A concentration detection system for dissolved gas in transformer oil

Abstract

The present invention relates to a concentration detection system for dissolved gas in transformer oil. The detection system comprises: an industrial computer, a signal generation module, a laser light source module, a six-core optical cable, a ceramic membrane tube, a microphone, a preamplifier module and a signal acquisition module; the gas molecules dissolved in the transformer oil enter the interior of the ceramic membrane tube through densely distributed micropores on the ceramic membrane tube, and the separated gas molecules absorb laser energy in the ceramic membrane tube to generate a photoacoustic effect to measure the gas concentration. The present invention adopts a ceramic membrane tube that integrates oil and gas separation and photoacoustic excitation functions, and the sensing system does not require an air pump and an air valve, which greatly simplifies the system structure.

Description

Technical Field

[0001] The invention relates to the fields of high voltage and insulation technology and trace gas detection technology, in particular to a concentration detection system for dissolved gas in transformer oil. Background Art

[0002] Insulating oil and insulating cardboard are usually used for insulation inside large power transformers to reduce the size of the transformer. After a long period of operation, the transformer may experience internal faults such as overheating and discharge, which will cause the CH bonds and CC bonds in certain compound molecules of the insulating oil and the internal insulating cardboard to crack and produce a variety of characteristic gases, such as CH4, C2H2, C2H4, C2H6 and other small molecule hydrocarbon gases as well as CO and CO2. These gases will partially dissolve in the insulating oil; by monitoring the content of characteristic gas components, the type of fault that occurs during transformer operation can be analyzed. Therefore, efficiently separating the characteristic gases dissolved in the insulating oil and detecting their concentrations with high sensitivity is the key to achieving real-time online monitoring of the transformer.

[0003] At present, the most commonly used oil-gas separation methods are thin film permeation method, dynamic headspace separation method and vacuum degassing method. The latter two methods have the problems of complex mechanical structure assembly and the need to extract the oil sample from the transformer for detection; while the thin film permeation method has many advantages such as simple structure, convenient maintenance and stable performance. At present, the most commonly used oil dissolved gas separation membranes are polymer membranes and ceramic membranes. The separated oil dissolved gas needs to be measured by sensors (such as electrochemical sensors and semiconductor sensors) or gas detectors (such as gas chromatographs and photoacoustic spectrometers) for concentration measurement. Small-volume and low-cost electrochemical sensors and semiconductor sensors can measure one gas component. In order to achieve simultaneous measurement of multiple gas components, a sensor combination array can be used; however, both sensors have the disadvantage of large cross-interference between multiple gas components. In addition, electrochemical sensors also have the problem of regular replacement due to their short working life when used on site.

[0004] Gas chromatographs have the advantages of being able to measure multiple gas components simultaneously and having high sensitivity, but they also have the problems of consuming carrier gas, which leads to a large maintenance workload and a long warm-up time. Photoacoustic spectroscopy is a background-free absorption spectroscopy technique that measures the intensity of sound waves generated by the gas due to the absorption of light energy to invert the concentration of the gas to be measured. Compared with the above-mentioned non-optical measurement methods, photoacoustic spectrometers based on the Lambert-Beer absorption law have significant advantages such as no need for carrier gas, fast response speed, high sensitivity and good selectivity. In recent years, they are gradually replacing traditional gas chromatographs. However, current photoacoustic spectrometers have some problems in field applications: (1) The solution of combining infrared thermal radiation light source with filter cannot fundamentally solve the interference problem between gas components dissolved in complex oil due to its wide spectral coverage; (2) The structure of the oil circuit, gas circuit and optical system in the photoacoustic spectrometer system is complex. These problems that arise in practical applications make it difficult for photoacoustic spectrometers to be widely promoted and used. Summary of the invention

[0005] The purpose of the present invention is to provide a concentration detection system for dissolved gas in transformer oil, so as to solve the problems of low measurement accuracy and complex structure of the existing photoacoustic spectrometer.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A concentration detection system for dissolved gas in transformer oil, comprising: an industrial computer, a signal generation module, a laser light source module, a six-core optical cable, a ceramic membrane tube, a microphone, a preamplifier module and a signal acquisition module;

