A kind of on-line monitoring device and method for dissolved gas in step-by-step main transformer oil

Abstract

The application provides a kind of on-line monitoring device and method for dissolved gas in step-by-step main transformer, and the monitoring device for monitoring gas includes a palladium alloy film hydrogen sensor device for rapid detection of single hydrogen component, a membrane type acetylene detector device for rapid detection of single acetylene component, and a full component monitoring device capable of detecting multiple fault gases.When a slight or moderate fault occurs in the main transformer, the on-line monitoring device first uses the palladium alloy film hydrogen sensor device and the membrane type acetylene detector device for rapid detection and analysis, and then further uses the full component monitoring device for corresponding full component detection and analysis, and according to the analysis result, the 3-out-of-2 switching protection work is accurately performed; when a malignant and serious discharge fault occurs in the main transformer, the application can scientifically and reasonably perform the 3-out-of-2 accurate switching protection work, avoid misjudgment, especially avoid the serious consequences of mis-tripping, and effectively ensure the safe, stable and economic operation of the power grid.

Description

Technical Field

[0001] This invention relates to the field of online monitoring devices for dissolved gases in the oil of large oil-filled power transformers in power grid substations, and in particular to a step-type online monitoring device and method for dissolved gases in main transformer oil. Background Technology

[0002] Currently, the configuration of online dissolved gas monitoring devices in oil has become standard practice for large-scale high-voltage oil-filled power transformers in power grids. These devices can sensitively and reliably detect overheating and discharge faults in oil-filled power transformers by detecting the content and composition ratio of characteristic gases, playing a crucial role in preventing the development of transformer accidents. However, existing online dissolved gas monitoring devices for transformers are mainly online spectroscopic monitoring devices and online chromatographic monitoring devices for dissolved characteristic gases. Both types of online monitoring devices are expensive and operate continuously in a single configuration. During long-term continuous operation, the main detection components inside these devices, such as chromatographic columns, characteristic gas sensors, hydrogen flame detectors, thermal conductivity detectors, and spectroscopic detectors, are prone to attenuation and degradation, affecting the accuracy of the test and the service life of the instrument. Furthermore, the single online detection method may produce erroneous detection data due to the above reasons, leading to false alarms, misjudgments, and other adverse actions, posing a threat to the safe operation of power grid transformers. In particular, existing online dissolved gas monitoring devices do not have trip protection functions in the event of a sudden severe discharge fault inside the transformer.

[0003] During operation, the internal windings and core of an oil-filled main transformer are immersed in transformer oil, which serves as insulation and cooling. When an overheating or discharge fault occurs inside the main transformer, the transformer oil around the fault point will undergo pyrolysis or cracking reactions due to the high temperature energy or discharge energy generated by the fault, producing seven gases that are regularly related to the corresponding fault: methane, ethane, ethylene, acetylene, hydrogen, carbon monoxide, and carbon dioxide. These seven gases are called transformer fault characteristic gases (hereinafter referred to as characteristic gases). The more severe the fault, the faster the gas production rate; the longer the fault duration, the more gas accumulates. These fault characteristic gases will partially dissolve in the transformer oil according to their different solubilities, forming a dynamic equilibrium under certain temperature and pressure conditions. Currently, the configuration of online dissolved gas monitoring devices in the oil of large-scale high-voltage oil-filled power transformers in power grids has become standard practice. These devices can sensitively and reliably detect overheating and discharge faults in oil-filled power transformers by detecting the content and composition ratio of characteristic gases, playing a crucial role in preventing the development of transformer accidents. However, existing online dissolved gas monitoring devices for power transformers are mainly online spectroscopic monitoring devices and online chromatographic monitoring devices. Both types of online monitoring devices are expensive and operate continuously in a single configuration. During long-term continuous operation, the main detection components inside these devices, such as chromatographic columns, characteristic gas sensors, thermal conductivity detectors, and spectroscopic detectors (all gas sensors), are prone to attenuation and degradation, affecting the accuracy of the test and the lifespan of the instrument. Furthermore, the single online detection method may produce erroneous detection data due to the above reasons, leading to false alarms, misjudgments, and other adverse actions, posing a hidden danger to the safe operation of power grid transformers. If a new type of online monitoring device can be invented that overcomes the shortcomings and deficiencies of traditional online monitoring devices for dissolved gases in transformer oil, it will be of great significance to ensuring the safe and economical operation of transformers and power grids. Summary of the Invention

[0004] This invention proposes a step-by-step online monitoring device and method for dissolved gases in main transformer oil. When a main transformer experiences a sudden severe discharge fault, it can scientifically and rationally perform 2 out of 3 protection operations, ensuring timely tripping protection of the main transformer when a serious fault does occur. At the same time, it avoids misjudgment, especially avoiding the serious consequences of false tripping, thus effectively ensuring the safe, stable and economical operation of the power grid.

