Electrical equipment installation site detection test system based on nitrogen and methane mixed leak detection gas

Abstract

The present invention relates to an on-site detection test system for electrical equipment installation based on a nitrogen and methane mixed gas as a leak detection gas, comprising a vacuum box (1), a gas detection subsystem placed therein, and a gas supply subsystem placed outside the vacuum box; the gas supply subsystem comprises a methane storage tank (51), a nitrogen storage tank (52), and a mixed gas storage tank (5); the methane storage tank (51) and the nitrogen storage tank (52) are connected in parallel to the mixed gas storage tank (5); the gas detection subsystem comprises a laser methane sensor (14), a photoacoustic spectrometer, and an ultrasonic imager (23), and can realize multi-dimensional monitoring of the type, leak point, and leak amount of gas leaked from the equipment. Compared with the existing technology, the present invention has the advantages of safety, high efficiency, and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical equipment installation detection, in particular to an electrical equipment installation on-site detection test system based on nitrogen and methane mixed leak detection gas. Background Art

[0002] In the field of electrical equipment installation, ensuring equipment sealing is critical for safe and stable operation. According to current national standards such as the "Standard for Acceptance Tests of Electrical Equipment for Electrical Installation Engineering," electrical equipment such as gas-insulated metal-enclosed switchgear (GIS) and generators have stringent sealing requirements. For example, the annual leakage rate of each independent gas chamber in GIS equipment must be controlled to no more than 0.5%. This indicator is determined by measuring the amount of SF6 gas leakage. The sealing performance of generators is directly related to insulation performance, operational reliability, and the stability of power supply. Once a gas leak occurs in electrical equipment, insulation performance deteriorates, potentially leading to serious accidents such as short circuits, fires, and even explosions. These accidents not only cause significant economic losses but also endanger personnel safety and the normal operation of the power grid. Therefore, timely leak detection at the electrical equipment installation site is essential. This can identify and resolve potential leaks before the equipment is put into operation, effectively reducing subsequent maintenance costs and safety risks.

[0003] Currently, commonly used leak detection methods primarily include helium and hydrogen leak detection technologies. However, leak detection at electrical equipment installation sites currently faces numerous challenges. Among traditional leak detection gases, helium leak detection technology is widely used due to its high sensitivity and excellent detection results. As an inert gas, helium has a small molecular weight and stable chemical properties, allowing it to penetrate tiny leaks and facilitate detection. However, helium resources are scarce, expensive, and difficult to recover, which severely limits its application in large-scale electrical equipment installation site inspections. Hydrogen, on the other hand, is flammable and explosive, requiring extremely strict safety precautions when used, which greatly limits its application in complex installation sites. Furthermore, existing detection equipment is generally complex to operate, requiring specialized technicians to operate and maintain. Furthermore, the equipment is bulky and difficult to carry, making it difficult to flexibly deploy and use at different installation sites, significantly hindering the smooth implementation of on-site inspections.

[0004] In order to reduce the cost of leak detection, some technical solutions use a mixture of hydrogen and nitrogen as the leak detection medium.

[0005] Chinese patent document CN109323822A discloses a method for testing the sealing performance of sealants. This method first fills a sealed box with compressed air at 0.6 atmospheres of pressure, maintains the pressure for two minutes, and observes whether the pressure gauge display value changes. If the pressure display value decreases, it indicates that the sealed box has a leak. Then, soapy water is poured on the seal to observe whether bubbles are generated. The leak point is then found. This method is only suitable for rough leak detection of test pieces. For extremely minor leaks, the bubbles generated are not obvious and cannot be detected. Therefore, the application of this method is limited.

[0006] Chinese patent publication CN111141462A discloses a gas leak detection method and device for a switchgear. This method first fills the switchgear's inflation chamber with C4F7N gas, maintains the pressure, and observes whether the pressure gauge display changes. If the pressure reading decreases, it indicates a leak in the sealed box. A C4F7N gas detector is then used to locate the C4F7N gas leak point. The C4F7N gas used as the tracer gas in this method has a molecular weight of 195 and a molecular diameter of approximately 0.56 nanometers. This method can only be used to detect leaks under specific operating conditions where the molecular diameter of the gas filling the switchgear is larger than that of the gas itself. It also cannot detect extremely minor leaks.