[0008] One end of the industrial computer is connected to one end of the signal generating module, the other end of the signal generating module is connected to the laser light source module, the other end of the laser light source module is connected to one end of the six-core optical cable, the other end of the six-core optical cable is connected to one end of the ceramic membrane tube, the other end of the ceramic membrane tube is connected to one end of the microphone, the other end of the microphone is connected to one end of the preamplifier module, the other end of the preamplifier module is connected to one end of the signal acquisition module; the other end of the signal acquisition module is connected to the other end of the industrial computer; the signal generating module is used to modulate the current of the laser light source module; the laser light source module is used to output laser light and transmit it to the The interior of the ceramic diaphragm tube; the ceramic diaphragm tube is immersed in transformer oil, and a plurality of micropores are distributed on the outer surface of the ceramic diaphragm tube; the micropores are used for the gas to be tested dissolved in the transformer oil to enter the interior of the ceramic diaphragm tube; the ceramic diaphragm tube is used to generate a gas photoacoustic pressure wave and generate a gas photoacoustic pressure wave signal; the microphone is used to convert the gas photoacoustic pressure wave signal into a photoelectric signal; the preamplifier module is used to amplify the photoelectric signal; the preamplifier module is used to collect the amplified photoelectric signal and transmit the amplified photoelectric signal to the industrial computer; the industrial computer is used to send a control instruction to the signal generating module and extract the second harmonic component of the amplified photoelectric signal, and determine the concentration of the gas to be tested according to the second harmonic component.

[0009] Optionally, the radius of the ceramic membrane tube is less than 5 mm; and the pore size of the micropores is less than 50 nm.

[0010] Optionally, the laser light source module is a near-infrared distributed feedback laser; the near-infrared distributed feedback laser includes six near-infrared lasers; the wavelengths of the six near-infrared lasers are 1653nm, 1680nm, 1627nm, 1530nm, 1567nm and 1580nm respectively; the six wavelengths are used to measure methane gas, ethane gas, ethylene gas, acetylene gas, carbon monoxide gas and carbon dioxide gas respectively.

[0011] Optionally, the six-core optical cable includes six single-mode optical fibers; the model of the single-mode optical fibers is G652.

[0012] Optionally, the microphone is a micro-electromechanical system (MEMS) microphone having a sensitivity higher than 10 mV / Pa.

[0013] Optionally, the sampling rate of the signal sampling module is 10 kHz.

[0014] Optionally, the industrial computer is an STM32 single-chip microcomputer.

[0015] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the present invention provides a concentration detection system for dissolved gas in transformer oil, wherein a ceramic membrane tube is immersed in transformer oil, and the dissolved gas in the oil enters the interior of the ceramic membrane tube through the micropores on the ceramic membrane tube, and the separated gas molecules absorb laser energy in the ceramic membrane tube to produce a photoacoustic effect, and the gas concentration is accurately calculated, thereby monitoring the gas concentration in real time. The present invention adopts a ceramic membrane tube that integrates oil and gas separation and photoacoustic excitation functions, and does not require an air pump and an air valve, which greatly simplifies the system structure; at the same time, the use of a full laser solution can also greatly reduce cross-interference between gases; in addition, the transformer oil will not come into contact with the ambient air, avoiding the risk of water molecules in the air entering the oil to increase the concentration of micro-water and cause the insulation performance of the transformer oil to deteriorate. The gas concentration detection system provided by the present invention has a simple structure and has many advantages such as high precision, small size, low cost, low power consumption and fast response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 This is a structural diagram of the concentration detection system of dissolved gas in transformer oil provided by the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] The object of the present invention is to provide a concentration detection system for dissolved gas in transformer oil, which can improve the measurement accuracy of gas concentration and simplify the structure of the detection system.

