Non-contact in-situ monitoring method and device for gas dissolved in oil

Abstract

The invention belongs to the technical field of detection of gas in oil, and discloses a non-contact in-situ monitoring method and device for gas dissolved in oil, and the in-situ monitoring method comprises the following steps: aiming at the type of target detection gas, according to the absorption spectral line of the target detection gas dissolved in oil, selecting the emergent laser wavelength of an excitation light source; the method comprises the following steps: filling to-be-detected power equipment protection oil into an oil sample pool with two light-transmitting ends; then, the modulated collimated laser is emitted into an oil sample pool, a light beam emitted by the oil sample pool is irradiated to the surface of a tuning fork, and a vibration signal of the tuning fork can reflect a light intensity variation caused by absorption of dissolved gas in the power equipment protection oil based on a photoinduced thermoelastic effect and a resonance enhancement effect; the harmonic signal amplitude is extracted by demodulating the vibration signal of the tuning fork, and then the concentration information of the gas contained in the to-be-detected power equipment protection oil can be obtained through inversion. According to the invention, the concentration of the dissolved gas in the oil can be directly detected in situ under the conditions of no degassing and no contact between the detection unit and the oil sample.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas detection in oil, and more specifically, relates to a non-contact in-situ monitoring method and device for dissolved gas in oil. Background Art

[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 power 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 and large-capacity oil-filled electrical equipment has increased, becoming 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 very necessary. At present, the most effective method is to judge by the absolute content and relative growth of characteristic gases dissolved in the insulating oil.

[0003] Most of the current gas detection technologies in oil require the use of oil-gas separation units to degas the dissolved gas in the oil. This process is not only very time-consuming and unable to provide timely warning of equipment failures, but its performance is also restricted by the gas content of the insulating oil. For example, when the gas content of the insulating oil is low, the characteristic gas content removed by the oil-gas separation unit is low, the response signal of some monitoring devices cannot meet the requirements, and the reliability of the monitoring data is low; for example, when the gas content of the insulating oil is high, especially when the equipment discharge causes a sudden increase in gas and oil-gas mixing occurs, the degassing units of some monitoring devices cannot work normally and cannot reflect the equipment status in time. Degassing units are generally divided into two types according to their working principles: vacuum degassing and dynamic headspace degassing. When dynamic headspace degassing is used, the insulating oil inevitably introduces external air, resulting in an increase in the gas content of the return oil, affecting the safety of the equipment; when vacuum degassing is used, especially when piston pumps and membrane pumps are used, the pump often has poor sealing due to frequent reciprocating motion, resulting in the device being unable to work normally, and even oil leakage, affecting the safety of the equipment. Although hollow-core fiber-based photothermal spectroscopy has been applied to the in-situ detection of dissolved gases in oil, the core of the hollow-core fiber is very thin (on the order of microns), which results in a very long time (greater than 1 hour) for the oil to diffuse into the core. Therefore, this method is also difficult to monitor and warn of equipment failures in a timely manner.

[0004] With the increasing attention paid to environmental protection, there have been many reports on the detection technology of gas components in the air in the field of atmospheric environment monitoring. Taking the currently commonly used photoacoustic spectroscopy technology as an example, the basic principle of photoacoustic spectroscopy technology is that after the modulated laser irradiates the gas to be measured, the gas to be measured will cause changes in the temperature field in the process of absorbing and releasing laser energy. The change in the temperature field in the cavity will cause changes in the sound field. The change in the sound field can be captured by a highly sensitive microphone or quartz tuning fork to invert the concentration information of the gas to be measured. However, if the photoacoustic spectroscopy technology is applied to the in-situ monitoring of dissolved gas in oil, the microphone will inevitably come into contact with the oil, which will cause the sensitivity of the microphone to deteriorate sharply, and it is difficult to ensure long-term stability.

[0005] Therefore, there is an urgent need for a non-contact in-situ monitoring method and device for dissolved gas in oil without degassing. Summary of the invention

[0006] In view of the above defects or improvement needs of the prior art, the object 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 contact between the detection unit and the oil sample.

