SF6 is a colorless, odorless, non-toxic and non-flammable gas with extremely stable chemical properties. It has excellent arc extinguishing and insulation properties and is widely used as insulation or arc extinguishing medium in power equipment. Taking gas-insulated metal-enclosed switchgear as an example, it mainly consists of circuit breakers, isolation switches, ground switches, fast grounding switches, voltage transformers, busbars and bushings, etc. Each component is filled with SF6 gas at a certain pressure. If the micro water (trace water) in SF6 gas exceeds the standard or the density abnormally decreases (due to leakage, etc.), it will seriously affect the electrical performance of the equipment, resulting in equipment tripping or insulation breakdown. Therefore, monitoring the density and micro water of SF6 gas in operating power equipment is very important.
Take GIS equipment as an example. At the time of factory delivery, each SF6 gas chamber is equipped with a mechanical SF6 relay (density gauge) to monitor the density of SF6 gas (P20 pressure). When the SF6 gas leaks to a certain pressure, the relay will trigger an alarm contact or locking contact, and show the current gas pressure through the local display pointer. GIS equipment is not equipped with an SF6 gas micro water monitoring device at the time of factory delivery, and users need to use a portable dew point meter to carry out off-line micro water detection of each gas chamber regularly (generally once every six months). Compared with the above-mentioned traditional SF6 gas density micro water detection method, the SF6 gas density micro water online monitoring system has the following advantages.
Although the sf6 gas density relay can display sf6 density in real-time through the local display pointer, it relies on on-site inspection by operators, which is unable to meet the needs of more and more unmanned substations today. The interval cycle of using a portable dew point meter to detect micro water in the SF6 gas chamber can be several months, and the real-time performance is poor, unable to determine when the micro water started to exceed the standard. The SF6 gas density micro water online monitoring system can achieve 24-hour uninterrupted SF6 gas density micro water monitoring, which is conducive to the timely discovery of SF6 gas leakage and micro water over-standard, and determining the severity of the problem, so as to arrange equipment maintenance work more scientifically and reasonably.
In medium and large-sized substations, the number of SF6 gas chambers in GIS equipment alone can reach hundreds or even more. A portable dew point meter can only accurately monitor micro water in 4-5 gas chambers per hour (calculated based on a single dew point meter), so it requires a large amount of manpower and material resources to complete the micro water monitoring of all SF6 gas chambers. After using SF6 gas density micro water online monitoring system, there is no need for manual monitoring anymore.
Although SF6 gas itself is non-toxic and harmless to human beings, it is a kind of greenhouse gas. Its single-molecule greenhouse effect is 22,000 times that of carbon dioxide, and it is one of the six greenhouse gases prohibited from emissions in the Kyoto Protocol. When using a portable dew point meter to monitor micro water in SF6 gas chamber, it is necessary to continuously discharge a part of SF6 gas to ensure accurate monitoring results. Monitoring one SF6 gas chamber requires discharging about 8 L of SF6 gas, which is difficult to recover. After using SF6 gas density micro water online monitoring system, the monitoring process can achieve zero emission of SF6 gas.
Based on the above technical advantages of SF6 gas density micro water online monitoring system, online monitoring of the density and micro water of SF6 gas in power equipment is the future development direction.