[0007] Chinese patent publication CN110146232B discloses a vacuum chamber hydrogen leak detection system. The system comprises a vacuum chamber system, a hydrogen-nitrogen mixing system, a hydrogen leak detection system, and an inflation system. By using a hydrogen-nitrogen mixture instead of helium for leak detection, the system effectively reduces detection costs. However, hydrogen is flammable and explosive, requiring strict safety precautions during use. This increases operational difficulty and safety risks, particularly at complex electrical equipment installation sites, where safety hazards are particularly prominent.

[0008] Separately, Chinese patent publication CN112539335A describes a helium-nitrogen mixed gas evacuation and refill recovery machine. This device can recycle and reuse the helium-nitrogen mixture, improving gas utilization. However, this system primarily focuses on helium recovery and fails to address the high cost of helium itself. Furthermore, the equipment is complex and requires high maintenance and operation.

[0009] Chinese patent publication CN112240820A discloses a gas tank leak detection and replenishment device that uses a mixture of SF6 and helium for leak detection and automatically replenishes the gas upon detection. However, the device is primarily designed for a specific type of gas tank, limiting its applicability and still relying on expensive helium as the detection medium.

[0010] Chinese patent publication CN103913279A describes a method and apparatus for testing the leak tightness of oil coolers using a helium-air mixture. This method reduces the use of pure helium by using the mixed gas. However, this method still uses helium as the primary test gas, failing to fundamentally address the high testing costs.

[0011] In summary, existing on-site leak detection technology for electrical equipment installations has the following problems: First, among traditional leak detection gases, helium has good leak detection effects but is extremely expensive, making it unsuitable for large-scale on-site detection projects. Second, although hydrogen is relatively low-cost, it is flammable and explosive, requiring strict safety precautions when used, limiting its application in complex installation sites. Third, existing detection equipment is complex to operate and requires professional technicians to operate and maintain. Fourth, the equipment is bulky and inconvenient to carry, making it difficult to flexibly deploy and use at different installation sites. Therefore, there is an urgent need to develop a low-cost, highly safe, easy-to-operate, and portable on-site detection test system for electrical equipment installations. Summary of the Invention

[0012] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide an electrical equipment installation on-site detection test system based on a mixture of nitrogen and methane leak detection gas, solve the problems of high cost and inconvenient operation of existing electrical equipment installation on-site detection, realize efficient, accurate and safe on-site leak detection, and ensure the installation quality and operation safety of electrical equipment.

[0013] The objectives of the present invention can be achieved through the following technical solutions: providing an electrical equipment installation on-site detection test system based on a nitrogen and methane mixed leak detection gas, comprising a vacuum box, a gas supply and recovery subsystem, and a gas detection subsystem; the gas supply and recovery subsystem comprises a methane storage tank, a nitrogen storage tank, and a mixed gas storage tank, the methane storage tank and the nitrogen storage tank being connected in parallel to the mixed gas storage tank, which is connected to the vacuum box; the gas detection subsystem comprises a laser methane sensor, a photoacoustic spectrometer, and an ultrasonic imager; the workpiece to be inspected is placed in the vacuum box, the mixed gas storage tank inputs a nitrogen and methane mixed gas into the vacuum box as a leak detection gas, the methane concentration in the vacuum box is detected by the laser methane sensor, and when the methane concentration in the mixed gas exceeds a set threshold, an alarm signal is issued and relevant information is recorded. Simultaneously, the photoacoustic spectrometer and the ultrasonic imager scan the workpiece to be inspected to find the leak point and mark the leak point on the workpiece to be inspected.

[0014] A further preferred embodiment of the present invention is that methane gas in the mixed gas storage tank accounts for 4.5-9.5% of the total volume of the mixed gas.

[0015] A further preferred embodiment of the present invention is that the vacuum box is connected to a vacuum pump group, and the vacuum pump group includes a screw vacuum pump and a Roots vacuum pump connected in series.

[0016] A further preferred embodiment of the present invention is that a compressor and a vacuum pump are provided in parallel on the connecting pipe between the mixed gas storage tank and the vacuum box.

[0017] A further preferred solution of the present invention is that the vacuum box is further connected to a pressure sensor and a negative pressure sensor.

[0018] A further preferred embodiment of the present invention is that the system further comprises a purification device, which filters the mixed gas exhausted from the workpiece to be inspected, and recovers the filtered nitrogen and methane for reuse.