[0007] To achieve the above-mentioned purpose, according to one aspect of the present invention, a non-contact in-situ monitoring method for dissolved gas in oil is provided, comprising the following steps: for the type of target detection gas, the wavelength of the output laser of the excitation light source is selected according to the absorption spectrum of the target detection gas dissolved in the oil, and the absorption spectrum is red-shifted and broadened compared with that in the gas phase; the protective oil of the power equipment to be tested is filled in an oil sample pool with light transmittance at both ends; then, the modulated collimated laser is incident into the oil sample pool from the light transmittance end of the oil sample pool, and the light beam emitted from the other light transmittance end of the oil sample pool is irradiated onto the surface of the tuning fork, and the vibration signal of the tuning fork can reflect the change in light intensity caused by the absorption of dissolved gas in the protective oil of the power equipment based on the photothermoelastic effect and the resonance enhancement effect; the concentration information of the gas contained in the protective oil of the power equipment to be tested can be inverted by extracting the amplitude of the harmonic signal by demodulating 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 is irradiated to the middle of the roots of the two vibration 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 a piezoelectric material, or a tuning fork made of a non-piezoelectric material;

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

[0012] When the tuning fork is made of non-piezoelectric material, the demodulation is performed by 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, the tuning fork is placed in a pressure container with a high-transmittance window, and the light beam emitted from the oil sample pool is irradiated to 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 of the electric equipment to be tested filled in the oil sample pool is in a static state or in a flowing state flowing at a preset flow rate;

[0017] Preferably, the protective oil of the electric power equipment to be tested is transformer oil to be tested.

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

[0019] The oil sample pool is used to be filled with protective oil for the electric power equipment to be tested;

[0020] The laser beam emitted by the excitation light source is modulated and incident on the collimator to obtain modulated collimated laser light; the wavelength of the laser beam is selected according to the type of target detection gas and the absorption spectrum of the target detection gas dissolved in the oil, and 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 to extract the amplitude of the harmonic signal, thereby inverting the concentration information of the gas contained in the protective oil of the power equipment to be tested.

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

[0024] Through the above technical scheme conceived by the present invention, compared with the prior art, the present invention is the first to transfer the photothermal elastic technology for detecting gas concentration in the air to the detection of dissolved gas in oil, avoiding the degassing treatment required for the existing detection of gas in oil. Since no degassing treatment is required, the present invention can avoid the degassing treatment being restricted by the gas content and the working conditions of the degassing device.

[0025] For power equipment (especially high-voltage substation equipment, such as transformers, high-voltage shunt reactors, etc.), power equipment protection oil plays an important role in equipment safety (among which transformers belong to the one with the highest safety level requirements). The present invention realizes non-contact in-situ monitoring of dissolved gases in oil based on photothermoelastic technology, which is obviously different from the degassing detection method mostly adopted in the prior art. Different from the photothermoelastic effect in gas, the electron cloud density of the gas dissolved in oil decreases due to the principle of like dissolves like, and at the same time, the molecular distance decreases, resulting in the weakening of the stretching vibration effect, and the absorption spectrum is red-shifted and broadened compared to the gas phase. At the same time, the tuning fork detection unit designed by the present invention is outside the oil sample pool and adopts a non-contact working mode, which also avoids the difficulty of the detection unit working in an oil environment. The present invention overcomes the problems of changes in gas absorption spectra and the inability of the detection unit to work in an oil environment.

[0026] The present invention can perform non-contact in-situ monitoring of dissolved gases in 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, and fault warning can be quickly and timely performed; (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 is not in contact with the oil sample, avoiding the influence of the oil on the performance of the tuning fork and also avoiding the contamination of the tuning fork material to the oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure is a flow chart of the non-contact in-situ monitoring method of dissolved gas in oil according to the present invention.

[0028] Figure 2 It is a schematic structural diagram of the non-contact in-situ monitoring device for dissolved gas in oil of the present invention.

[0029] Figure 2 The meanings of the various reference numerals are as follows: 1 is a modulation module, 2 is an excitation light source, 3 is a collimator, 4 is an oil sample pool (translucent at both ends), 5 is a focusing lens, 6 is a tuning fork, and 7 is a signal demodulation and processing system. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] In general, the non-contact in-situ monitoring method of dissolved gas in oil of the present invention is that after the excitation light is modulated, the light beam is collimated by a collimator and incident into the oil sample pool, and then emitted from the oil sample pool after being absorbed by the dissolved gas in the oil (the excitation light source is used to excite the gas dissolved in the oil to produce absorption; the laser is incident into the oil sample pool, and the dissolved gas in the oil absorbs the light energy, resulting in a change in the intensity of the emitted light), and finally converged to the surface of the tuning fork (it can be at any position, but the best effect is to be incident on the middle of the roots of the two Y-shaped arms of the tuning fork), and the concentration information of the gas is inverted 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 pool, a tuning fork, a signal demodulation and processing system (a separate modulation module may be optionally provided to modulate the excitation laser).

