. Consequently, the absorption spectrum is red-shifted and broadened compared to the gas phase. In this example, the excitation source 2 is a DFB laser with a wavelength of 1532.8 nm, corresponding to the peak wavelength of the absorption spectrum of acetylene dissolved in oil.

[0039] Specifically, in S1, the excitation light source 2 can be modulated by generating a modulation signal through a signal generator and loading it onto the laser, or it can be modulated by an external method such as a chopper. In this example, a 32.768kHz sine wave is generated by a signal generator to modulate the driving current, with a peak-to-peak value of 600mV. The basic operating current of the laser is 200mA, and the operating temperature is 34 degrees Celsius.

[0040] Specifically, in S1, in order to ensure the consistency of the subsequent experimental environment and to calibrate the measurement signal, it is necessary to control the excitation light power. The output light power at the back end of the collimator is 60mW.

[0041] Specifically, in S1, the modulation frequency of the excitation light source 2 corresponds to the resonance frequency of the tuning fork 6.

[0042] Specifically, in S2, the tuning fork 6 can be made of piezoelectric material or non-piezoelectric material.

[0043] If the tuning fork 6 is made of piezoelectric material, then the demodulation method described in S3 is either electrical demodulation or optical demodulation.

[0044] If the tuning fork 6 is made of a non-piezoelectric material, then the demodulation method described in S3 is an optical demodulation method.

[0045] Specifically, regarding the electrical demodulation method and the optical demodulation method, the electrical demodulation method is low-cost and simple, but susceptible to electromagnetic interference; the optical demodulation method is immune to electromagnetic interference, but is expensive and complex. The choice of demodulation method depends on the application requirements. This example uses a quartz tuning fork and the electrical demodulation method.

[0046] Example 2

[0047] This embodiment 2 is based on the device set up according to the method of embodiment 1.

[0048] like Figure 2 As shown, this embodiment of the invention provides a non-contact in-situ monitoring device for dissolved gases in oil. An example of the device for measuring dissolved acetylene in oil is as follows: a modulation module 1, an excitation light source 2, a collimator 3, an oil sample cell 4, a focusing lens 5, a tuning fork 6, and a signal demodulation and processing system 7.

[0049] The modulation module 1 is used to modulate the excitation light source 2. The oil sample pool 4 is filled with transformer oil containing dissolved acetylene. The light beam emitted from the excitation light source 2 is collimated by the collimator 3 and enters the oil sample pool 4 from the light-transmitting end. After being absorbed by the dissolved gas in the oil, it exits from the other light-transmitting end of the oil sample pool 4 and is finally focused onto the surface of the tuning fork 6 by the focusing lens 5. The vibration signal of the tuning fork 6 is demodulated by the signal demodulation and processing system 7 and its harmonic signal amplitude is extracted to retrieve the gas concentration information.

[0050] In this example, the method for preparing the dissolved acetylene oil sample is as follows: acetylene standard gas is introduced into the standard oil sample, and the mixture is stirred with a magnetic stirrer for more than two hours. The concentration is then degassed and detected by gas chromatography, and found to be 5.2 ppm.

[0051] The oil sample pool 4 is also equipped with an oil inlet and an oil outlet, which are used for oil inlet and outlet respectively. In this example, a peristaltic pump is used to control the automatic inlet and outlet of the oil sample.

[0052] The tuning fork 6 can operate in both normal and low-pressure environments. Under low pressure, its quality factor can be improved, thereby increasing its detection sensitivity (of course, an additional pressure control unit is required to operate in a low-pressure environment).

[0053] In this embodiment of the invention, a standard quartz tuning fork is used, which operates under normal pressure, has a resonant frequency of 32.768kHz, a quality factor of 9000, and an operating ambient temperature of 28 degrees Celsius.

[0054] In this embodiment of the invention, a stainless steel air chamber is also used to encapsulate the tuning fork, which serves to stabilize the working environment of the tuning fork. At the same time, a shock-absorbing device is used to reduce the interference of external vibration environment on the measuring device. A high-transmittance window is installed on the stainless steel air chamber. The material is calcium fluoride, which has high transmittance in the near-infrared band of 1450-1600nm. The transmittance in the 1532.8nm band used in this example is 92%.