[0019] A further preferred embodiment of the present invention is as follows: the laser methane sensor is connected to a data processor, which analyzes and processes the data collected by the laser methane sensor. Simultaneously, a photoacoustic spectrometer and an ultrasonic imager scan the workpiece to be inspected for leaks. The photoacoustic spectrometer and ultrasonic imager are connected to a computer via a data acquisition card, which analyzes and processes the data collected by the laser methane sensor, the photoacoustic spectrometer, and the ultrasonic imager. The leak point is then marked on the modeled workpiece to be inspected. The detection process using a high-precision laser methane sensor combined with photoacoustic spectrometer positioning and ultrasonic imager is as follows:

[0020] Initial screening: The laser methane sensor quickly scans the surface of the equipment or the gas cavity to identify areas of abnormal methane concentration. The laser methane sensor is a commercially available laser methane sensor with ppm-level detection capability.

[0021] Precise Positioning: Ultrasonic imaging scans the abnormal area, while photoacoustic spectroscopy distinguishes different molecules. By overlaying acoustic field images with visible light (using augmented reality technology), the localized gas leak point is visualized. Data Linkage: Methane concentration trends are simultaneously analyzed with ultrasonic intensity and frequency characteristics (such as PRPD patterns) to assist in determining the leak size and gas type.

[0022] By combining high-precision laser methane sensors with photoacoustic spectroscopy positioning and ultrasonic imaging, the technical advantages are as follows: Non-contact detection: supports live detection to avoid equipment downtime losses (such as GIS equipment detection efficiency increased by more than 60%).

[0023] Early warning capability: The methane detection sensitivity is two orders of magnitude higher than that of traditional catalytic combustion sensors, and ultrasonic imaging can detect micron-level leakage gaps.

[0024] Quantitative assessment: Methane concentration data is combined with ultrasonic intensity and frequency domain characteristics to provide a quantitative rating basis for equipment status (such as the fault gas concentration classification in the IEEE C57.104 standard).

[0025] A further preferred embodiment of the present invention is that the vacuum box is made of high-strength stainless steel with good sealing performance, and the bottom of the box is directly used as a testing platform for placing electrical equipment components to be tested; an integrated operation panel is provided on the side of the box.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. By using a mixture of nitrogen and methane instead of traditional helium as the leak detection gas, the detection cost is significantly reduced. At the same time, the stability of nitrogen is effectively reduced to reduce the explosion risk of methane, solving the problems of high cost of traditional helium leak detection and flammable and explosive hydrogen.

[0028] 2. By combining high-precision laser methane sensors with photoacoustic spectroscopy and ultrasonic imaging, it is possible to accurately detect tiny leaks during the installation of electrical equipment and pinpoint the leak points, greatly improving detection accuracy and reliability and increasing the efficiency of gas-based equipment leak detection.

[0029] 3. The system is designed with an integrated operation panel, which makes the detection process more convenient and eliminates the need for professional technicians to operate and maintain it, thus solving the problem of complex operation of existing detection equipment.

[0030] 4. The vacuum box is made of high-strength stainless steel with a compact structure, easy to carry and can be flexibly deployed and used at different installation sites, solving the problem of bulky and inconvenient carrying of existing equipment.

[0031] 5. The setting of ventilation and purification system ensures the safety and environmental protection of the testing process. The purified gas can be recycled and reused, which meets the requirements of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Install a structural diagram of the on-site detection test system for electrical equipment based on a nitrogen and methane mixed leak detection gas;

[0033] Figure 2 Installation layout of on-site detection test system for electrical equipment based on nitrogen and methane mixed leak detection gas;

[0034] Figure 3 Workflow diagram for the on-site detection test system installed for electrical equipment based on a mixture of nitrogen and methane leak detection gas. DETAILED DESCRIPTION

[0035] The technical solutions of the present invention will be described clearly and completely below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0036] Methane has a relative molecular mass of 16 and a small molecular diameter of only approximately 0.4 nm. This allows it to easily penetrate leak channels such as cracks and welds, enabling detection of even the smallest leaks. While slightly heavier than helium and hydrogen, methane has a lower average molecular mass than air, which is 29 nm. This allows it to diffuse rapidly through air, making it an effective leak detection gas. Furthermore, methane is widely present in nature and relatively inexpensive to obtain, creating opportunities for reducing detection costs. Generally, methane concentrations of 5% to 15% by volume in air can explode when exposed to ignition, making it unsuitable for use as a leak detection gas alone. However, mixing methane with chemically stable nitrogen can reduce the explosion risk to a certain extent, enabling its leak detection capabilities to be performed safely and within controllable limits. This provides a new approach to addressing the current challenges faced by on-site electrical equipment installation inspections.

