1 Introduction With the rapid development of the construction and renovation of the "two networks", the usage of SF6 circuit breakers and GIS electrical appliances is increasing at a rate of about 15%. These products meet the requirements of oil-free operation, as well as miniaturization and automation. However, accidents can occur if they are used improperly. 2 Introduction to SF6 power equipment (1) SF6 circuit breaker. The insulation and arc-extinguishing medium of SF6 circuit breaker is SF6 gas. The advantages are as follows: ① Strong arc-extinguishing ability, high dielectric strength, good insulation performance, high breaking voltage, and safe and reliable use. ② The medium recovery speed is particularly fast, the cooling characteristics are good, the performance of breaking near-zone faults is particularly good, and the service life is long. ③ The SF6 gas arc decomposition field does not contain carbon or other substances that affect the insulation ability, and the contacts are burned very slightly in the breaking arc. Therefore, SF6 circuit breakers also have the advantages of a large number of breaking cycles, simple installation and operation, long maintenance cycle, and reliable operation. (2) GIS combined electrical appliances. GIS combined electrical appliances consist of circuit breakers, disconnect switches, grounding switches, transformers, surge arresters, busbars, connectors, and other units, all enclosed in a grounded metal body. The interior is filled with SF6 gas under pressure, which has excellent arc-extinguishing and insulation capabilities. Because GIS is both enclosed and combined, it occupies a small area and space, is largely unaffected by the external environment, does not generate noise or radio interference, operates safely and reliably, and requires minimal maintenance. Its outstanding advantages are: ① It minimizes the footprint and volume of the entire power distribution system, resulting in a very compact structure. This is especially important in densely populated metropolitan areas and dense load centers. ② The fully enclosed electrical structure is unaffected by various harsh natural conditions such as rain, lightning, dust, sand, and salt spray, reducing the possibility of equipment accidents, making it particularly suitable for industrial pollution, harsh climates, and high-altitude areas. ③ Installation is convenient. As GIS has developed towards three-phase common-tube, composite, and intelligent directions, it is generally composed of a whole or several units, which can greatly shorten the installation period. 3. Operation and Maintenance Practice of SF6 Power Equipment (1) Safe Operation of SF6 Power Equipment. At present, substations managed by power companies at 220kV and below are vigorously promoting unmanned operation mode based on the relatively mature "four remote" technology. Whether SF6 power equipment can operate safely and reliably depends on the quality of equipment manufacturing, installation, operation monitoring and maintenance. Operation practice has proven that the gas pressure of SF6 power equipment drops frequently, sometimes even below the alarm pressure. The drop in gas pressure indicates that some parts of the SF6 power equipment are leaking, which will inevitably reduce the insulation strength and arc extinguishing ability of SF6 gas, bringing serious hidden dangers to the safe operation of the equipment. Therefore, real-time and accurate monitoring of the pressure value of SF6 power equipment is very important. When the pressure drops or is frequently depressurized, the transmission of alarm signals should be timely and reliable. It should be able to intelligently display abnormal data to inform the operators to handle it. In operation, the humidity of SF6 power equipment should generally be monitored once every three months. Since the humidity increases with the rise in temperature, the monitoring of moisture content should be strengthened in summer, and units with the conditions should invest in pressure and moisture online detection systems. (2) Leak detection and humidity measurement of SF6 power equipment. Leak detection can be performed using both qualitative and quantitative methods. Qualitative measurements typically employ high-sensitivity probes to detect leak-prone areas specified by the equipment. Its advantages include audible and visual alarms and easy location. In the field, qualitative leak detection is more practical and includes: simplified qualitative leak detection, pressure drop method, segmented location method, and local accumulation method. The simplified qualitative method uses a general leak detector to check all assembled sealing surfaces, pipe connections, and other suspected areas. It is simple and can locate relatively obvious local leaks. The pressure drop method uses a precision pressure gauge to measure the SF6 gas pressure, repeating