SF6 appeared in the early twentieth century, it is a gas formed when sulfur is burned in fluorine gas. SF6 gas in its normal state is a colorless, odorless, non-toxic, non-combustible chemically stable gaseous material, its density is about five times that of air. Due to its molecular negativity, it has a strong ability to form negative ions by adsorbing free electrons, thus its high electrical strength and excellent insulation properties. With its low dissociation temperature and large dissociation energy, it is also a gas with excellent interrupting performance. sf6 gas is gradually used as a new insulating medium for electrical equipment because of its excellent insulating performance and interrupting performance as well as the property that its gas cannot be burned.
SF6 load switch is a kind of switchgear that integrates load switch, isolation switch and grounding switch, sealed in a box full of SF6 gas, and uses the excellent insulation and arc extinguishing properties of SF6 to meet the functions of closing, isolating and grounding. It has the advantages of simple structure, reliable interlocking, small size, less maintenance, safe and easy installation, etc. It is suitable for different applications.
Since SF6 load switch and current-limiting fuse can better protect transformers, they are commonly used abroad. In industrially developed countries (such as Europe and Japan), the ratio of circuit breaker to load switch is 1:5~6. In China, with the continuous development of urban network construction and transformation, the application of load switch equipment in 12kV distribution system for ring network power supply and terminal power supply is also increasing. At present, most of the domestic SF6 load switch market is still mainly occupied by foreign companies (such as ABB, Schneider, etc.), and dozens of domestic manufacturers have developed and produced various different models of SF6 load switches (such as Wenzhou Kaiyuan, Ningbo Tianan, Zhenjiang Longyuan, etc.). Domestic manufacturers have a more comprehensive and profound understanding of SF6 load switch by digesting and absorbing rich design, manufacturing and operation experience from abroad, and the quantity and quality of domestic SF6 load switch has been steadily improved.
Cabinet SF6 gas insulated switchgear (referred to as C-GIS inflatable cabinet), is a new high-tech series of products developed abroad in the last decade or so, gradually becoming an important variety of metal-enclosed switchgear. China has only started in recent years.
C-GIS inflatable cabinet is all high-voltage components such as busbars, circuit breakers (or load switches), disconnecting switches, transformers, etc. enclosed in a stainless steel shell filled with low pressure SF6 gas medium-voltage complete equipment. Its outstanding features are safety, high reliability, simple operation, maintenance-free, easy installation, etc.. The most important feature is that it is not affected by external environmental conditions, such as condensation, dirt, small animals and chemical substances, etc., and can be used in places with harsh environments. Another important feature is that, due to the use of excellent performance of SF6 insulation greatly reduces the size of the cabinet, which is conducive to the development of miniaturization direction. Compared with the air insulation, the installation area of SF6 inflatable cabinet is 26% and the volume is 27%, meanwhile, because the inflatable cabinet is equipped with good performance of oil-free switch, it greatly reduces the maintenance and overhaul workload. It is suitable for the requirements of network nodes or user terminals, and also meets the requirements of various secondary SF6 load switches, inflatable cabinets, domestic and foreign product composition and their development forms, as well as the conditions and technical problems that must be available for the production of such products. SF6 appeared in the early twentieth century, it is a gas formed when sulfur is burned in fluorine gas. SF6 gas in its usual state is a colorless... The need for flexible use of compact switchgear in substations. Especially suitable for airports, subways, railroads and other occasions with high power requirements, C-GIS adapts to the requirements of miniaturization and intelligence.
The massive use of SF6 gas in switchgear has promoted the rapid development of switchgear manufacturing. However, SF6 gas decomposes to form low fluoride of sulfur during arc discharge, and these decomposition products are both toxic and corrosive to many insulation materials and metal materials. In addition, SF6 gas has a certain influence on the ambient temperature (greenhouse effect). In 1991, the former Ministry of Electrical and Mechanical Services issued the notice "SF6 High Voltage Switchgear Production Plant Requirements" to ensure the quality of SF6 switchgear production. The requirements for SF6 high-voltage switchgear production plants of 35kV and below are set out. In brief.
High-voltage switchgear production plant to produce SF6 load switch and inflatable cabinet switchgear, mainly to solve technical problems in the following areas.
Leakage rate has been the focus of attention of the manufacturers and users. SF6 load switches and inflatable cabinets have an annual leakage rate of less than 1% / year. The service life of the switch is generally around 30 years. Sealing should take into account the compression of sealing components, life, aging, and reliability aspects.
SF6 load switches generally use sealing rings to achieve static and dynamic sealing of the gas (such as ABB's SFG, Schneider's SM6 switch); there are also very few stainless steel welding and sealing ring combination of sealing forms (VEI's SF6 switch); C-GIS inflatable cabinets are sealed by welding sealing, sealing ring sealing and metal bellows sealing. Adopted welding seal, to ensure the gas tightness of the weld, the general welding equipment and welding technology can not meet the requirements, at least with argon arc welding or laser welding equipment for welding (at present, there are also several domestic production equipment from foreign imports of welding robots), to ensure the quality of welding.
Also consider the impact of environmental factors on the sealing performance, such as high or low temperature conditions to meet the requirements of sealing performance.
SF6 gas moisture content is one of the main testing indicators of SF6 switch quality, and its size directly affects the insulation level of the switch.
For new SF6 gas, the first thing to check is the moisture content of the gas itself, which does not exceed the specified value (the general moisture content is 15 ppm).
When evacuating and inflating SF6 switchgear, use high purity nitrogen or sulfur hexafluoride gas to clean the inflatable pipeline, control the moisture content in the pipeline, and develop a standardized SF6 switchgear production process.
The quality of parts is directly related to the quality of the product, SF6 load switch and inflatable cabinet are maintenance-free or less maintenance switchgear, once the quality of the parts inside the sealed box, it will most likely be scrapped into the whole switchgear.
To ensure the quality of components, we must strictly control the materials, processing technology and inspection methods of the components, their mechanical strength, electrical performance and other parameters to meet the requirements of the product. More stringent inspection of the parts required to be installed, the entire assembly process requires a more rigorous process control and process inspection control, to ensure the correctness and consistency of the assembly. In particular, the lubrication of the transmission links and contact surfaces within the sealed case should be permanently effective throughout the product life cycle, the contact pressure of the contacts should be strictly controlled, and the resistance value of the main circuit of the switch should meet the product technical requirements during the life cycle.
With the rapid development of social economy, the growing urban electricity load and the increasing demand for power supply reliability, the high-performance ring network distribution, multi-loop distribution and switchgear have become one of the irreplaceable and important equipment in the secondary distribution system, especially the compact and scalable SF6 switchgear has become the leading equipment in the secondary distribution system. With the wide application of digital technology, integrated technology and mechatronics technology, SF6 switchgear will be more developed.