[0037] To address the high costs, complex operations, and lack of portability associated with existing on-site testing technologies for electrical equipment, the present invention proposes an on-site testing system for electrical equipment installations based on a nitrogen and methane mixture leak detection gas. By rationally utilizing the properties of nitrogen and methane, low-cost, safe, and efficient on-site testing is achieved. Unless otherwise specified, the components or equipment described herein are commercially available in the art. For example, the laser methane sensor 14 used in the present embodiment utilizes the commercially available IGARO LMD-A laser methane sensor, which features high sensitivity (ppm-level detection capability) and strong anti-interference capabilities.

[0038] The photoacoustic spectroscopy positioning and ultrasound imaging device are commercially available photoacoustic spectroscopy positioning device (FUJIFILM Visual Sonics Vevo LAZR is used in the following examples) and commercially available ultrasound imaging device (Philips EPIQ Elite ultrasound system is used in the following examples). Example 1

[0039] like Figures 1 and 2 As shown, an electrical equipment installation on-site detection test system based on nitrogen and methane mixed leak detection gas includes a vacuum box 1 and a gas supply and recovery subsystem and a gas detection subsystem placed therein;

[0040] Among them, the vacuum box 1 is a sealed box structure made of high-strength stainless steel. Its inner surface is polished and cleaned after processing to ensure a good background and very little gas accumulation, improve the pumping speed of the vacuum box, have good sealing performance, and can withstand the internal negative pressure environment. The bottom of the vacuum box 1 is designed to be a flat structure, which is directly used as a detection platform for placing the workpiece 15 to be detected. The vacuum box 1 is provided with a quick connector and a flexible hose for connecting with the workpiece 15 to be detected. The flexible hose connection is convenient and fast, greatly improving the operating efficiency. The side of the vacuum box 1 is provided with an openable sealed door to facilitate the placement and removal of the workpiece 15 to be detected. The vacuum box 1 is also connected to a pressure sensor 17 and a negative pressure sensor 18. The pressure sensor 17 is used to monitor the pressure inside the vacuum box as a survival measure to prevent the pressure inside the vacuum box from abnormally increasing and causing damage to the equipment. The negative pressure sensor 18 is used to measure the negative pressure value inside the vacuum box. After reaching the set negative pressure value, the system vacuuming work stops. The vacuum chamber 1 is connected to a vacuum pump assembly comprising a screw vacuum pump 10 and a Roots vacuum pump 11 connected in series. The Roots vacuum pumps 11 and 10 in the system are designed to quickly evacuate the chamber 1, shortening the time required for a single test. This combination of a screw vacuum pump and a Roots vacuum pump provides faster pumping speeds under high vacuum conditions, saving time during leak detection testing.

[0041] The gas supply and recovery subsystem includes a methane storage tank 51, a nitrogen storage tank 52, and a mixed gas storage tank 5. The methane storage tank 51 is a high-pressure gas storage container that stores high-purity methane gas. It is equipped with a pressure gauge and a safety valve for monitoring and controlling the gas pressure within the tank. The outlet of the methane storage tank 51 is connected to the mixed gas storage tank 5 via a pipeline, equipped with a solenoid valve V8 for precisely controlling the flow of methane gas. The nitrogen storage tank 52 is a high-pressure gas storage container that stores high-purity nitrogen gas. It is also equipped with a pressure gauge and a safety valve. The outlet of the nitrogen storage tank 52 is connected to the mixed gas storage tank 5 via a pipeline, equipped with a solenoid valve V9 for precisely controlling the flow of nitrogen gas. The mixed gas storage tank 5 is a medium-sized gas storage container used to mix and store a mixture of methane and nitrogen. A stirring device is installed within the mixed gas storage tank 5 to ensure that the methane and nitrogen gases are thoroughly mixed. The gas outlet of the mixed gas storage tank 5 is connected to the vacuum box 1 through a pipeline, and the compressor 3 and the vacuum pump 16 are connected in parallel on the connecting pipeline. The compressor 3 transports the methane and nitrogen mixed gas in the mixed gas storage tank 5 to the workpiece 15 to be tested. At the end of the test, the vacuum pump 16 is used to pump the methane and nitrogen mixed gas in the workpiece back into the mixed gas storage tank 5 to recycle the mixed gas.

