SF6 gas, due to its excellent insulation and arc-extinguishing properties, is widely used in power systems. However, during the installation, maintenance, and repair of electrical equipment, operations such as gas recovery, storage, charging, and discharging are necessary to ensure the normal operation of the equipment and environmental safety. The SF6 gas recovery device, as the key equipment for these operations, requires correct on-site usage methods and strict adherence to precautions. It not only affects the service life and performance of the equipment, but also relates to the safety of the operators and environmental protection.

I. Preparations before operation
(1) Safety inspection
Grounding check: Ensure that the SF6 gas recovery device is well grounded, and the grounding resistance should comply with relevant standards. Use a grounding resistance tester to measure, generally requiring the grounding resistance to be no more than 4Ω. Good grounding can effectively prevent the risk of electric shock to the operators when the equipment leaks, and also protect the equipment from the influence of static electricity and other factors.
Pipeline inspection: Carefully inspect all pipeline connection parts of the device, checking for any signs of looseness, damage or leakage. You can use the method of applying soap water to inspect the pipeline connection points. If bubbles appear, it indicates that there is a leakage, and it is necessary to tighten or replace the pipeline in time. For aged or cracked pipelines, they must be replaced to ensure the safety and sealing of gas transmission.
Power supply check: Confirm that the power supply connected to the device is stable, with a voltage fluctuation range within the allowable working voltage range of the device. Generally, the device uses a three-phase four-wire system, 3 – 380V, 50Hz power supply. The normal operating power voltage is between 342 – 418V, with a deviation of 380 ± 10%. Use a multimeter to measure the power voltage to ensure it meets the requirements. At the same time, check if the power plug, socket, and power cord are damaged. If there are problems, repair or replace them in time to prevent equipment damage or safety accidents caused by power failures.
(2) Connecting pipelines
Select suitable pipelines: Use pressure-resistant hoses to connect the recovery device to the gas chamber interface of the power equipment. The pressure resistance level of the hose should meet the requirements of the SF6 gas working pressure, generally needing to be able to withstand at least 6MPa of pressure. At the same time, select appropriate length and diameter of hoses according to the actual usage scenario, while trying to shorten the pipeline length to reduce gas flow resistance and loss.
Ensure a sealed connection: When connecting the pipeline, install appropriate sealing rings at the interface to ensure a good seal. For threaded interfaces, tighten them according to the specified torque to prevent gas leakage due to poor sealing. After connection, recheck all connection parts to ensure there is no looseness.
(3) Pre-treatment (for contaminated gas)
If the SF6 gas to be recovered may be severely contaminated due to arc decomposition, it is necessary to detect the type of impurities before recovery. Use a professional gas component analyzer to sample and analyze the gas, determining whether it contains acidic decomposition substances such as SO2, HF, and other solid impurities. Based on the test results, select appropriate purification treatment methods, such as adding filtration steps or using targeted adsorbents, to ensure the normal operation of the recovery device and the quality of the recovered gas.
II. On-site operation procedures
(1) Recovering gas
Start the compressor: Turn on the compressor of the recovery device to draw the SF6 gas in the power equipment to the recovery device. Before starting the compressor, check if the oil level of the lubricating oil is within the normal range, generally located at 1/2 – 2/3 of the oil sight glass. After starting, observe the operating status of the compressor, including sound and vibration, to ensure normal operation. Monitoring pressure: Keep a close watch on the pressure gauges of the power equipment (source equipment), as the pressure inside the equipment gradually decreases as the gas is recovered. When the pressure approaches zero, stop the recovery operation to prevent air from mixing into the recovery device. Generally, when the pressure of the source equipment drops below 50 kPa (gauge pressure), it can be considered that the recovery is basically complete. At the same time, observe the relevant pressure gauges on the recovery device, such as the pressure gauge at the compressor inlet, to ensure that the pressure is within the normal working range. Generally, the pressure indicated by the M2 pressure gauge at the compressor inlet is 0.1 – 0.2 MPa.
(II) Purification treatment
Filtering impurities: The recovered SF6 gas passes through the molecular sieve in the device. The molecular sieve can effectively remove moisture from the gas. Generally, the molecular sieve’s adsorption capacity for moisture can reach 15% – 20% of its own weight. The gas will also pass through a alkaline filter to remove acidic decomposition products and other impurities generated by the arc decomposition, ensuring the purity of the gas.
Testing purity: Use an SF6 purity analyzer to test the purity of the purified gas to ensure it meets the relevant standards. According to the IEC 60480 standard, the purity of the recovered and purified SF6 gas should be no less than 99.8%. If the purity does not meet the requirements, the gas needs to be re-purified or the cause analyzed, and corresponding measures should be taken to solve the problem.
(III) Storage / Filling
Liquid storage: The purified SF6 gas is compressed and cooled to become liquid and stored in the storage container of the recovery device. During storage, pay attention to observing the liquid level of the storage container. The higher liquid level should not exceed 2/3 of the sight glass to prevent liquid overflow. At the same time, monitor the pressure inside the storage container to ensure it is within the safe range. The design pressure of the storage container is generally 1.5 – 2.5 MPa.
Filling equipment: When it is necessary to fill SF6 gas into the power equipment, the liquid SF6 gas is vaporized through the vaporizer in the device. According to the rated pressure requirements of the power equipment, slowly fill the gas, and observe the pressure gauge on the equipment until the required working pressure is reached. During the filling process, strictly control the filling speed to avoid rapid pressure increase that may cause damage to the equipment. The filling speed should not exceed 0.1 MPa/min.
(IV) Vacuum extraction
Equipment connection: Use a hose to connect the vacuum pump of the recovery device to the power equipment to ensure a good connection. Before connection, check the oil level of the vacuum pump and the tightness of the belt, etc., to ensure the vacuum pump is in good working condition.
Vacuum extraction operation: Start the vacuum pump and evacuate the power equipment to below 133 Pa. Generally, the vacuum degree can be monitored by a vacuum gauge. Maintain this vacuum degree for more than 30 minutes to ensure there are no residual gases inside the equipment. During the vacuum extraction process, if the vacuum degree cannot reach the required level or there is a significant increase, check whether there are leaks in the equipment and pipelines and handle them in time.
(V) Completion operation
Closing valves: After completing all operations, first close the valve between the recovery device and the power equipment, and then close all valves inside the device in sequence to ensure that the gas in the system is completely sealed. When closing the valves, operate in the prescribed sequence to avoid abnormal pressure or gas leakage due to improper operation.
Removing pipelines: Carefully remove the pipelines connecting the recovery device and the power equipment. During the removal process, be careful to prevent the leakage of residual gas in the pipelines. After removal, properly store the pipelines for future use.
Recording data: Record the amount of recovered gas, purity, and various data during the treatment process, such as the operating time of the compressor, the vacuum pump’s vacuum extraction time, the components and purity of the gas before and after purification. These data are of great significance for the subsequent maintenance of the equipment, performance evaluation, and gas management.