Source: Power Window
In the power industry, SF6 is an important medium. It is used as arc extinguishing and insulating gas for closed medium and high-voltage switches . The excellent performance of SF6 gas enables economical and low-maintenance operation of the device. Save up to 90% space compared to regular units.
Sulfur hexafluoride (SF6) is a colorless, tasteless, odorless, non-toxic, non-combustible gas under normal conditions. Its molecular weight is 146.06, and its density is 6.139g/l, which is about twice that of air. It is one of the substances with the best chemical stability known, and its inertness is similar to nitrogen . It has excellent thermal stability and does not decompose in its pure state even at temperatures above 500℃.
Sulfur hexafluoride has excellent electrical insulation and arc extinguishing properties. Under the same conditions, its insulation capacity is more than twice that of air and nitrogen, and its arc extinguishing capacity is twice that of air.
The melting point of sulfur hexafluoride is -50.8℃. It can be used as a special refrigerant in the temperature range of -45 -0℃. Because of its good heat resistance, it is a stable high-temperature heat carrier.
Due to the above and other excellent properties, sulfur hexafluoride has been widely used in power, electronics, electrical industries and laser, medical, meteorological, refrigeration, fire protection, chemical industry, military, aerospace, non-ferrous metallurgy, physical research, etc. in recent years.
Bottled sulfur hexafluoride is a high-pressure liquefied gas and should be stored, transported and used in strict accordance with the "Gas Cylinder Safety Supervision Regulations" promulgated by the State Administration of Labor. When
is used, the cylinder valve should be fully opened. Use the pressure reducing valve to control the pressure and flow so that the gaseous state is filled into the equipment. After use, the valve should be closed tightly and a protective cap should be worn. The material in the cylinder cannot be exhausted, and the residual pressure in the cylinder should not be less than 0.2MPa at normal temperature.
Gas cylinders containing sulfur hexafluoride are not allowed to be used, stored and transported in environments above 45°C.
Liquid and gaseous SF6 can quickly cause suffocation, so the storage and use areas should be well ventilated and the cylinders must be prevented from leaking. Once inhaled, quickly move to fresh air.
Liquid sulfur hexafluoride has a sharp freezing effect. Do not let it come into contact with people's eyes, skin or clothes to avoid frostbite.
Sulfur hexafluoride product quality indicators
At present, there are no other technologies. From a technical, economic and ecological point of view, there is no better alternative than SF6 gas as an insulating and arc-extinguishing medium.
However, it is very important for users to understand the following processes: SF6 leaks should be avoided Gas situation inspection and regeneration methods Recycling , Purification and storage of used SF6 gas Purification to make SF6 reusable 1.1 Reuse of SF6 gas Nowadays, SF6 (sulfur hexafluoride) is mainly used in electrical equipment. It has been used as a gaseous insulating medium in switches for 25 years. If these equipment are to be overhauled, the SF6 gas should be re-entered into the economic cycle and should not be discharged into the atmosphere. If the quality indicator is met, the SF6 gas used in the equipment can be reused. From an ecological point of view, this method can minimize the leakage of SF6 into the atmosphere until it is only a trace leakage from the switch itself. The reuse of such a system as SF6 gas requires long-term quality control and strict compliance with quality standards in accordance with IEC376 (applicable to new gases) and IEC480 (applicable to used gases). DILO's equipment enables absolutely safe purification and regeneration of SF6 gas.1.2 Inspection of gas quality Long-term control of SF6 gas quality in switches is fundamentally beneficial. In this way, you receive information about the SF6 gas situation and the reliability of the switch operation. Therefore, the gas pollution situation can be judged in time and hidden dangers can be eliminated before it causes failure and serious damage to the switch. The following parameters should be measured before each gas recovery: Concentration of decomposition product
SF6 Dew point temperature
DILO's detection instrument can meet the following requirements: Short measurement time - portable and easy to operate The method of purification and regeneration can be determined based on the measurement results. 1.3 Recycling, purification and storage of used SF6 gas For the recovery and storage of SF6 gas, DILO offers various types of gas treatment units for the maintenance of medium voltage switchgears, outdoor circuit breakers and gas insulated switches . The appropriate recovery truck can be selected based on gas volume, cycle time and corresponding application. The DILO devices used - devices that can purify SF6 - have the following components: compressors :