[0042] Each connecting pipeline is provided with a solenoid valve, among which the solenoid valve V8 is used to control the amount of methane input into the mixed gas storage tank 5, and the solenoid valve V9 is used to control the amount of nitrogen input into the mixed gas storage tank 5. There is a solenoid valve V5 on the connecting pipeline between the mixed gas storage tank 5 and the compressor 3, and the solenoid valve V5 is used to control the amount of mixed gas entering the compressor 3. A solenoid valve V7 is provided on the pipeline between the mixed gas storage tank 5 and the vacuum pump 16, and the solenoid valve V7 is used to control the amount of mixed gas in the workpiece after the test is recovered by the vacuum pump 16 and enter the mixed gas storage tank 5; the vacuum box 1 is provided with a total input pipeline 12 for gas entry, the compressor 3 and the vacuum pump 16 are respectively connected to the total input pipeline 12 through pipelines, and solenoid valves V4 and solenoid valves V6 are respectively provided on the connecting pipeline, and a purification device 22 is also provided on the pipeline between the solenoid valve V6 and the vacuum pump 16, which is used to filter the mixed gas discharged from the workpiece to be tested, and the filtered nitrogen and methane are recycled. The total input pipeline 12 is also connected to the negative pressure sensor 19 through the solenoid valve V14, connected to the pressure sensor 20 through the solenoid valve V13, and connected to the blower through the solenoid valve V3. The total input pipeline 12 is connected to the quick connector in the vacuum box 1, and is connected to the workpiece to be inspected 15 using the quick connector.

[0043] A solenoid valve V2 is provided on the pipeline connecting the screw vacuum pump 10 and the Roots vacuum pump 11 to the vacuum box 1. The screw vacuum pump 10, the Roots vacuum pump 11 and the solenoid valve V2 are used to quickly remove methane gas leaked into the vacuum box due to leakage of the workpiece, so as to prepare for subsequent workpiece leak detection and save test time. Because the methane gas leaked from the workpiece into the vacuum box 1 is very small, it can be discharged into the atmosphere by opening the screw vacuum pump 10, the Roots vacuum pump 11 and the solenoid valve V2.

[0044] When delivering a mixed gas of methane and nitrogen into the workpiece 15 to be inspected, the solenoid valves V3, V6 and V14 are closed, and the solenoid valves V4, V5 and V13 are opened at the same time; when recovering a mixed gas of methane and nitrogen from the workpiece, the solenoid valves V3, V4 and V13 are closed, and the solenoid valves V6, V7 and V14 are opened at the same time; the pressure sensor 20 is used to monitor the pressure inside the workpiece as a protective measure to prevent the abnormal increase in the pressure inside the workpiece from causing damage to the equipment; the negative pressure sensor 19 is used to measure the negative pressure value inside the workpiece. When the set negative pressure value is reached, the system mixed gas recovery work stops.

[0045] The gas detection subsystem includes a laser methane sensor 14, a photoacoustic spectrometer, and an ultrasonic imager 23. The methane concentration measurement device utilizes the laser methane sensor 14, making measurement and control more precise, stable, and reliable. The laser methane sensor 14, the photoacoustic spectrometer, and the ultrasonic imager 23 are installed inside the vacuum chamber 1. The laser methane sensor 14 monitors the methane concentration inside the chamber in real time. The photoacoustic spectrometer and the ultrasonic imager 23 scan the workpiece to detect leaks. The computer system marks the leak points on the scanned image of the workpiece.

[0046] Laser methane sensor 14 utilizes laser absorption spectroscopy technology, offering high sensitivity and rapid response, enabling accurate detection of low-concentration methane gas. Laser methane sensor 14 is connected via a data cable to the system control unit (in this embodiment, a computer control system is employed, housed within electrical control box 6 and including a human-machine interface (i.e., display screen) connected to the controller, which is mounted on the front panel of electrical control box 6). This transmits detection data in real time to the control unit for analysis and processing.

[0047] The system also includes a ventilation device, which uses a high-efficiency fan, such as Figure 1 As shown, a high-efficiency blower is connected via solenoid valve V11 to discharge any trace methane gas that may exist in the box into the atmosphere after the test is completed.

