Study on the Dielectric Properties of C4F7N/N2 Mixture Under Highly Non-Uniform Electric Field

As an environment-friendly gas insulating medium, C4F7N has attracted great attention in recent years due to its excellent environmental protection and insulation performance. However, studies on the insulation performance of C4F7N/N-2 gas mixture are not comprehensive at present. In this paper, the breakdown and partial discharge characteristics of the C4F7N/N-2 gas mixture under highly non-uniform field were tested using the gas insulation performance test platform. The effects of gas pressure and mixing ratio on the negative partial discharge inception voltage (PDIV -), positive PDIV (PDIV+), and breakdown voltage of the gas mixture were analyzed. The engineering application potential of the C4F7N/N-2 gas mixture was also discussed considering the limitation of liquefaction temperature. It is found that an increasing gas pressure or a mixing ratio can effectively improve the insulation performance of the C4F7N/N-2 gas mixture. The breakdown properties of a gas mixture for a minimum operating temperature of -25 degrees C at 0.3, 0.4, 0.5, and 0.6MPa can reach 63.4%, 54.6%, 49%, and 56.4% of pure SF6, respectively, and the PDIV- can reach 80.4%, 66.9%, 62.8%, and 68.8% of pure SF6, respectively. Relevant results not only reveal the influence of the mixing ratio and pressure on insulation performance of the C4F7N/N-2 gas mixture, but also provide significant guidance for its engineering application.