[0005] The present invention adopts the following technical solution.

[0006] A step-by-step online monitoring device for dissolved gases in main transformer oil includes a palladium alloy thin-film hydrogen sensor (4) for rapid detection of a single hydrogen component, a membrane acetylene detector (10) for rapid detection of a single acetylene component, and a full-component monitoring device (11) capable of detecting multiple fault gases. When a minor or moderate fault occurs in the main transformer, the online monitoring device first performs rapid detection and analysis using the palladium alloy thin-film hydrogen sensor and the membrane acetylene detector, and then further performs corresponding full-component detection and analysis using the full-component monitoring device. Based on the analysis results, it accurately performs 3-to-2 trip protection operation.

[0007] The online monitoring device includes an oil-filled power main transformer body, transformer oil filled in the main transformer body, a micro circulating oil pump, an oil flow sensor, a palladium alloy thin film hydrogen sensor device, a membrane acetylene detector device, a full component monitoring device, a micro variable frequency oil-free air compressor device, a control module, a high-voltage circuit breaker on the main transformer power supply side, and connecting pipe fittings. The full-component monitoring device is one of an online spectral monitoring device or an online chromatographic monitoring device; The oil circuit of the online monitoring device includes the following structure: the lower part of the oil-filled power transformer body (14) is equipped with a main transformer oil outlet, which is connected to one side of the main transformer oil outlet solenoid valve (1) to control the main transformer oil outlet to provide the oil sample for the online monitoring device to perform detection. The upper part of the oil-filled power transformer is equipped with a main transformer oil inlet, which is connected to the main transformer oil inlet valve (13) to allow the return oil after detection by the online monitoring device to circulate to the inside of the main transformer. The other side of the oil outlet solenoid valve is connected in sequence to the micro frequency conversion circulating oil pump (2), transformer oil flow sensor (3), palladium alloy thin film hydrogen sensor device, membrane acetylene detector device oil circuit part, and the oil inlet valve at the upper part of the oil-filled power transformer through a pipeline, and flows back to the inside of the main transformer. The gas path structure of the online monitoring device includes a micro variable frequency oil-free air compressor, an adsorption column, an air storage tank, an air pressure and flow stabilizing valve, an air flow sensor, and a gas path section of a membrane acetylene detector. When the gas path section of the membrane acetylene detector is working, the characteristic gas (23) that permeates from the ceramic diaphragm is carried by the dry compressed air (24) used as the carrier gas to form a mixed gas (25), which passes through the gas path section of the membrane acetylene detector and the online spectral monitoring device / online chromatographic monitoring device in sequence before being discharged. When the micro variable frequency oil-free air compressor is working, it outputs a stable flow rate of dry oil-free air as the carrier gas into the ceramic diaphragm cavity space. The air carries the characteristic gas through the gas path section of the membrane acetylene detector and the online spectral monitoring device / online chromatographic monitoring device in sequence before being discharged.

[0008] The palladium alloy thin-film hydrogen sensor device includes a sensor chip (5) and a transmitter. The sensor chip is located in the center of the pipeline behind the flow sensor at the output end of the micro frequency conversion circulating oil pump, directly measuring the hydrogen content in the transformer oil flowing through the pipeline. The transmitter is installed outside the pipeline to transmit the measurement data of the sensor chip to the control module.