All compressors used by DILO are absolutely oil-free. Some of them have a final pressure of 24bar (suitable for gaseous storage), and some can reach a final pressure of 50bar (suitable for liquid storage). vacuum compressor: recovery pump: The compressor and vacuum compressor work together to perform oil-free recovery of SF6 gas until the pressure in the air chamber reaches a minimum of 50mbar. However, an oil-free recovery pump can also be used to recover SF6 gas, which can reach a final pressure of 1mbar. vacuum pump: Before inflating, the air chamber must be evacuated to avoid mixing with air. For this purpose, we use oil-lubricated vacuum pumps, which only discharge to the atmosphere. They are used only to extract air. Before the gas chamber is refilled with SF6 gas, it can be evacuated to 1 mbar using a standard vacuum pump. We also offer the vacuum pump with higher final vacuum. filter unit - preset filter: When recovering SF6 gas from the circuit breaker , the gas will automatically flow through the dry filter and dust filter. Decomposition products, moisture and fixed dust are effectively trapped. For gases that are highly contaminated and of uncertain quality, it is absolutely necessary to install an additional pre-filter at the inlet front of the gas treatment device to protect it from decomposition products. The maintenance/inspection intervals for filter replacement depend on different factors and cannot be standardized. Therefore we recommend measuring the mass of the gas. 1.4 Purification of SF6 gas for reuse As we have already mentioned, each gas treatment unit is equipped with dry filters and dust filters. Dry filters safely adsorb gaseous decomposition products and moisture. The filter element is equipped with AL2O3 and a molecular sieve, which is easy to replace. No need to disassemble existing piping. The dust filter is used to filter solid dust and decomposition products in SF6 gas. The candle filter rod is wrapped in a cylinder and has a star-shaped cross-section. For dust with size ≥1.0um, the blocking rate is 100%. The purified SF6-gas is reused in the switch. SF6 gas can be purified on site in 95% of use cases. 4% of the gas is purified at the main station with corresponding equipment. Only about 1% of the gas cannot be purified. Manufacturers and operators of electrical switches can only use purified, qualified SF6 gas to recharge the switch. The purified SF6-gas can be charged back into the gas chamber using overpressure or a compressor. The required inflation pressure can be adjusted through the pressure reducing valve. Select the inflation pressure according to the adjustment range of the pressure reducing valve. The gas stored in liquid form flows through the evaporator. The evaporator comes with a thermostat . 1.5 Separation of SF6/N2 Air may be mixed into the SF6 gas if the gas is not handled properly or if pressure and vacuum sealing connections are not used. There are also some devices that are inherently filled with mixed gas.DILO standard gas treatment units cannot separate air and nitrogen from SF6 gas. However, the DILO-SF6/N2-separation device can purify the mixed gas with an SF6 content of 40-98% into an SF6-gas with an SF6 content of 99%. To purify this gas mixture, there are several methods: 1.6 Gas connections and their meaning in "The concept of SF6 reuse" In order to achieve the guaranteed minimum leakage rate of 1% p.a. (recently 0.5% p.a), a connection that meets these parameters is required. The DILO connection system for SF6-gas is the most widely used gas connection joint. When using this connection system, no leakage of SF6-gas can occur. Gas losses and mixing of gas with air are thus avoided. The advantages of this system are as follows: Pressure- and vacuum-tight Automatic connection when connected Automatic sealing when disconnected Metal-to-metal sealing principle, in the form of a tongue and groove; this way, it can be disconnected and reconnected as often as necessary, while the tightness of the SF6 remains unchanged.
SF6's high sealing performance. It has several types of DN6/DN8/DN20 and DN40. 1.7 Work protection device - indoor monitoring Work protection device: To handle the decomposed SF6 gas, the operator needs to take protective measures. Personnel working with SF6 gas must be aware of the possible hazards. Before opening the gas chamber, the gas quality and gas conditions in the switch must be known. Corresponding protective measures can be taken based on the measurement results. To give personnel the best protection, DILO provides work protection devices. The products in Work Protection Equipment comply with the information notes on accident prevention issued by the Employers' Liability Insurance Association. All products meet the required quality levels. Indoor monitoring: Since SF6-gas is five times heavier than air, lower rooms should be monitored to find out whether the concentration of SF6 exceeds the standard before people enter these rooms. For long-term monitoring of such rooms, DILO's SF6 alarm can be used. 1.8 Regulations for the storage and transportation of SF6 gas Regarding the storage and transportation regulations of new and used SF6 gas, please follow the regulations in force in your country. 1.9 SF6 gas contaminated by oil Using DILO's device will not cause oil pollution to SF6 gas. Once there is contamination caused by oil lubricated parts, the oil-contaminated SF6 gas must be recovered through a special separation filter. If the gas can no longer be regenerated, the gas must be returned to the manufacturer or supplier for processing. This gas should be filled into specially marked containers.
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