What are the two main factors affecting the gas insulation performance of sulfur hexafluoride (SF6)?- 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 are the two main factors affecting the gas insulation performance of sulfur hexafluoride (SF6)?

发布时间：2019-07-13 来源：ydlcb 浏览次数：33次

Sulfur hexafluoride (SF6) gas is a non-toxic, colorless, tasteless, chemically stable substance with excellent arc extinguishing and insulation properties. Electrical equipment that replaces insulating oil with SF6 gas as an arc extinguishing and insulating medium is called SF6 electrical equipment. At present, SF6 electrical equipment has been used in the power grid on a large scale, and the types have been extended to current transformer (CT), voltage transformer (PT), capacitors, SF6 combined electrical equipment (GIS).

The factors that affect SF6 gas breakdown voltage are as follows:

(1) Uniformity of electric field. The breakdown voltage of SF6 varies greatly in different uniform electric fields. In a uniform electric field, the breakdown voltage of SF6 is larger than that in a highly non-uniform electric field, and this effect is much greater than that of air.

(2) SF6 working pressure. Increasing the working pressure of SF6 is one of the ways to increase the breakdown voltage of SF6, but the working pressure should not be too high, otherwise SF6 will liquefy. At the same time, it should be noted that the breakdown voltage of SF6 tends to be saturated with the increase of air pressure, and the more uneven the electric field, the easier it is to saturate. Therefore, it is only effective to increase SF6 working pressure under the condition that SF6 is liquefied and the electric field is fairly uniform.

(3) SF6 gas is an impurity. When the SF6 is mixed with air, nitrogen and other impure gases or conductive particles, its insulation capacity can be significantly reduced. The conductive particles of SF6 gas move under the action of electric field, and gradually form a "conductive bridge", resulting in a decrease in breakdown voltage.

(4) Electrode surface. The breakdown voltage of SF6 decreases with the increase of electrode surface area. The rougher the electrode surface, the lower the breakdown voltage. After multiple discharge treatment, the electrode surface is smooth, and the breakdown voltage has a tendency to increase.

SF6 gas insulation strength is affected by the following factors:

(1) Influence of electric field uniformity. Under a uniform electric field, the insulation strength increases linearly with the increase of the distance between contacts. When the distance is too large, the insulation strength increases and saturation occurs due to the uneven electric field. Under uneven electric field, its insulation strength will even approach the level of air.

(2) The relationship with pressure, under a more uniform electric field, the insulation strength increases with the increase of gas pressure, but it is affected by the thickness of the container wall and the volume of the internal components of the equipment. You can't raise the gas pressure too high. Generally, at 20℃, the pressure of SF6 gas chamber is 0.3-0.6mpa, and the pressure of SF6 arc extinguishing chamber is 0.5-0.7mpa.

(3) The influence of electrode surface state. Generally, the rougher the electrode surface, the lower the breakdown voltage. The larger the electrode area, the greater the probability of accidental factors, thus reducing the breakdown voltage.

(4) The influence of voltage polarity, because the insulation structure of the SF6 circuit breaker is a slightly uneven electric field form, its insulation level is often determined by the complex polarity voltage.

The content of water vapor in SF6 gas, which is commonly referred to as humidity or trace moisture. When the trace moisture increases or seriously exceeds the standard, it may cause flashover along the internal surface of the insulation and cause accidents, and may also cause the switch insulation parts to be damp or produce condensation, thus greatly reducing its insulation performance. At the same time, the water will react with the sulfur hexafluoride decomposition by the arc to produce highly corrosive HF (hydrofluoric acid), thionyl fluoride (SOF2), sulfuryl difluoride (SO2F2) and other acidic substances, which will corrode the metal components in the arc extinguishing room of the equipment and the sealing insulation materials of the equipment, affecting the mechanical properties of the equipment and shortening the service life of the equipment. Reducing the insulation capacity of the equipment is also toxic to the human body and will cause pollution to the environment. The standard of trace moisture in the gas of sulfur hexafluoride electrical equipment in operation is as follows: equipment containing arc extinguishing chamber: 300μι/ ι; Equipment without arc extinguishing chamber: 500μι/ ι(20 ° C).

The second is the density of sulfur hexafluoride gas, the density of sulfur hexafluoride gas at 101325Pa, 20℃ is 6.16g/L, with excellent insulation and arc extinguishing electrical performance to ensure a certain density of SF6 gas, in order to maintain good arc extinguishing and insulation performance, and the density of SF6 gas and pressure curve is a proportional function, that is, Ensure a certain pressure, in order to ensure a certain density value. These two factors are directly related to the sealing performance of SF6 electrical equipment, and the sealing performance of SF6 electrical equipment refers to the ability and condition of each sealing link of the electrical equipment to seal the gas.