Abstract
Sulfur hexafluoride, SF6, is a common dielectric medium for high-voltage electrical equipment, but because it is a potent greenhouse gas, it is important to find less environmentally harmful alternatives. In this paper we explore the use of CO2 and O2 as one alternative. We studied the synergistic effect in a mixture of CO2 and O2 from both macroscopic and microscopic perspectives. The effect leads to a dielectric strength of the mixture being greater than the linear interpolation of the dielectric strengths of the two isolated gases. We analyzed the critical reduced electric field strength, (E/N)cr, the breakdown gas pressure reduced electric field, E/p, and the breakdown electron temperature, Tb, and their synergistic effect coefficients for various CO2 concentrations and various products of the gas pressure times the gap distance (pd). A gas discharge and breakdown mechanism in a homogenous electric field is known to be controlled by the generation and disappearance of free electrons, which strongly depend on the electron temperature. The results indicate that adding a small amount of O2 to CO2 can effectively improve the value of (E/N)cr and bring a clear synergistic effect. In addition, significantly different variation trends of the synergistic effect in the E/p and Tb of CO2-O2 mixtures at various CO2 concentrations and pd values were also observed.
Highlights
Stable gases with good electrical properties are commonly used as insulating and arc-quenching mediums for electrical equipment.[1,2] SF6 is considered to be the most excellent insulating and arcquenching medium for electrical equipment.[3]
This gas is a strong greenhouse gas gas—its global warming potential (GWP) is 23 900 times greater than CO2—and has been designated a regulated gas at COP3 (3rd session of the Conference of the Parties in the United Nations Framework Convention on Climate Change) in 1997.4 In order to deal with this issue, lots of efforts have been performed on the exploration of the substitute for SF6.5–10
The energy distribution function (EEDF) values for relatively low electron energies increase with increasing CO2 concentrations
Summary
Stable gases with good electrical properties are commonly used as insulating and arc-quenching mediums for electrical equipment.[1,2] SF6 is considered to be the most excellent insulating and arcquenching medium for electrical equipment.[3]. Finding the best mixture for buffering gases and the optimal ratio of them is very important. For dielectric strength of a gas mixture, the synergistic effect is usually used to evaluate and optimize the choice of gases in the mixture, the mixed ratio, and the gas pressure.[1,2] In this context, the synergistic effect leads to a dielectric strength of a mixture of two gases being greater than the linear interpolation of the dielectric strengths of the two isolated gases. It is important to differentiate the term synergism in the present study from the term positive synergism, which indicates that the dielectric strength of the gas mixture exceeds that of the pure gas components. This investigation is limited to a consideration of synergism, not positive synergism
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