[0032] Take the No. 25 transformer oil of the national standard 750kv transformer as an example:

[0033] Example 1

[0034] like Figure 1 As shown, an embodiment of the present invention provides a non-contact in-situ monitoring method for dissolved gas in oil, which is used for detecting dissolved acetylene in oil as follows, including: an excitation light source 2, a collimator 3, an oil sample pool 4, and a tuning fork 6, wherein the oil sample pool 4 is filled with transformer oil dissolved with the gas to be tested, the excitation light source 2 is used to excite the acetylene dissolved in the oil to produce absorption, the collimator 3 is used to collimate the light beam emitted by the excitation light source and then inject it into the oil sample pool, and the tuning fork 6 detects the light intensity change caused by the absorption of dissolved acetylene based on the photothermoelastic effect and the resonance enhancement effect; the in-situ monitoring method includes:

[0035] S1. After the excitation light is modulated, the light beam is collimated and incident on the oil sample pool. The dissolved gas in the oil absorbs the light energy, causing the output light intensity to change;

[0036] S2, the light beam emitted from the oil sample pool is irradiated to the surface of the tuning fork and 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 light source 2 is selected according to the absorption spectrum of acetylene dissolved in oil. In the case of acetylene dissolved in oil, due to the principle of like dissolving like, the electron cloud density decreases, and the molecular distance decreases, which weakens the stretching vibration effect, and the absorption spectrum is red-shifted and broadened compared with that in the gas phase. In the example, the excitation light source 2 is a DFB laser with a wavelength of 1532.8nm, which corresponds to the peak wavelength of the absorption spectrum of acetylene dissolved in oil.

[0039] Specifically, in S1, the excitation light source 2 can generate a modulation signal through a signal generator and load it onto the laser for modulation, or it can be modulated by external means such as a chopper. In this example, a signal generator is used to generate a 32.768kHz sine wave to modulate the drive 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.

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

[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, the demodulation method in S3 is an electrical demodulation method or an optical demodulation method;

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

[0045] Specifically, for the electrical demodulation method and the optical demodulation method, the electrical demodulation method has low cost and a simple system, but is susceptible to electromagnetic interference; the optical demodulation method is immune to electromagnetic interference, but has high cost and a complex system. The actual demodulation method can be selected according to application requirements. In this example, a quartz tuning fork and an electrical demodulation method are used.

[0046] Example 2

[0047] This embodiment 2 is a device configured based on the method of embodiment 1.

[0048] like Figure 2 As shown, an embodiment of the present invention provides a non-contact in-situ monitoring device for dissolved gas in oil, and an example of the device for measuring dissolved acetylene in oil is as follows, comprising: a modulation module 1, an excitation light source 2, a collimator 3, an oil sample pool 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 dissolved with acetylene. The light beam emitted by the excitation light source 2 is collimated by the collimator 3 and then incident on the oil sample pool 4 from the light-transmitting end of the oil sample pool. After being absorbed by the dissolved gas in the oil, it is emitted from the other light-transmitting end of the oil sample pool 4 and finally converged by the focusing lens 5 to the surface of the tuning fork 6. 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 invert the gas concentration information.

[0050] In this example, the preparation method of the dissolved acetylene oil sample is to introduce acetylene standard gas into the standard oil sample, stir it with a magnetic stirrer for more than two hours, and then degas and detect the concentration of 5.2ppm by gas chromatography.

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

[0052] The tuning fork 6 can work in both normal pressure environment and low pressure environment. Its quality factor can be improved under low pressure, thereby improving its detection sensitivity (of course, working in a low pressure environment requires an additional pressure control unit).

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

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

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

[0056] In the embodiment of the present invention, a phase-locked amplification technology is used to extract the harmonic signal amplitude of the tuning fork vibration signal.

[0057] The above embodiments are only examples. For example, for different target gases, the wavelength of the laser can be selected in advance, and the concentration of different target gases in the oil can be detected by changing the wavelength of the excitation light source (similarly, the gas dissolution absorption spectrum of different gases in the oil, due to the principle of like dissolves like, the electron cloud density decreases, and the molecular distance decreases, resulting in a weakened stretching vibration effect, and the absorption spectrum will be red-shifted and broadened compared to the gas phase); the excitation light can be modulated by a signal generator to generate a modulation signal loaded on the laser for modulation, or it can be modulated by an external method such as a chopper. Parts not described in detail in the present invention (such as specific electrical demodulation methods, optical demodulation methods, etc.) can be referred to the photothermoelastic technology for detecting gas concentration in the air known in the prior art, and the specific demodulation method can be selected according to the material of the tuning fork (the electrical demodulation method has low cost and a simple system, but is susceptible to electromagnetic interference; the optical demodulation method is immune to electromagnetic interference, but has high cost and a complex system; which demodulation method is actually used can be selected according to application requirements).

