Abstract
As an environmentally friendly gas with good insulation and stable chemical properties, CF3I gas mixture is considered as a potential alternative to SF6 gas to compensate for the shortcomings of SF6 gas as a greenhouse gas. This article attempts to study the CF3I ternary gas mixtures with c-C4F8 and N2 by considering the process of streamer development in surface discharge. The model of surface discharge in CF3I gas mixture under DC voltage was established by COMSOL, and the drift-diffusion equations of particles was solved to show the discharge process, and the changes of electric field and particle concentration, etc. during the development of streamer were obtained, which provides the theoretical basis for the reliable diagnosis of partial discharge. On this basis, the model is compared with models for two other different gases (SF6/N2, artificial air) in terms of particle characteristics, streamer characteristics and streamer branches characteristics. Finally, it is concluded that under this model, although the insulation characteristics in CF3I gas mixture are weaker than those in SF6, the difference is not large and both are much better than those in artificial air, so c-C4F8/CF3I can be considered as a potential substitute for SF6.
Highlights
SF6 is a colorless, odorless, non-toxic and non-flammable gas with stable chemical properties and good insulating properties, so it is widely used in electrical equipment [1]
The attachment cross section of c-C4F8 is from Ref. [28], the ionization cross section of c-C4F8 is from Ref. [29], and the elastic cross section and excitation cross-section are from Ref. [8]
There is a voltage on the needle electrode, and the initial electrons will move away from the needle electrode, i.e., toward the high potential, and during the movement they will collide and react with the neutral molecules N2, CF3I and c-C4F8 in the environment, producing new electrons, positive and negative ions
Summary
SF6 is a colorless, odorless, non-toxic and non-flammable gas with stable chemical properties and good insulating properties, so it is widely used in electrical equipment [1]. After that, based on Boltzmann simulation method, they studied and analyzed c-C4F8/CF3I gas mixture in terms of electron energy distribution function (EEDF), reduced effective ionization coefficient, critical reduced electrical field strength, electric field sensitivity coefficient, and so on [6]. Li et al, studied the properties of negative surface discharge in artificial air and discussed the effect on the streamer characteristics under different applied voltages and different relative dielectric constants of the insulator [18]. The gases they chose were generally air or SF6 and its mixtures, and little research has been done to discuss some of the phenomenon that occur when the streamer conducts the electrode. Where ε0 is the vacuum dielectric constant, V is the space electric potential, and e is the elementary charge
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