[0055] In this embodiment of the invention, an electrical demodulation method based on the quartz piezoelectric effect is used.

[0056] In this embodiment of the invention, lock-in amplification technology is used to extract the harmonic signal amplitude of the tuning fork vibration signal.

[0057] The above embodiments are merely examples. For instance, for different target gases, the laser wavelength can be selected in advance, and the concentration of different target gases in oil can be detected by changing the wavelength of the excitation light source (similarly, the gas dissolution absorption spectra of different gases in oil, due to the principle of like dissolves like, have a decreased electron cloud density and a smaller intermolecular distance, resulting in a weakening of stretching vibrations, and the absorption spectral lines will be redshifted and broadened compared to the gas phase). The excitation light can be modulated by generating a modulation signal through a signal generator and loading it onto the laser, or it can be modulated by external methods such as a chopper. For aspects not described in detail in this invention (such as specific electrical demodulation methods, optical demodulation methods, etc.), the photothermal elastic technology for detecting gas concentration in air, known in the prior art, can be referred to. The specific demodulation method can be selected based on the material of the tuning fork (electrical demodulation is low-cost and simple, but susceptible to electromagnetic interference; optical demodulation is immune to electromagnetic interference, but is high-cost and complex; the actual demodulation method used can be selected according to application requirements).

[0058] Those skilled in the art will readily understand that the above description is merely 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 scope of protection of the present invention.

Claims

1. A non-contact in-situ monitoring method for dissolved acetylene in transformer oil, characterized in that, Includes the following steps: The emission wavelength of the excitation light source was selected as 1532.8 nm based on the peak wavelength of the absorption spectrum of dissolved acetylene in the oil. This absorption spectrum is red-shifted and broadened compared to that in the gas phase. The protective oil for the power equipment to be tested was filled into an oil sample cell that is transparent at both ends. Then, the modulated collimated laser was incident on the oil sample cell from the transparent end for in-situ monitoring. The beam emitted from the other transparent end of the oil sample cell irradiated the surface of the tuning fork. The vibration signal of the tuning fork, based on the photothermoelastic effect and resonance enhancement effect, can reflect the change in light intensity caused by the absorption of dissolved acetylene in the protective oil for the power equipment. By demodulating the vibration signal of the tuning fork and extracting the harmonic signal amplitude, the concentration information of acetylene contained in the protective oil for the power equipment to be tested can be obtained by inversion. The protective oil of the power equipment under test is the transformer oil under test; The oil sample pool is equipped with an oil inlet and an oil outlet, which are used for oil intake and oil discharge, respectively. The protective oil for the electrical equipment being tested, which fills the oil sample pool, is either in a static state or in a flow state that is flowing at a preset flow rate.

2. The non-contact in-situ monitoring method for dissolved acetylene in transformer oil as described in claim 1, characterized in that, The light beam emitted from the oil sample pool specifically illuminates the middle of the root of the two arms of the tuning fork.

3. The non-contact in-situ monitoring method for dissolved acetylene in transformer oil as described in claim 1, characterized in that, The modulation frequency of the collimated laser corresponds to the resonance frequency of the tuning fork.

4. The non-contact in-situ monitoring method for dissolved acetylene in transformer oil as described in claim 1, characterized in that, The tuning fork is a tuning fork made of piezoelectric material, or a tuning fork made of non-piezoelectric material; When the tuning fork is made of piezoelectric material, the demodulation is performed using electrical demodulation or optical demodulation. When the tuning fork is made of a non-piezoelectric material, the demodulation is performed using an optical demodulation method.

5. The non-contact in-situ monitoring method for dissolved acetylene in transformer oil as described in claim 1, characterized in that, The tuning fork is located in an environment with normal air pressure or a low air pressure environment; When the tuning fork is in a low-pressure air environment, it is placed in a pressure vessel with a high-transmittance window, and the light beam emitted from the oil sample cell irradiates the surface of the tuning fork through the high-transmittance window; the high-transmittance window has a transmittance of not less than 90% at the corresponding wavelength of the laser.

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