专注于SF6气体检测的专业化
Why does SF6 sulfur hexafluoride not burn?
SF6 molecules are easy to adsorb free electrons and form negative ions, which have strong electronegativity. However, under a certain electric field, it is difficult for these ions to accumulate enough energy to ionize the gas. At the same time, because the free electrons in the gas are reduced, the harm of these electrons easily causing the gas to be broken down is also reduced. Therefore, SF6 gas has good insulation performance, and the insulation strength of SF6 is 2-3 times greater than that of air in a uniform electric field, and under 0.3Mpa pressure, the insulation strength exceeds that of transformer oil. However, in an uneven electric field, its insulation strength will decrease, so the components of the sulfur hexafluoride circuit breaker are mostly concentric circles to make the electric field uniform.
SF6 molecule has strong electronegativity, which makes SF6 have strong arc extinguishing ability. Because SF6 molecules become negative ions after adsorption of free electrons, negative ions are easy to combine with positive ions to form neutral molecules, so that the electrical conductivity of the arc space quickly disappears. Especially when the arc current is close to zero, this effect is more significant. If SF6 gas is used to blow the arc, a large number of fresh SF6 molecules are constantly in contact with the arc, and the arc is extinguished more rapidly. Due to the strong arc extinguishing ability of SF6 gas, the change rate from conductive arc to insulator is particularly fast, so the breaking current of SF6 circuit breaker is large, and the breaking time is short. Under the same voltage level, the same breaking current and other conditions are the same, SF6 circuit breakers have fewer series breaks.
SF6 gas is a molecular gas with many atoms. The decomposition and ionization of SF6 gas under high arc temperature is very complicated. The arc center part of SF6 gas has low thermal conductivity, high temperature and large conductivity, and the outer flame part has high thermal conductivity, low temperature and small conductivity, so the arc current is almost concentrated in the arc center part. Therefore, in SF6 gas, you can see a very thin, very bright arc, and you can hardly see the external flame site. This is also one of the reasons for the short arc extinguishing time of SF6 gas. When the arc current is reduced to zero, SF6 molecules are significantly electronegative at this time, so that the current is continuous, and the small arc center can exist to a very small current range. This feature of SF6 arc makes the circuit breaker break a small current, and will not produce an operating overvoltage due to the intercepting effect.
SF6 gas has a high insulation strength for the following reasons:
(1)SF6 gas has a strong electronegativity. The F atom in its outer layer is one of the elements with strong negative electric characteristics in the halide element, has a strong ability to attract electrons, and is easy to combine with free electrons to form negative ions, SF6 +e-*SF6 hinders the formation and occurrence of discharge.
(2) SF6 molecule diameter is large o SF6 molecule is easy to obtain free electrons, so that its molecular volume increases, the free stroke becomes shorter, and it is not easy to accumulate energy in the electric field, thus reducing its ability to collision ionization.
(3) The molecular weight of SF6 is more than five times that of air. The mobility of ions is smaller, making it easier for positive and negative ions to compound, and the charged protons are reduced, thus greatly enhancing the SF6 insulation strength.