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1 The structure diagram of the concentration detection system of dissolved gas in transformer oil provided by the present invention is as follows: Figure 1As shown, a concentration detection system for dissolved gas in transformer oil includes: an industrial computer 1, a signal generating module 2, a laser light source module 3, a six-core optical cable 4, a ceramic membrane tube 5, a microphone 6, a preamplifier module 7 and a signal acquisition module 8;

[0022] One end of the industrial computer 1 is connected to one end of the signal generating module 2, the other end of the signal generating module 2 is connected to the laser light source module 3, the other end of the laser light source module 3 is connected to one end of the six-core optical cable 4, the other end of the six-core optical cable 4 is connected to one end of the ceramic diaphragm tube 5, the other end of the ceramic diaphragm tube 5 is connected to one end of the microphone 6, the other end of the microphone 6 is connected to one end of the preamplifier module 7, the other end of the preamplifier module 7 is connected to one end of the signal acquisition module 8; the other end of the signal acquisition module 8 is connected to the other end of the industrial computer 1.

[0023] The signal generating module 2 is used for current modulation of the laser light source module 3; the laser light source module 3 is used for outputting laser light, and transmitting the laser light to the interior of the ceramic membrane tube 5 through the six-core optical cable 4; the ceramic membrane tube 5 is immersed in transformer oil, and a plurality of micropores are distributed on the outer surface of the ceramic membrane tube 5; the micropores are used for the gas to be measured dissolved in the transformer oil to enter the interior of the ceramic membrane tube 5; the ceramic membrane tube 5 is used for generating gas photoacoustic pressure waves and generating gas photoacoustic pressure wave signals; the microphone 6 is used for converting the gas photoacoustic pressure wave signals into photoelectric signals; the preamplifier module 7 is used for amplifying the photoelectric signals; the preamplifier module 7 is used for collecting the amplified photoelectric signals and transmitting the amplified photoelectric signals to the industrial computer 1; the industrial computer 1 is used for sending control instructions to the signal generating module 2 and extracting the second harmonic component of the amplified photoelectric signal, and determining the concentration of the gas to be measured according to the second harmonic component.

[0024] The industrial computer 1 sends a control instruction to the signal generating module 2 to control parameters such as frequency and modulation depth. The sinusoidal modulation signal output by the signal generating module 2 is input to the laser light source module 3 to modulate the current of six near-infrared lasers in turn. The six-channel laser output by the laser light source module 3 is transmitted to the inside of the ceramic membrane tube 5 through the six-core optical cable 4. The gas molecules dissolved in the transformer oil enter the inside of the ceramic membrane tube 5 through the densely distributed micropores on the ceramic membrane tube 5. The separated gas molecules absorb the light energy of the modulated laser and then transition to the high energy level of the vibration-rotation energy level. , the gas molecules in the excited state convert energy into heat energy by non-radiative transition, and the gas inside the sealed ceramic membrane tube 5 expands and contracts, thereby generating gas photoacoustic pressure waves; the microphone 6 fixed at the other end of the ceramic membrane tube 5 converts the photoacoustic pressure wave signal into an electrical signal, the preamplifier module 7 amplifies the signal and inputs it to the analog signal input end of the signal acquisition module 8, and the signal acquisition module 8 transmits the signal to the industrial computer 1; the signal processing program in the industrial computer 1 extracts the second harmonic component of the photoacoustic signal, and finally calculates the concentration of the gas to be measured.

[0025] Since the diameter of oil molecules is larger than that of gas molecules, the aperture of the micropores is less than 50nm to ensure the separation of gas molecules from transformer oil. In practical applications, the ceramic membrane tube 5 serves as both an oil-gas separation component and a photoacoustic cavity. The radius of the ceramic membrane tube 5 is 2mm, the length is 20mm, and the aperture of the micropores is 10nm.

[0026] The core of the signal generation module 2 is a field programmable gate array (FPGA) chip and a digital-to-analog converter, which is used to generate a sinusoidal voltage signal with a frequency of 500 Hz. The laser light source module 3 includes six near-infrared distributed feedback (DFB) lasers with wavelengths of 1653nm, 1680nm, 1627nm, 1530nm, 1567nm and 1580nm, which are used to measure methane, ethane, ethylene, acetylene, carbon monoxide and carbon dioxide gases respectively.

[0027] The six-core optical cable 4 is mainly composed of six G652 single-mode optical fibers; the microphone 6 is a MEMS microphone 6 with a sensitivity higher than 10 mV / Pa; and the sampling rate of the signal acquisition module 8 is 10 kHz.