[0009] The membrane acetylene detector device includes a characteristic gas permeation membrane tube assembly and an acetylene detector. The characteristic gas permeation membrane tube assembly includes a characteristic gas permeation annular tube (7) formed by an outer ring tube and an inner ring tube. The outer ring tube is a stainless steel shell, and the inner ring tube is a ceramic diaphragm inner ring tube including a highly permeable Teflon polymer composite membrane, which has the function of selectively permeating characteristic gas components. When transformer oil flows through the inner ring tube of the characteristic gas permeation membrane assembly, it forms a closed space between the inner ring tube and the outer ring tube for permeating fault characteristic gas. The characteristic gas permeation annular pipe is equipped with flanges at both ends, which connect it to other pipelines. A first small tube (6) is installed at one end of the outer ring wall of the characteristic gas permeation annular tube. One end of the first small tube is inserted into the space between the inner and outer ring tubes, and the other end of the first small tube is connected in sequence to a gas flow sensor, a pressure and flow stabilizing valve, an air storage tank, an adsorption column, and a micro variable frequency air compressor (21). A second tube (26) is installed at the other end of the outer ring wall of the characteristic gas permeation annular tube. One end of the second tube is inserted into the space between the inner and outer ring tubes, and the other end of the second tube is connected in sequence to the acetylene detector and the online spectral monitoring device / online chromatographic monitoring device. One end of the characteristic gas permeation annular tube is connected to the output pipe of the micro frequency converter circulating oil pump, and the other end of the characteristic gas permeation annular tube is connected to the oil inlet valve on the upper part of the main transformer. When the transformer oil output by the micro-frequency circulating oil pump flows through the inner ring of the membrane acetylene detector's permeation annular tube, the characteristic gas contained in the transformer oil permeates through the highly permeable Teflon polymer composite membrane into the space between the inner and outer rings of the characteristic gas permeation annular tube. It mixes with the dry, oil-free compressed air that enters through the first small tube of the outer ring of the characteristic gas permeation annular tube. This dry, oil-free compressed air, as the carrier gas, carries the characteristic gas through the second small tube of the outer ring of the characteristic gas permeation annular tube and flows sequentially to the acetylene detector and the online spectrometer / online chromatographic detector for detection.

[0010] The inlet of the online spectral monitoring device / online chromatographic monitoring device is connected to the second small tube, where an acetylene detector is installed. The online spectral monitoring device / online chromatographic monitoring device is used to accurately detect each component of the characteristic gas online.

[0011] The micro variable frequency oil-free air compressor device includes: a micro variable frequency oil-free air compressor, an adsorption column, an air tank, a pressure and flow stabilizing valve, and an air flow sensor; The outlet of the micro variable frequency oil-free air compressor is connected in sequence to the adsorption column (18), the air storage tank (20), the pressure and flow stabilizing valve, and the first small tube of the outer ring of the characteristic gas permeation annular pipe through a pipeline. The adsorption column is filled with filler that can adsorb moisture and impurities in the air. An electric contact pressure gauge is installed on the air storage tank to control the start and stop of the variable frequency oil-free air compressor within a certain pressure range. The compressed air output from the micro variable frequency oil-free air compressor is regulated by the pressure and flow stabilizing valve to form a dry oil-free air flow with the required pressure and flow, which is supplied to the subsequent monitoring device as carrier gas. The air flow sensor transmits the flow data to the control module in real time, and the control module automatically adjusts the pressure and flow stabilizing operation of the pressure and flow stabilizing valve.

[0012] The control module is pre-set with the following parameters: a first setting value for hydrogen content exceeding the standard, a first setting value for acetylene content exceeding the standard, a second setting value for acetylene content exceeding the standard, a second setting value for hydrogen content exceeding the standard, a transformer oil flow setting value, and a compressed air voltage and flow stabilization setting value; the second setting value for acetylene content exceeding the standard is a tripping setting value for a switch due to a malignant and rapid increase in acetylene content; the second setting value for hydrogen content exceeding the standard is a tripping setting value for a switch due to a malignant and rapid increase in hydrogen content. The input terminals of the control module are electrically connected to the output terminals of the palladium alloy thin-film hydrogen sensor, acetylene detector, transformer flow sensor, and compressed air flow sensor, respectively. The output terminals of the control module are electrically connected to the input terminals of the main transformer oil outlet solenoid valve, micro variable frequency circulating oil pump, compressed air pressure and flow stabilizing valve, online spectral monitoring device / online chromatographic monitoring device, and secondary protection device of the main transformer power supply side high voltage circuit breaker, respectively.

[0013] The online monitoring device does not have a vacuum / headspace degassing module installed.

