Action mechanism of insulating gas

Isolation is actually achieved by insulating the gas molecules and the free electron interaction between the poles to suppress the electron avalanche and thus increase the breakdown voltage. Electron avalanche refers to the phenomenon that when the electric field intensity is large enough, the free electrons generated between the poles are accelerated and continuously ionized by collisions with gas molecules, resulting in an avalanche increase in the number of free electrons. A voltage break occurs when the number of free electrons between the poles reaches a certain level.

Thus, the insulating strength of a substance can be measured by its breakdown voltage in an electric field. According to the insulating strength data of many substances measured, it can be concluded that the insulating properties of substances are closely related to molecular weight, molecular structure and electronic affinity. Strong electron affinity is beneficial to trapping free electrons and hinders the development of collision ionization. High molecular weight significantly reduces the mean free path of charged particles formed by trapping free electrons, thus improving the insulation strength of the molecule. F is the most electronegative element in the entire periodic table and has the strongest electron affinity. From the point of view of insulation, as many F atoms as possible should be introduced into the insulating gas molecule to improve its insulation strength. In addition, studies have shown that the existence of multiple bonds such as carbon-carbon double bonds, triple bonds and cyanogroup in the molecule can further improve its insulation strength.

Reasons for the poor environmental benefit of insulating gas SF6

SF6 is the most widely used insulating gas due to its excellent insulation and arc extinguishing properties. SF6 is also the most potent greenhouse gas known. According to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), SF6 has a greenhouse capacity of about 23,500 times that of carbon dioxide. The main reasons for this are as follows: First, SF6 is very stable in the atmosphere. According to current studies, the degradation pathways of SF6 in the atmosphere mainly include photodegradation and electron adsorption, but the reaction rate is very slow and the residence time in the atmosphere can reach 3200 years. Second, SF6 has an extremely strong infrared absorption near 948 cm-1, which is located in the "atmospheric window region" in the range 800-1200 cm-1. Its capacity to absorb long-wave radiation from the Earth's surface can be more than 42,000 times that of carbon dioxide.