[0048] In this embodiment, the entire system is concentrated in a 20-foot standard container 4. Figure 2 As shown, the vacuum box 1 is easily transported to the equipment installation site for testing. A partition 2 separates the vacuum box 1 from other equipment. The workpiece to be tested is pushed into or out of the vacuum box 1 using a tool trolley. Inside the vacuum box 1 are hose connectors and a laser methane sensor 14 for convenient connection to the workpiece to be tested. If the workpiece leaks, the methane gas inside is released into the vacuum box 1 and detected by the laser methane sensor 14.

[0049] The system is provided with a unit consisting of a screw vacuum pump 10 and a Roots vacuum pump 11, which are connected to the vacuum box 1 through a pipeline to evacuate the vacuum box 1. The compressor 3 and the vacuum pump 16 are connected in parallel to the main input pipeline 12, and the workpiece to be inspected in the vacuum box 1 is connected through the main input pipeline 12. The screw vacuum pump 10 and the Roots vacuum pump 11 are installed on a frame 9 in order from bottom to top.

[0050] The system also features a low-pressure methane and nitrogen mixed gas storage tank 5. Compressor 3 pumps the methane and nitrogen mixture from tank 5 into the workpiece under test. After testing, the methane and nitrogen mixture in the workpiece under test is pumped back into tank 5 via vacuum pump 16. Vacuum pump 16 is mounted on mounting bracket 8.

[0051] like Figure 3 As shown, the system working process is as follows:

[0052] S1. Place the workpiece 15 to be inspected into the vacuum box 1 and connect the workpiece interface pipe 21;

[0053] S2. Close the sealing door of the vacuum box 1 to ensure that the vacuum box 1 is well sealed; press the start button on the control panel of the electric control box 6 to start the workpiece gas leak detection process.

[0054] S3, the PLC electrical control program automatically opens the solenoid valve V2 and the solenoid valve V12, starts the screw vacuum pump 10 and the Roots vacuum pump 11, closes the solenoid valve V10 and the solenoid valve V11, and evacuates the vacuum box 1 to 100 Pa (absolute pressure), and maintains it for 5 minutes to detect whether there is any leakage in the vacuum box 1. During this period, the system automatically compares the negative pressure value collected by the negative pressure sensor 18. If the fluctuation value is no more than 10 Pa, the vacuum box 1 is judged to have passed the leak detection. Otherwise, it is unqualified and the vacuum box needs to be inspected and repaired. Simultaneously, the computer control program automatically opens solenoid valves V6 and V14, starts screw vacuum pump 16, and closes solenoid valves V3, V4, V7, and V13. The vacuum is then evacuated to 100 Pa (absolute pressure) on the workpiece 15 to maintain this pressure for 5 minutes to detect leaks. During this time, the system automatically compares the negative pressure values ​​collected by negative pressure sensor 19. If the fluctuation is no greater than 5 Pa, the workpiece 15 is deemed to have passed the gas leak test. Otherwise, it is deemed unqualified and the workpiece must be removed for manual processing, thus completing the leak test. It should be noted that the purpose of leak testing vacuum chamber 1 at this stage is to prepare for the next step, shorten testing time, and prevent leaks in the vacuum chamber. Methane from the workpiece could leak into the vacuum chamber and then into the atmosphere, causing the laser methane concentration detector installed in the chamber to measure low values ​​and distort the experimental results.

[0055] If the leak test is qualified in step S4, the process goes to step S5. If the leak test is unqualified, an alarm is sounded and the air inlet solenoid valve V3 of the vacuum box 1 is opened to break the vacuum of the vacuum box 1 and allow air to flow in. After 3 minutes, the vacuum box door is opened and the unqualified workpiece is taken out.

[0056] S5. Continue to evacuate the vacuum box 1 to 100 Pa and maintain it for 5 minutes. Perform methane detection on the vacuum box 1. When the detected methane concentration is less than the set value, it means that there is no residual methane gas in the vacuum box 1 and it will not interfere with the subsequent detection. The test is qualified and the process proceeds to step S6.

[0057] S6. After the test is completed, the solenoid valve V2, the screw vacuum pump 10, and the roots vacuum pump 11 are closed. The solenoid valves V4, V5, and V13, as well as the compressor 3, are opened. A nitrogen and methane mixed gas is fed from the mixed gas storage tank 5 into the workpiece to be tested 15. The methane gas in the mixed gas accounts for 4.5-9.5% of the total volume of the mixed gas. The laser methane sensor 14 monitors the methane concentration in the vacuum box 1 in real time.