[0014] A step-by-step online monitoring method for dissolved gases in main transformer oil, employing the aforementioned step-by-step online monitoring device for dissolved gases in main transformer oil, is characterized by comprising the following steps; Step S1: Sequentially open the main transformer inlet valve (13), the main transformer outlet solenoid valve (1), and the micro frequency converter circulating oil pump (2). Automatically control the output of the frequency converter circulating oil pump (2) through the transformer oil quantity sensor (3) to maintain a stable circulating oil flow rate within the set range. Step S2: Sequentially open the pressure regulating valve (9) and the micro variable frequency air compressor (21). Through the electric contact pressure gauge (19), automatically adjust the pressure of the air tank (20) to the set range. The air flow sensor (8) automatically controls the pressure regulating valve (9) to adjust the output of oil-free dry compressed air 24 with stable pressure and flow. Step S3: Activate the step-by-step online monitoring device for dissolved gases in the main transformer oil; Step S4: During normal operation, the third-level online spectral monitoring device / online chromatographic monitoring device is in a normal cycle detection state, set to turn on and detect once every 24 hours and then turn off. Step S5: The first-stage palladium alloy thin-film hydrogen sensor (4) and the second-stage membrane acetylene detector (10) are set to the normally open state to detect the single hydrogen component in transformer oil and the single acetylene component in characteristic gas (23), respectively. Step S6: When the palladium alloy thin film hydrogen sensor (4) detects that the hydrogen content in the transformer oil exceeds the first hydrogen setting value, the third-level online spectral monitoring device / online chromatographic monitoring device is activated to further conduct a comprehensive detection of the dissolved characteristic gases (23) in the main transformer oil. Based on the specific proportion of each characteristic gas content, the type and degree of fault are accurately determined. Step S7: When the membrane acetylene detector (10) detects that the content of dissolved acetylene gas in the main transformer oil exceeds the first acetylene setting value, the online online spectral monitoring device / online chromatographic monitoring device is activated to conduct a comprehensive detection of the dissolved characteristic gas (23) in the main transformer oil in order to accurately determine the type and degree of the fault. Step S8: When the membrane acetylene detector (10) and the online spectral monitoring device / online chromatographic monitoring device, which are two different detection methods, simultaneously detect that the acetylene gas content in the dissolved characteristic gas in the transformer oil of the main transformer exceeds the second acetylene setting value, the control module directly controls the tripping of the high-voltage circuit breaker (12) on the power supply side of the main transformer to isolate the main transformer body (14) that has suffered a serious fault from the power grid. Step S9: When either the membrane acetylene detector (10) or the online spectral monitoring device / online chromatographic monitoring device detects that the acetylene gas content in the dissolved characteristic gas of the main transformer oil exceeds the second acetylene setting value, and the palladium alloy thin film hydrogen sensor detects that the hydrogen content in the transformer oil exceeds the second hydrogen setting value, the control module also directly controls the tripping of the high-voltage circuit breaker (12) on the main transformer power supply side.

[0015] This invention proposes a step-by-step online dissolved gas monitoring device for main transformer oil, comprising a palladium alloy thin-film hydrogen sensor, a membrane acetylene detector, an online spectral monitoring device / online chromatographic monitoring device, and their supporting combinations. It eliminates the complex vacuum / headspace degassing module of existing online monitoring devices, reduces a large number of valves and cylinders and other mechanical components, improves the long-term operational reliability of the overall device, and lowers the monitoring cost of the entire system. This is the first of its kind in the field of online dissolved gas monitoring devices for main transformer oil. The palladium alloy thin-film hydrogen sensor rapidly detects a single hydrogen component, and the membrane acetylene detector rapidly detects a single... The online spectral monitoring device / online chromatographic monitoring device can comprehensively detect seven fault characteristic gases. This invention's step-by-step online dissolved gas monitoring device for main transformer oil is innovatively designed as a step-by-step and graded monitoring scheme. It can quickly detect and analyze when the main transformer experiences minor or moderate faults. When the main transformer suddenly experiences a severe discharge fault, it can scientifically and rationally perform accurate tripping protection in a 3-out-of-2 manner, ensuring timely tripping protection when a serious fault does occur, while avoiding misjudgment, especially avoiding the serious consequences of false tripping, thus effectively ensuring the safe, stable, and economical operation of the power grid.

[0016] In this invention, the online monitoring device does not have a vacuum / headspace degassing module installed, which saves costs and is fundamentally different from the online monitoring devices currently widely used.

