Safety management measures for SF6 gas- 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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Safety management measures for SF6 gas

发布时间：2018-10-25 来源：ydlcb 浏览次数：33次

Safety management measures for SF6 gas

SF6 gas at room temperature, atmospheric pressure is a colorless, odorless, non-toxic and non-combustible gas, its chemical properties are very stable, at 20 ° C and 101325Pa density of 6.08 g/L, about 5 times the density of air, SF6 gas critical temperature of 45.6 ° C, compressed and liquefied, usually liquid into the cylinder transport.

The electrical insulation and arc extinguishing properties of SF6 gas are very strong. The molecular weight of SF6 is 5 times that of air, so SF6 ions in the electric field running speed than nitrogen, oxygen plasma in the air is much smaller, more prone to compound, fluorine ions reduce the gas charged particles, greatly improve the insulation level of the gas, about 3 times that of air. Fluorine is the most electron affinity of all elements, so SF6 has a strong electronegativity, a great ability to attract electrons, and it is easy to form negative ions, so the arc extinguishing performance of SF6 gas is 100 times that of air. Therefore, SF6 gas is widely used in electrical equipment, and is the substance with the insulation and arc extinguishing performance found at present.

Pure SF6 is an inert gas, and the discharge in the equipment will cause the decomposition of SF6 gas, and its decomposition products are incompatible with the structural material. SF6 gas produces gas decomposition under the action of arc, most of the decomposition is sulfur and fluorine single atoms, after the arc is extinguished, most of it can be reduced, only a few parts in the process of recombination with free metal atoms and water chemical reaction, resulting in metal fluoride and HF toxic and corrosive substances.

By SF6 (http://www.kdgc.cn/GetKnowledge/zh-cn/High_purity_gas/SF6.aspx), pressure and temperature curve analysis shows that the liquefaction curve on the right side, when the temperature change of gas density remains the same, only the change of the present pressure, That is, the insulation strength and arc extinguishing performance are unchanged, but when the temperature of the gas drops to the liquefaction temperature and continues to decline, the gas will liquefy, and its pressure and density will decline quickly. At this time, the arc extinguishing insulation performance of the gas should be rapidly reduced, so the SF6 equipment is not allowed to operate at a temperature lower than the liquefaction temperature.

SF6 is also a chemically extremely stable gas, with an atmospheric lifetime of about 3,200 years. In particular, SF6 has a strong ability to absorb infrared radiation, that is to say, SF6 is a gas with a strong greenhouse effect, such as taking 100 years as the baseline, its potential greenhouse effect is 23,900 times that of CO2. In addition, the SF6 gas currently emitted into the atmosphere is increasing at a rate of 8.7%. It should be noted that the greenhouse effect of SF6 has not been discovered in the past, but because the concentration of SF6 gas in the Earth's atmosphere is very low, it is considered to have a small impact and has not been seriously considered. The emissions to the atmosphere mentioned here do not refer to the natural leakage of GIS and GIT devices, which is less than 1/1000 per year, which is completely negligible. The leakage referred to here mainly refers to the emissions of the product during manufacturing, installation, field commissioning and maintenance.

1. Check the moisture content of SF6 gas regularly

If it is found that its content exceeds the allowable value, effective measures should be taken, including gas purification treatment, replacement of adsorbent and SF6 gas, equipment disintegration and maintenance countermeasures. The main sources of water inside SF6 equipment are: ① water contained in SF6 new gas; ② Moisture entering the equipment during assembly; (3) Water released from solid insulating objects; ④ Water infiltrated through the seal during operation; (5) Water entered during multiple air replenishment and testing during operation; ⑥ air chamber adsorbent failure.

There are many methods for measuring the moisture content in SF6 gas. At present, there are three kinds of instruments: electrolytic moisture meter, resistance-capacitance dew point meter and mirror dew point meter. Among them, the mirror dew point instrument has high accuracy, the resistance and capacitance dew point instrument has a wide measuring range, and the field operation is convenient to use the resistance and capacitance dew point instrument. At present, domestic only electrolytic moisture meter, cheap; Mirror dew point meter and resistance dew point meter rely on imports, the price is expensive, about 30 times that of domestic, but easy to use and accurate.

2. Regular leak detection of SF6 gas

SF6 gas leak inspection is divided into qualitative and quantitative inspection, qualitative inspection is directly on the equipment of the joint sealing point aluminum castings to detect the location of the equipment leakage points. Quantitative inspection is to find out the leakage amount by bandaging detection, bottle hanging method or pressure conversion, so as to obtain the annual leakage rate.

Qualitative leak detection has two methods: vacuum leak detection and leak detector detection:

① Vacuum leak detection method is to vacuum the equipment to 40Pa, stop the pump 0.5h, read A number on the vacuum meter, then stop 5h, read B number, if B-A ≤133Pa, it is considered that the seal is good;

② Leak detector Leak detector is to move the leak detector probe along the surface of the equipment and the surface of the aluminum casting, and judge the gas leak according to the reading of the leak detector.

When detecting leaks, the detector should pay attention to: the moving speed of the probe should be slow to prevent the probe from moving too fast and missing the leak point; Leak detection should not be in the case of high wind speed, to avoid leakage gas blown away by the wind and affect the leak detection; The leak detector chooses a leak detector with high sensitivity and small response speed. Generally, the minimum detection amount of the leak detector is < lppm, and the response speed is < 5s.

Quantitative leak detection usually adopts buckle method, bottle hanging method, local dressing method, pressure drop method and other methods. The buckle cover method is suitable for high-voltage circuit breakers and small equipment suitable for making covers, the hanging bottle method is suitable for flanges with double channel sealing slots, the local dressing method is generally used for assembling units and large products, and the pressure drop method is suitable for measuring the leakage rate of the equipment compartment when the leakage is large or during operation. In general, in the acceptance test of SF6 equipment, the leak detection work uses the local dressing method and the buckle method.

3 Pay attention to ventilation

Qualified SF6 gas is non-toxic, but there is a risk of suffocation, SF6 gas should be stored in a well-ventilated place, and to sunscreen, moisture-proof. Before entering the low area, the staff should test the oxygen content in the area, if the oxygen content is found to be lower than 18%, they can not enter the area.

4 Wear protective gear

When gas sampling operations and handling general leakage, wear a gas mask under ventilation conditions.

In short, safety is the basis of power production, prevention is the key to ensure safe production, should constantly improve and improve the power equipment operation of organizational measures and technical measures.