[0058] S7. When the methane concentration in the mixed gas exceeds the set threshold, the system will issue an alarm signal and record relevant information, indicating that there is a leak point in the workpiece 15 to be tested, and the workpiece gas leak test is judged to be unqualified.

[0059] The photoacoustic spectroscopy positioning and ultrasonic imaging device 23 scans the workpiece to be inspected to find the leak point, and transmits the obtained data to the computer system, which displays the leak point.

[0060] S8, when it is detected that the methane concentration in the mixed gas does not exceed the set threshold, it is determined to be qualified, and the solenoid valve V5 and the solenoid valve V4 and the compressor 3 are closed, and the vacuum pump 16, the solenoid valve V6 and the solenoid valve V7 are opened to recover the methane and nitrogen mixed gas in the workpiece to the mixed gas storage tank 5;

[0061] S9. After the test is completed, open the solenoid valve V3 and the solenoid valve V11, close other valves, open the vacuum box door, and take out the workpiece.

[0062] In this embodiment, the workpiece to be tested is an SF6 switchgear as an example. The SF6 switchgear controls the leakage of SF6 gas during operation. Based on an annual leakage rate of 0.1% of SF6 gas, the set leakage rate alarm value in actual leak detection is obtained through the following steps:

[0063] 1. Convert the annual SF6 leakage rate of 0.1% volume leakage into gas leakage rate:

[0064] Assuming the workpiece volume is 300L and the SF6 filling pressure is 0.15Mpa (absolute pressure), the leakage rate corresponding to an annual volume leakage of 0.1% is:

[0065] 300×10 -3 × 0.15×10 6 ×0.1% / 3600×24×365

[0066] =1.4×10-6 Pa.m 3 / S

[0067] 2. For viscous flow, the leakage rate of different gases is inversely proportional to the viscosity coefficient of the gas, so 1.4×10 -6 Pa.m 3 / S corresponding to the methane leakage rate of SF6

[0068] Q = Q SF6 (η SF6 / η CH4 )

[0069] =1.4×10 -6 × (1.42 × 10 -5 / 1.12×10 -5 )

[0070] =1.78×10 -3 Pa.m 3 / S

[0071] Where, Q is the leakage rate of methane (Pa.m 3 / S)

[0072] Q SF6 - SF6 leakage rate when the test piece is working (Pa.m 3 / S)

[0073] η CH4 - Viscosity coefficient of methane (1.12×10 -5 Pa. S)

[0074] η SF6 - The viscosity coefficient of SF6 (1.42×10 -5 Pa.S)

[0075] 3. Setting of alarm leakage rate value

[0076] 1) Set the relevant parameters of the vacuum box (such as leak detection time, leak detection pressure, etc.);

[0077] Adjust the standard leak to the annual leakage rate value of 1.78×10 - 3 Pa.m 3 / S;

[0078] 2) Connect the standard leak to the vacuum box through a tee;

[0079] 3) Perform an empty vacuum box leak test and record the leak rate value Q0 at the end. This value is the background value of the vacuum box. If the background value Q0 exceeds the standard, the system will alarm.

[0080] 4) Open the standard leak hole, observe the leak rate value of the leak detector, and write down the leak rate value Q at the end B ;

[0081] 5) Set the alarm value of the vacuum box to the leak rate value Q of the standard leak hole B That's it.

[0082] The leakage rate of SF6 gas calculated above is 1.4×10 -6 Pa.m 3 Taking / S as an example, in order to measure obvious pressure changes, a long time is required. On the one hand, the test time is greatly prolonged, and on the other hand, more SF6 gas is leaked out, resulting in waste. Therefore, the method of observing pressure changes to measure the leakage of SF6 switchgear is not suitable. Using this solution can shorten the test time and improve test efficiency.

[0083] The present invention is particularly suitable for leak detection of gases with relatively small leakage rates, such as annual leakage rates of 0.1% to 10%. It is also applicable to leak detection of gases with relatively large leakage rates, such as annual leakage rates greater than 10%. In contrast, the method of observing pressure changes is not suitable for leak detection of gases with relatively small leakage rates, such as annual leakage rates of 0.1% to 10%. It takes several days or even months to observe obvious pressure changes, which is completely unacceptable.