[0017] The advantages of this invention also include: 1) Innovative online detection method for dissolved gases in stepwise graded oils; In this method, a single sensor and detector that is inexpensive and can quickly detect single hydrogen and single acetylene components are designed as the first step monitoring device, and an online spectral monitoring device or online chromatographic monitoring device with full component detection of characteristic gases is designed as the second step monitoring device. 2) Within the technical scope of oil dissolved gas detection, a scientifically and rationally designed 3-out-of-2 accurate trip protection device and protection method are used to ensure accurate trip protection when a real and sudden malignant discharge fault occurs inside the main transformer, while avoiding serious adverse consequences of false detection and false tripping. Attached Figure Description

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Appendix Figure 1 This is a schematic diagram of the operation of the step-type online dissolved gas monitoring device in main transformer oil according to the present invention; Appendix Figure 2 A schematic diagram of the operation of the first-stage palladium alloy thin-film hydrogen sensor and the second-stage membrane acetylene detector in the monitoring process. Appendix Figure 3 Schematic diagram of a membrane acetylene detector; Appendix Figure 4 A block diagram illustrating the control principle of the control module; Appendix Figure 5 yes Figure 1 A magnified view of a portion of the image; In the diagram: 1-Main transformer oil outlet solenoid valve; 2-Miniature variable frequency circulating oil pump; 3-Transformer oil flow sensor; 4-Palladium alloy thin-film hydrogen sensor; 5-Sensing chip; 6-First small tube; 7-Characteristic gas permeation annular tube; 8-Compressed air flow sensor; 9-Pressure and flow stabilizing valve; 10-Membrane acetylene detector device; 11-Full component monitoring device; 12-Main transformer power supply side high-voltage circuit breaker; 13-Main transformer oil inlet valve; 14-Main transformer body; 15-Transformer oil; 16-Winding; 17-Iron core; 18-Adsorption column; 19-Electrical contact pressure gauge; 20-Gas storage tank; 21-Miniature variable frequency air compressor; 22-Ceramic diaphragm inner annular tube; 23-Characteristic gas; 24-Air; 25-Mixed gas; 26-Second small tube. Detailed Implementation

[0019] As shown in the figure, a step-by-step online monitoring device for dissolved gases in main transformer oil includes a palladium alloy thin-film hydrogen sensor 4 for rapid detection of a single hydrogen component, a membrane acetylene detector 10 for rapid detection of a single acetylene component, and a full-component monitoring device 11 capable of detecting multiple fault gases. When a minor or moderate fault occurs in the main transformer, the online monitoring device first performs rapid detection and analysis using the palladium alloy thin-film hydrogen sensor and the membrane acetylene detector, and then further performs corresponding full-component detection and analysis using the full-component monitoring device. Based on the analysis results, it accurately performs 2 out of 3 trip protection.

[0020] The online monitoring device includes an oil-filled power main transformer body, transformer oil filled in the main transformer body, a micro circulating oil pump, an oil flow sensor, a palladium alloy thin film hydrogen sensor device, a membrane acetylene detector device, a full component monitoring device, a micro variable frequency oil-free air compressor device, a control module, a high-voltage circuit breaker on the main transformer power supply side, and connecting pipe fittings. The full-component monitoring device is one of an online spectral monitoring device or an online chromatographic monitoring device; The oil circuit of the online monitoring device includes the following structure: the lower part of the oil-filled power transformer body 14 is equipped with a main transformer oil outlet, which is connected to one side of the main transformer oil outlet solenoid valve 1 to control the main transformer oil outlet to provide oil samples for the online monitoring device to perform detection. The upper part of the oil-filled power transformer is equipped with a main transformer oil inlet, which is connected to the main transformer oil inlet valve 13 to allow the return oil after detection by the online monitoring device to circulate back to the inside of the main transformer. The other side of the oil outlet solenoid valve is connected in sequence through a pipeline to the oil circuit of the micro frequency conversion circulating oil pump 2, the transformer oil flow sensor 3, the palladium alloy thin film hydrogen sensor device, the membrane acetylene detector device, and the oil inlet valve at the upper part of the oil-filled power transformer, so that the oil flows back to the inside of the main transformer. The gas path structure of the online monitoring device includes a miniature variable frequency oil-free air compressor, an adsorption column, an air storage tank, an air pressure and flow stabilizing valve, an air flow sensor, and a gas path section of a membrane acetylene detector. When the gas path section of the membrane acetylene detector is working, the characteristic gas 23 that permeates from the ceramic diaphragm is carried by the dry compressed air 24, which serves as the carrier gas, to form a mixed gas 25. This mixed gas then passes through the gas path section of the membrane acetylene detector and the online spectral monitoring device / online chromatographic monitoring device in sequence before being discharged. When the miniature variable frequency oil-free air compressor is working, it outputs a stable flow rate of dry oil-free air as the carrier gas into the ceramic diaphragm cavity. The air carrying the characteristic gas passes through the gas path section of the membrane acetylene detector and the online spectral monitoring device / online chromatographic monitoring device in sequence before being discharged.