the measurement every few days or tens of days, and combining temperature conversion or lateral comparison to determine the pressure drop. The segmented location method is suitable for circuit breakers with three-phase SF6 gas connections. Dividing the SF6 gas system into several parts before leak detection reduces randomness. The local accumulation method involves wrapping the measurement area with plastic sheeting, and after several hours, using a leak detector to measure whether there is leaking SF6 gas inside the plastic sheeting. This is currently a commonly used qualitative leak detection method. Operational practice has shown that the main leakage points of SF6 circuit breakers are: various detection ports, welds, gas filling nozzles, flange connection surfaces, pressure gauge connection pipes, and sealing bases. Common leakage points of GIS include: welds, flange joint surfaces, gas filling nozzles, and pressure gauges. Quantitative measurement can be performed using the hanging bottle leak detection method and the local wrapping method, and should be carried out 24 hours after filling. The LDD2000 leak detector can be used as a quantitative measuring instrument, which is safe, convenient, and relatively ideal. The judgment standard for quantitative measurement is an annual leakage rate of no more than 1%. Humidity measurement: Humidity measurement should be carried out after the humidity in the gas chamber has stabilized, generally 24 hours after filling the enclosed combined electrical appliance. A dew point moisture meter or a DP19-SH-Ⅲ type SF6 moisture meter can be used for testing. The required values ​​for moisture content in SF6 gas (PPm, V/V) are shown in Table 1. [align=center]Table 1 Moisture Content Requirements[/align] When measuring the same equipment with different instruments, different data may be obtained. This may be related to the performance of the instrument itself, as well as the gas pipeline and operation. It is recommended to use the same instrument to measure to maintain the comparability of the data. Before measuring the gas, the gas pipeline joints should be dried to avoid affecting the accuracy of the measurement. 4 Precautions for SF6 Power Equipment Maintenance SF6 gas is sealed in SF6 power equipment as an insulating and arc-extinguishing medium. Due to manufacturing quality and installation process, aging of sealing elements, leakage of SF6 equipment is unavoidable, and moisture infiltration also exists. Gas leakage and moisture infiltration are the key factors affecting the long-term safe operation of SF6 equipment and should be given high attention. (1) When gas needs to be replenished, the new SF6 gas should be accepted according to the new gas quality standard. The purity of the new SF6 gas should not be less than 99.8%, and the purity after filling the equipment should not be less than 97%. The eight technical indicators, including carbon tetrafluoride, air, moisture, purity, and acidity, should meet the national standards. Before inflation, all pipelines must be flushed clean, and after inflation, the pressure should be slightly higher than the required value. The moisture content should be tested by professionals using special instruments, and moisture should be prevented from seeping in during on-site testing. (2) When entering the gas chamber for work, the gas chamber should be fully ventilated beforehand. Work can only be carried out when the oxygen content in the gas chamber reaches 18% or more. (3) When reinstalling SF6 power equipment, the sealing groove surface should be clean and free of scratches. Sealing rings made of high-quality materials such as neoprene rubber with special formulas should be selected. Sealing (gasket) rings that have been used should not be reused. When applying sealant, it should not be allowed to flow into the inside of the sealing (gasket) ring and come into contact with SF6 gas. (4) When overhauling SF6 power equipment, firstly, the operators should strictly follow the work location and work on the designated equipment as specified on the work order; secondly, the overhaul process should be standardized. That is, the responsibilities of the operators, the strictness of the implementation of rules and regulations, technical standards and process standards should be specifically stipulated and quantified so that there are rules to follow and evidence to rely on. New products and technologies for SF6 power equipment are constantly emerging and developing rapidly. This equipment is characterized by miniaturization, modularity, and intelligence, and boasts high technological content. Maintenance and operation personnel must master the basic theoretical knowledge of SF6 power equipment and be proficient in relevant technical regulations, process standards, and operating procedures to ensure that SF6 power equipment performs its functions optimally.