Sulfur hexafluoride (SF6) gas is widely used in electrical equipment due to its stable chemical properties, excellent insulation capabilities, strong arc-quenching performance, and efficient cooling characteristics. Adhering to SF6 management regulations and the guidelines of the "pre-regulation," several key steps must be followed to ensure safe and effective operation of SF6-based systems.
First, after installation of SF6 electrical equipment, it is essential to re-examine the humidity and air content within the SF6 gas chamber, as well as perform a leak test before commissioning, ideally 24 hours after gas inflation. Once the equipment is energized, SF6 humidity tests and leak detection should be conducted every three months initially, with periodic checks every 1–3 years once the system stabilizes. If any significant changes in gas quality are detected, the “SF6 Testing Center†should be notified for further analysis.
For SF6 electrical equipment operating at pressures below 0.35 MPa or with low gas consumption—such as circuit breakers rated below 35kV—leak detection is only required if there are signs of abnormal conditions. If no leaks are found during testing and the initial humidity levels are acceptable, no further humidity monitoring is needed during normal operation.
This section outlines the methods used for testing gas humidity and detecting equipment leaks. The first method involves measuring the moisture content in the SF6 gas, which is crucial for preventing corrosion and ensuring proper insulation. Moisture in SF6 can lead to surface flashovers and damage to internal components, making it necessary to keep the gas as dry as possible. According to the pre-regulation, specific humidity limits apply depending on the operational state of the equipment.
The electrolysis method is commonly used to measure SF6 gas humidity. This technique involves passing the gas through an electrolytic cell where moisture is absorbed and decomposed. The amount of water present is determined by the current generated during electrolysis. A formula is applied to calculate the moisture content based on the current, pressure, temperature, and flow rate of the gas. Domestic moisture meters use this principle, and users should follow certain precautions, such as checking the gas pressure before testing, waiting 24 hours after charging, avoiding measurements on rainy days, and ensuring the system is properly dried before sampling.
Next, the gas leakage rate test, or leak detection, is divided into qualitative and quantitative methods. Qualitative detection involves identifying the location of a leak, while quantitative methods determine the exact leakage rate using techniques like the bandaging method or pressure drop algorithm. In the bandaging method, the equipment’s joints are sealed with plastic film, and the concentration of SF6 inside the sealed area is measured over time to estimate annual leakage. The pressure drop method tracks changes in pressure and temperature to assess gas loss over time.
Finally, SF6 gas composition analysis is performed after maintenance or when needed to identify potential issues. Key parameters include acidity, carbon tetrafluoride content, air content, decomposable fluorides, mineral oil levels, and overall purity. These values must meet specified standards to ensure safe and reliable operation.
Additionally, the density relay, a critical component in SF6 equipment, is tested to verify its correct functioning. It monitors the pressure of the gas and triggers alarms or locks the system when deviations occur. On-site testing procedures involve filling the system with SF6 gas, adjusting pressure, and comparing the results against standard values. If discrepancies are found, the relay should be sent to the manufacturer for inspection and adjustment.
By following these protocols, the integrity and safety of SF6 electrical equipment can be maintained, ensuring long-term reliability and performance.
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