[0021] The palladium alloy thin-film hydrogen sensor device includes a sensor chip 5 and a transmitter. The sensor chip is located in the center of the pipe behind the flow sensor at the output end of the micro frequency conversion circulating oil pump, directly measuring the hydrogen content in the transformer oil flowing through the pipe. The transmitter is installed outside the pipe and is used to transmit the measurement data of the sensor chip to the control module.

[0022] The membrane-type acetylene detector device includes a characteristic gas permeation membrane tube assembly and an acetylene detector. The characteristic gas permeation membrane tube assembly includes a characteristic gas permeation annular tube 7 formed by an outer ring tube and an inner ring tube. The outer ring tube has a stainless steel shell, and the inner ring tube is a ceramic diaphragm inner ring tube including a highly permeable Teflon polymer composite membrane, which has the function of selectively permeating characteristic gas components. When transformer oil flows through the inner ring tube of the characteristic gas permeation membrane assembly, it forms a sealed space between the inner ring tube and the outer ring tube for permeating fault characteristic gases. The characteristic gas permeation annular pipe is equipped with flanges at both ends, which connect it to other pipelines. A first small tube 6 is installed at one end of the outer ring wall of the characteristic gas permeation annular tube. One end of the first small tube is inserted into the space between the inner and outer ring tubes, and the other end of the first small tube is connected in sequence to a gas flow sensor, a pressure and flow stabilizing valve, an air storage tank, an adsorption column, and a micro variable frequency air compressor 21. A second tube 26 is installed at the other end of the outer ring wall of the characteristic gas permeation annular tube. One end of the second tube is inserted into the space between the inner and outer ring tubes, and the other end of the second tube is connected in sequence to an acetylene detector and an online spectral monitoring device / online chromatographic monitoring device. One end of the characteristic gas permeation annular tube is connected to the output pipe of the micro frequency converter circulating oil pump, and the other end of the characteristic gas permeation annular tube is connected to the oil inlet valve on the upper part of the main transformer. When the transformer oil output by the micro-frequency circulating oil pump flows through the inner ring of the membrane acetylene detector's permeation annular tube, the characteristic gas contained in the transformer oil permeates through the highly permeable Teflon polymer composite membrane into the space between the inner and outer rings of the characteristic gas permeation annular tube. It mixes with the dry, oil-free compressed air that enters through the first small tube of the outer ring of the characteristic gas permeation annular tube. This dry, oil-free compressed air, as the carrier gas, carries the characteristic gas through the second small tube of the outer ring of the characteristic gas permeation annular tube and flows sequentially to the acetylene detector and the online spectrometer / online chromatographic detector for detection.

[0023] The inlet of the online spectral monitoring device / online chromatographic monitoring device is connected to the second small tube, where an acetylene detector is installed. The online spectral monitoring device / online chromatographic monitoring device is used to accurately detect each component of the characteristic gas online.

[0024] The micro variable frequency oil-free air compressor device includes: a micro variable frequency oil-free air compressor, an adsorption column, an air tank, a pressure and flow stabilizing valve, and an air flow sensor; The outlet of the miniature variable frequency oil-free air compressor is connected in sequence via a pipeline to an adsorption column 18, an air storage tank 20, a pressure and flow stabilizing valve, and the first small tube of the outer ring of the characteristic gas permeation annular pipe. The adsorption column is filled with packing material that can adsorb moisture and impurities in the air. An electric contact pressure gauge is installed on the air storage tank to control the start and stop of the variable frequency oil-free air compressor within a certain pressure range. The compressed air output from the miniature variable frequency oil-free air compressor is regulated by the pressure and flow stabilizing valve to form a dry oil-free airflow with the required pressure and flow rate, which is supplied to the subsequent monitoring device as carrier gas. The air flow sensor transmits the flow data to the control module in real time, and the control module automatically adjusts the pressure and flow stabilizing operation of the pressure and flow stabilizing valve.

[0025] The control module is pre-set with the following parameters: a first setting value for hydrogen content exceeding the standard, a first setting value for acetylene content exceeding the standard, a second setting value for acetylene content exceeding the standard, a second setting value for hydrogen content exceeding the standard, a transformer oil flow setting value, and a compressed air voltage and flow stabilization setting value; the second setting value for acetylene content exceeding the standard is a tripping setting value for a switch due to a malignant and rapid increase in acetylene content; the second setting value for hydrogen content exceeding the standard is a tripping setting value for a switch due to a malignant and rapid increase in hydrogen content. The input terminals of the control module are electrically connected to the output terminals of the palladium alloy thin-film hydrogen sensor, acetylene detector, transformer flow sensor, and compressed air flow sensor, respectively. The output terminals of the control module are electrically connected to the input terminals of the main transformer oil outlet solenoid valve, micro variable frequency circulating oil pump, compressed air pressure and flow stabilizing valve, online spectral monitoring device / online chromatographic monitoring device, and secondary protection device of the main transformer power supply side high voltage circuit breaker, respectively.