[0028] The present invention adopts a ceramic membrane tube integrating the functions of oil-gas separation and photoacoustic excitation, does not require an air pump and an air valve, and greatly simplifies the system structure.

[0029] By immersing the ceramic membrane tube into the transformer oil, real-time monitoring of dissolved gases in the oil can be achieved. The use of a full laser solution can also significantly reduce cross-interference between gases.

[0030] In addition, the transformer oil will not come into contact with the ambient air, thus avoiding the risk of water molecules in the air entering the oil and causing the concentration of trace water to increase, resulting in deterioration of the insulation performance of the transformer oil. It has many advantages such as high precision, small size, low cost, low power consumption and fast response speed.

[0031] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0032] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A concentration detection system for dissolved gas in transformer oil, characterized in that: include: Industrial computer, signal generation module, laser light source module, six-core optical cable, ceramic film tube, microphone, preamplifier module and signal acquisition module; One end of the industrial computer is connected to one end of the signal generating module, the other end of the signal generating module is connected to the laser light source module, the other end of the laser light source module is connected to one end of the six-core optical cable, the other end of the six-core optical cable is connected to one end of the ceramic diaphragm tube, the other end of the ceramic diaphragm tube is connected to one end of the microphone, the other end of the microphone is connected to one end of the preamplifier module, and the other end of the preamplifier module is connected to one end of the signal acquisition module; the other end of the signal acquisition module is connected to the other end of the industrial computer; the signal generating module is used to perform current modulation on the laser light source module; the laser light source module is used to output laser and transmit it to the inside of the ceramic diaphragm tube through the six-core optical cable; the ceramic diaphragm tube is immersed in transformer oil, and a plurality of micropores are distributed on the outer surface of the ceramic diaphragm tube; the micropores are used for the gas to be tested dissolved in the transformer oil to enter the inside of the ceramic diaphragm tube; the ceramic diaphragm tube is used to generate Gas photoacoustic pressure wave, and generate gas photoacoustic pressure wave signal; the six-channel laser output by the laser light source module is transmitted and incident into the ceramic membrane tube through the six-core optical cable, and the gas molecules dissolved in the transformer oil enter the ceramic membrane tube through the densely distributed micropores on the ceramic membrane tube. The separated gas molecules absorb the light energy of the modulated laser and then transition to the high energy level of the vibration-rotation energy level. The gas molecules in the excited state convert the energy into heat energy by non-radiative transition. The gas inside the closed ceramic membrane tube expands and contracts due to heat and cold, thereby generating gas photoacoustic pressure wave; the microphone is used to convert the gas photoacoustic pressure wave signal into a photoelectric signal; the preamplifier module is used to amplify the photoelectric signal; the preamplifier module is used to collect the amplified photoelectric signal and transmit the amplified photoelectric signal to the industrial computer; the industrial computer is used to send the control instruction to the signal generating module and extract the second harmonic component of the amplified photoelectric signal, and determine the concentration of the gas to be measured according to the second harmonic component; The radius of the ceramic membrane tube is less than 5 mm; the pore size of the micropores is less than 50 nm; The laser light source module is a near-infrared distributed feedback laser; the near-infrared distributed feedback laser includes six near-infrared lasers; the wavelengths of the six near-infrared lasers are 1653nm, 1680nm, 1627nm, 1530nm, 1567nm and 1580nm respectively; the six wavelengths are used to measure methane gas, ethane gas, ethylene gas, acetylene gas, carbon monoxide gas and carbon dioxide gas respectively.

2. The system for detecting the concentration of dissolved gas in transformer oil according to claim 1, characterized in that: The six-core optical cable includes six single-mode optical fibers; the model of the single-mode optical fibers is G652.

3. The concentration detection system of dissolved gas in transformer oil according to claim 1, characterized in that: The microphone is a micro-electromechanical system (MEMS) microphone with a sensitivity higher than 10 mV / Pa.

4. The system for detecting concentration of dissolved gas in transformer oil according to claim 1, characterized in that: The sampling rate of the signal acquisition module is 10 kHz.

5. The concentration detection system of dissolved gas in transformer oil according to claim 1, characterized in that: The industrial computer is an STM32 single-chip microcomputer.

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