[0058] It will be easily understood by those skilled in the art that 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 in the protection scope of the present invention.

Claims

1. A non-contact in-situ monitoring method for dissolved gas in oil, characterized in that: The following steps are involved: For the type of target detection gas, the wavelength of the output laser of the excitation light source is selected according to the absorption spectrum of the target detection gas dissolved in the oil, and the absorption spectrum is red-shifted and broadened compared with that in the gas phase; the protective oil of the power equipment to be tested is filled in an oil sample pool with light transmittance at both ends; then, the modulated collimated laser is incident into the oil sample pool from the light transmittance end of the oil sample pool, and the light beam emitted from the other light transmittance end of the oil sample pool is irradiated to the surface of the tuning fork, and the vibration signal of the tuning fork can reflect the change in light intensity caused by the absorption of dissolved gas in the protective oil of the power equipment based on the photothermoelastic effect and the resonance enhancement effect; the concentration information of the gas contained in the protective oil of the power equipment to be tested can be inverted by extracting the amplitude of the harmonic signal by demodulating the vibration signal of the tuning fork.

2. The non-contact in-situ monitoring method for dissolved gas in oil according to claim 1, characterized in that: The light beam emitted from the oil sample pool is specifically irradiated to the middle of the roots of the two vibration arms of the tuning fork.

3. The non-contact in-situ monitoring method for dissolved gas in oil according to claim 1, characterized in that: The modulation frequency of the modulated collimated laser corresponds to the resonance frequency of the tuning fork.

4. The non-contact in-situ monitoring method for dissolved gas in oil according to claim 1, characterized in that: The tuning fork is a tuning fork made of a piezoelectric material, or a tuning fork made of a non-piezoelectric material; When the tuning fork is made of piezoelectric material, the demodulation is performed by electrical demodulation or optical demodulation; When the tuning fork is made of non-piezoelectric material, the demodulation is performed by an optical demodulation method.

5. The non-contact in-situ monitoring method for dissolved gas in oil according to claim 1, characterized in that: The environment in which the tuning fork is located is a normal pressure air environment or a low pressure air environment; When the tuning fork is in a low-pressure air environment, the tuning fork is placed in a pressure container with a high-transmittance window, and the light beam emitted from the oil sample pool is irradiated to 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%.

6. The non-contact in-situ monitoring method for dissolved gas in oil according to claim 1, characterized in that: The oil sample pool is provided with an oil inlet and an oil outlet, which are used for oil inlet and oil outlet respectively; The protective oil of the electric equipment to be tested filled in the oil sample pool is in a static state or in a flowing state flowing at a preset flow rate; Preferably, the protective oil of the electric power equipment to be tested is transformer oil to be tested.

7. A non-contact in-situ monitoring device for dissolved gas in oil, characterized in that: The device is used to perform the non-contact in-situ monitoring method of dissolved gas in oil as claimed in any one of claims 1 to 6, and comprises an excitation light source, a signal demodulation and processing system, and a collimator, an oil sample pool, a focusing lens, and a tuning fork arranged in sequence along the outgoing light path of the excitation light source; wherein, The oil sample pool is used to be filled with protective oil for the electric power equipment to be tested; The laser beam emitted by the excitation light source is modulated and incident on the collimator to obtain modulated collimated laser light; the wavelength of the laser beam is selected according to the type of target detection gas and the absorption spectrum of the target detection gas dissolved in the oil, and the absorption spectrum is red-shifted and broadened compared to that in the gas phase; The focusing lens is used to converge the light beam emitted from the oil sample pool onto the surface of the tuning fork; The signal demodulation and processing system is used to demodulate the vibration signal of the tuning fork to extract the amplitude of the harmonic signal, thereby inverting the concentration information of the gas contained in the protective oil of the power equipment to be tested.

8. The non-contact in-situ monitoring device for dissolved gas in oil as claimed in claim 7, characterized in that: The modulation is performed by generating a modulation signal through a signal generator and loading the modulation signal onto the excitation light source, or by modulating the laser beam emitted by the excitation light source through a chopper.

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