[0026] The online monitoring device does not have a vacuum / headspace degassing module installed.

[0027] A step-by-step online monitoring method for dissolved gases in main transformer oil, employing the aforementioned step-by-step online monitoring device for dissolved gases in main transformer oil, is characterized by comprising the following steps; Step S1: Sequentially open the main transformer inlet valve 13, the main transformer outlet solenoid valve 1, and the micro frequency converter circulating oil pump 2. The output of the frequency converter circulating oil pump 2 is automatically controlled by the transformer oil quantity sensor 3 to maintain a stable circulating oil flow rate within the set range. Step S2: Sequentially open the pressure stabilizing valve 9 and the micro variable frequency air compressor 21. Through the electric contact pressure gauge 19, automatically adjust the pressure of the air tank 20 to the set range. The air flow sensor 8 automatically controls the pressure stabilizing valve 9 to adjust the output of oil-free dry compressed air 24 with stable pressure and flow. Step S3: Activate the step-by-step online monitoring device for dissolved gases in the main transformer oil; Step S4: During normal operation, the third-level online spectral monitoring device / online chromatographic monitoring device is in a normal cycle detection state, set to turn on and detect once every 24 hours and then turn off. Step S5: The first-stage palladium alloy thin-film hydrogen sensor 4 and the second-stage membrane acetylene detector 10 are set to the normally open state to detect the single hydrogen component in transformer oil and the single acetylene component in characteristic gas 23, respectively. Step S6: When the palladium alloy thin film hydrogen sensor 4 detects that the hydrogen content in the transformer oil exceeds the first hydrogen set value, the third-level online spectral monitoring device / online chromatographic monitoring device is activated to further conduct a comprehensive detection of the dissolved characteristic gas 23 in the main transformer oil. Based on the specific proportion of each characteristic gas content, the type and degree of fault are accurately determined. Step S7: When the membrane acetylene detector 10 detects that the content of dissolved acetylene gas in the main transformer oil exceeds the first acetylene setting value, the online spectral monitoring device / online chromatographic monitoring device is activated to conduct a comprehensive detection of the dissolved characteristic gas 23 in the main transformer oil in order to accurately determine the type and degree of development of the fault. Step S8: When the membrane acetylene detector 10 and the online spectral monitoring device / online chromatographic monitoring device, which are two detectors with different detection methods, simultaneously detect that the acetylene gas content in the dissolved characteristic gas in the main transformer oil exceeds the second acetylene setting value, the control module directly controls the tripping of the high-voltage circuit breaker 12 on the main transformer power supply side, thus isolating the main transformer body 14, which has experienced a serious fault, from the power grid. Step S9: When either the membrane acetylene detector 10 or the online spectral monitoring device / online chromatographic monitoring device detects that the acetylene gas content in the dissolved characteristic gas of the main transformer oil exceeds the second acetylene setting value, and the palladium alloy thin-film hydrogen sensor detects that the hydrogen content in the transformer oil exceeds the second hydrogen setting value, the control module also directly controls the tripping of the high-voltage circuit breaker 12 on the main transformer power supply side.