Claims

1. An electrical equipment installation site detection test system based on a nitrogen and methane mixed leak detection gas, characterized by: It includes a vacuum box (1) and a gas detection subsystem and a gas supply and recovery subsystem; The gas supply and recovery subsystem includes a methane storage tank (51), a nitrogen storage tank (52), and a mixed gas storage tank (5), wherein the methane storage tank (51) and the nitrogen storage tank (52) are connected in parallel to the mixed gas storage tank (5); The gas detection subsystem includes a laser methane sensor (14), a photoacoustic spectrometer and an ultrasonic imager (23); The workpiece to be inspected (15) is placed in a vacuum box (1), and a mixed gas storage tank (5) inputs a mixed gas of nitrogen and methane into the vacuum box (1) as a leak detection gas. The methane concentration in the vacuum box (1) is detected by a laser methane sensor (14). When the methane concentration in the mixed gas exceeds a set threshold, an alarm signal is issued and relevant information is recorded. At the same time, a photoacoustic spectrometer and an ultrasonic imager (23) scan and find leak points on the workpiece to be inspected; The laser methane sensor (14) is a commercially available laser methane sensor with ppm-level detection capability; The photoacoustic spectrometer uses multi-wavelength laser excitation to detect the generated ultrasonic waves, achieving high-resolution photoacoustic imaging and distinguishing different molecules; The ultrasonic imager (23) uses sound wave reflection to form an image; The laser methane sensor (14), the photoacoustic spectrometer and the ultrasonic imager (23) work together to perform fixed-point visual leak detection on the workpiece (15) to be inspected and locate the leak point; The detection process using a high-precision laser methane sensor combined with photoacoustic spectroscopy positioning and ultrasonic imaging is as follows: Initial screening: The laser methane sensor quickly scans the equipment surface or gas cavity to identify areas of abnormal methane concentration. The laser methane sensor is a commercially available laser methane sensor with ppm-level detection capability. Precise positioning: The ultrasonic imager scans the abnormal area at a fixed point, and the photoacoustic spectrometer distinguishes different molecules. By superimposing the acoustic field image with visible light, the local gas leak point is visualized. Data linkage: The methane concentration trend is synchronously analyzed with the ultrasonic intensity and frequency characteristics to assist in determining the leak size and leaked gas type. The methane gas in the mixed gas storage tank (5) accounts for 4.5-9.5% of the total volume of the mixed gas.

2. The electrical equipment installation on-site detection test system based on nitrogen and methane mixed leak detection gas according to claim 1 is characterized in that: The vacuum box (1) is connected to a vacuum pump group, which includes a screw vacuum pump (10) and a Roots vacuum pump (11) connected in series.

3. The electrical equipment installation on-site detection test system based on nitrogen and methane mixed leak detection gas according to claim 1 is characterized in that: A compressor (3) and a vacuum pump (16) are provided in parallel on the connecting pipe between the mixed gas storage tank (5) and the vacuum box (1).

4. The electrical equipment installation on-site detection test system based on nitrogen and methane mixed leak detection gas according to claim 1 is characterized in that: The vacuum box (1) is also connected to a pressure sensor (17) and a negative pressure sensor (18).

5. The electrical equipment installation on-site detection test system based on nitrogen and methane mixed leak detection gas according to claim 1 is characterized in that: The system further comprises a purification device (22), which filters the mixed gas discharged from the workpiece to be inspected, and the filtered nitrogen and methane are recovered and reused.

6. The electrical equipment installation on-site detection test system based on nitrogen and methane mixed leak detection gas according to claim 1, characterized in that: The laser methane sensor (14), the photoacoustic spectrometer and the ultrasonic imager (23) are connected to a computer via a data acquisition card, and the computer analyzes and processes the data collected by the laser methane sensor (14), the photoacoustic spectrometer and the ultrasonic imager (23).

7. The electrical equipment installation on-site detection test system based on nitrogen and methane mixed leak detection gas according to claim 1 is characterized in that: Data analysis and processing is performed by a computer control system installed in an electric control box (6). The computer control system marks the leakage point on the scanned image of the workpiece to be detected.

8. The electrical equipment installation on-site detection test system based on nitrogen and methane mixed leak detection gas according to claim 1 is characterized in that: The vacuum box (1) is made of stainless steel with high strength and good sealing performance. The bottom of the box is directly used as a testing platform for placing the electrical equipment components to be tested; an integrated operation panel is provided on the side of the box.

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