Dielectric Properties and Synergistic Effect Evaluation Method of C4F7N Mixtures

In order to accelerate the screening and design of new eco-friendly insulating mixtures, ac breakdown tests were performed on nine binary
$\text{C}_{{4}}\text{F}_{{7}}\text{N}$
mixtures, specifically
$\text{C}_{{4}}\text{F}_{{7}}\text{N}$
mixed with rare gases (He, Ne, and Ar), conventional gases (CO2 and
$\text{N}_{{2}}$
), and fluorocarbon gases (CF4,
$\text{C}_{{2}}\text{F}_{{6}}$
,
$\text{C}_{{3}}\text{F}_{{6}}$
, and
$\text{C}_{{3}}\text{F}_{{8}}$
), under slightly nonuniform electric fields. The effects of pressure, buffer gas, and mixing ratio on the ac breakdown characteristics were analyzed. It is found that the ac breakdown voltages of the nine
$\text{C}_{{4}}\text{F}_{{7}}\text{N}$
mixtures increase linearly with increasing pressure. As the mixing ratio of
$\text{C}_{{4}}\text{F}_{{7}}\text{N}$
increases, the impact of the buffer gas on the ac breakdown voltages decreases. All
$\text{C}_{{4}}\text{F}_{{7}}\text{N}$
mixtures show the synergistic effects with segmented characteristics that transition from nonlinear to linear. And, the synergistic effect of
$\text{C}_{{4}}\text{F}_{{7}}\text{N}$
/CO2 mixture is the most significant. A new method for evaluating the degree of synergistic effects is proposed. Based on the synergistic effect evaluation coefficient
${N}$
and the dielectric strength of gas components, the dielectric strengths of binary mixtures can be calculated and predicted.