Claims

1. A step-type online monitoring device for dissolved gases in main transformer oil, characterized in that: The monitoring device for monitoring gases includes a palladium alloy thin-film hydrogen sensor for rapid detection of a single hydrogen component, a membrane acetylene detector for rapid detection of a single acetylene component, and a full-component monitoring device capable of detecting multiple fault gases. When a minor or moderate fault occurs in the main transformer, the online monitoring device first performs rapid detection and analysis using the palladium alloy thin-film hydrogen sensor and the membrane acetylene detector, and then performs corresponding full-component detection and analysis using the full-component monitoring device. The online monitoring device includes an oil-filled power main transformer body, transformer oil filled in the main transformer body, a micro frequency conversion circulating oil pump, a transformer oil flow sensor, a palladium alloy thin film hydrogen sensor device, a membrane acetylene detector device, a full component monitoring device, a micro frequency conversion oil-free air compressor device, a control module, a high-voltage circuit breaker on the main transformer power supply side, and connecting pipe fittings. The oil circuit of the online monitoring device includes the following structure: the lower part of the oil-filled power transformer body is equipped with a transformer oil outlet, which is connected to one side of the transformer oil outlet solenoid valve to control the transformer oil output and provide oil samples for the online monitoring device to perform detection; the upper part of the oil-filled power transformer body is equipped with a transformer oil inlet, which is connected to the transformer oil inlet valve to allow the return oil after detection by the online monitoring device to circulate back into the transformer; the other side of the transformer oil outlet solenoid valve is connected in sequence through a pipeline to the oil circuit of the micro frequency conversion circulating oil pump, the transformer oil flow sensor, the palladium alloy thin film hydrogen sensor device, the membrane acetylene detector device, and the oil inlet valve at the upper part of the oil-filled power transformer body, and the return flow is back into the transformer. The online monitoring device's gas path structure includes a miniature variable frequency oil-free air compressor and a gas path section of a membrane acetylene detector. When the gas path section of the membrane acetylene detector is working, the characteristic gas permeating from the ceramic diaphragm is carried by dry compressed air as a carrier gas to form a mixed gas, which is then discharged after passing through the gas path section of the membrane acetylene detector and the full component monitoring device in sequence. When the miniature variable frequency oil-free air compressor is working, it outputs a stable flow rate of dry oil-free air as a carrier gas into the ceramic diaphragm cavity. The air carries the characteristic gas and is discharged after passing through the gas path section of the membrane acetylene detector and the full component monitoring device in sequence. The palladium alloy thin-film hydrogen sensor device includes a sensor chip and a transmitter. The sensor chip is located in the center of the pipe behind the transformer oil flow sensor at the output end of the micro frequency conversion circulating oil pump. It directly measures the hydrogen content in the transformer oil flowing through the pipe. The transmitter is installed outside the pipe and is used to transmit the measurement data of the sensor chip to the control module. The membrane-type acetylene detector device includes a characteristic gas permeation membrane tube assembly and an acetylene detector. The characteristic gas permeation membrane tube assembly includes a characteristic gas permeation annular tube formed by an outer ring tube and an inner ring tube. The outer ring tube has a stainless steel shell, and the inner ring tube is a ceramic diaphragm with a highly permeable Teflon polymer composite membrane, which has the function of selectively permeating characteristic gas components. When transformer oil flows through the inner ring tube, it forms a sealed space between the inner ring tube and the outer ring tube for permeating fault characteristic gases. The characteristic gas permeation annular pipe is equipped with flanges at both ends, which connect it to other pipelines. A first small tube is installed at one end of the outer ring wall of the characteristic gas permeation annular tube; A second tube is installed at the other end of the outer ring wall of the characteristic gas permeation annular tube. One end of the second tube is inserted into the space between the inner and outer ring tubes, and the other end of the second tube is connected in sequence to an acetylene detector and a full component monitoring device. One end of the characteristic gas permeation annular pipe is connected to the output pipe of the micro frequency conversion circulating oil pump via the oil circuit section of the membrane acetylene detector device, and the other end of the characteristic gas permeation annular pipe is connected to the main transformer inlet valve on the upper part of the main transformer.

2. The step-type online monitoring device for dissolved gases in main transformer oil according to claim 1, characterized in that: The micro variable frequency oil-free air compressor device includes: a micro variable frequency air compressor, an adsorption column, an air tank, a pressure and flow stabilizing valve, and an air flow sensor; The outlet of the miniature variable frequency air compressor is connected in sequence via a pipeline to an adsorption column, an air storage tank, a pressure and flow stabilizing valve, and the first small tube of the outer ring of the characteristic gas permeation annular pipe. The adsorption column is filled with packing material that can adsorb moisture and impurities in the air. An electric contact pressure gauge is installed on the air storage tank to control the start and stop of the variable frequency oil-free air compressor within a certain pressure range. The compressed air output from the miniature variable frequency oil-free air compressor is regulated by the pressure and flow stabilizing valve to form a dry oil-free airflow with the required pressure and flow rate, which is supplied to the subsequent monitoring device as carrier gas. The air flow sensor transmits the flow data to the control module in real time, and the control module automatically adjusts the pressure and flow stabilizing valve.

3. The step-type online monitoring device for dissolved gases in main transformer oil according to claim 2, characterized in that: The full-component monitoring device is an online spectral monitoring device or an online chromatographic monitoring device.

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