What is the temperature of high purity sulfur hexafluoride before it is liquefied?- SF6在线监测系统_SF6检漏仪_SF6传感器_SF6密度继电器

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What is the temperature of high purity sulfur hexafluoride before it is liquefied?

发布时间：2017-11-13 来源：ydlcb 浏览次数：41次

Sulfur hexafluoride molecular formula SF6, the relative molecular mass of 146.06, under normal temperature and pressure for colorless, tasteless, non-toxic, non-corrosive, non-flammable, non-explosive gas, density of about 5 times the air, the standard state density of 6.0886kg/ cubic meter. It is liquid at low temperature and under pressure and becomes a white solid when frozen. The sublimation temperature is -63.9℃, the melting point is -50.8℃, the critical temperature is 45.55℃, and the critical pressure is 3.759MPa.

Liquefied sulfur hexafluoride temperature: sulfur hexafluoride under one atmospheric pressure (i.e. 0.1MPa), the liquefaction temperature is -62℃; Under the pressure of 1.2MPa, the liquefaction temperature is 0℃. Generally, the pressure of sulfur hexafluoride gas charged into the circuit breaker is 0.35 ~ 0.65MPa (specifically determined by the ambient temperature at the time of inflation), and the liquefaction temperature is -40℃.

The electrical strength of sulfur hexafluoride is about 2.5 times that of air, and the arc extinguishing capacity is more than 100 times that of air, so it has completely replaced insulating oil and compressed air in the category of ultra-high pressure and ultra-high pressure, and has become the circuit breaker arc extinguishing medium. The critical temperature is the highest temperature at which the gas sulfur hexafluoride is converted into liquefied sulfur hexafluoride, and the critical pressure indicates the gas pressure required for liquefaction to occur at this temperature. Sulfur hexafluoride can only remain a gas at temperatures above 45 degrees, and it has the potential to become liquefied sulfur hexafluoride under normal conditions of use, so sulfur hexafluoride cannot be used at low temperatures and under too low pressure.

There was a problem with liquefied sulfur hexafluoride in the circuit breaker

The pressure of modern sulfur hexafluoride high-voltage circuit breaker is generally about 0.7Mpa, and the inflation pressure of the rest of the GIS in addition to the circuit breaker is generally not more than 0.45MPa. If the inflation pressure at 20 ° C is 0.75MPa (equivalent to the working pressure commonly used in circuit breakers), the corresponding liquefaction temperature is about -25 ° C, if the inflation pressure at 20 ° C is 0.45MPa, the corresponding liquefaction temperature is 40 ° C, it can be seen that there is generally no liquefaction problem. Only in high cold areas need to use heating measures on the circuit breaker, or use sF6-N2 gas mixture to reduce the liquefaction temperature.

New measures to prevent the liquefaction of sulfur hexafluoride gas

A heating device is installed outside the breaker sulfur hexafluoride gas storage tank, which is composed of temperature controller, AC contactor and electric heater, and is comprehensively monitored by the anti-liquefied sulfur hexafluoride management system. Use 220V AC power supply, each phase heating power is 200W, when the internal temperature of the heating device is lower than -10℃, the device automatically input, start heating, heat through the insulated electric heating belt, in the form of insulation and heat conduction to the sulfur hexafluoride gas storage tank metal shell, and then transferred to the sulfur hexafluoride gas inside the circuit breaker. The outside of the heating device is sealed with rubber and plastic insulation material, which can prevent heat loss. When the internal temperature of the heating device reaches 50 ° C, the temperature control device automatically stops and starts heat preservation.

Because high-purity sulfur hexafluoride is an inert gas and is insoluble with oil, the mixed oil can be separated relatively easily. With the use of advanced technology, the oil filtration level has reached the same level as the oil-free system, which can remove the oil content fairly thoroughly.

At present, there are two main recovery and storage principles of high-purity sulfur hexafluoride recovery inflatable device, one of which uses the principle of freezing liquefaction method: That is, in the process of SF6 gas recovery, under a certain SF6 gas pressure, the refrigeration unit is used to reduce the temperature of SF6 gas to the saturated steam temperature under the pressure, SF6 gas begins to liquefy into a liquid, and is stored in a liquid form, and the advantage is that the recovery speed is fast and the liquefaction speed is fast.

The other is the principle of high-pressure liquefaction method, that is, in the process of high-purity sulfur hexafluoride recovery, at the ambient temperature at that time, the compressor is used to increase the pressure of SF6 gas to the saturated steam pressure at that temperature, and SF6 gas begins to be transformed into a liquid and stored in liquid form.

The advantage of sulfur hexafluoride recovery and purification device is that the system is simple, the disadvantage is that the system working pressure is high, the recovery rate is low, when the SF6 gas temperature (SF6 gas compressed by the compressor temperature can reach 80℃ or more) exceeds the critical temperature of 45.5℃, it can not be liquefied. At this time, the high-temperature and high-pressure SF6 gas can only be converted into a liquid after a period of time when its temperature drops below the critical temperature.