Research on Arc Extinguishing Performance of C4F7N/CO2 Gases With Slight Positive Pressure

C₄F₇N is a new environmentally friendly gas that can replace SF₆. Its insulation ability and interruption performance at high pressure have been proved. But the arc extinguishing performance at slight positive pressure has not been studied yet. In this article, the arc extinguishing performance of the C₄F₇N/CO₂ gases with slight positive pressure in a 12-kV ring-main unit (RMU) is tested in the synthetic test circuit. The voltage characteristic and the dielectric recovery strength of the mixture are measured, and compared with those of SF₆. A high-speed camera is used to observe the arc shapes and arc movement of the two gases. The experimental results show that at the slight positive pressure (0.14 MPa, absolute atmosphere), the arc voltage of the C4 mixture is similar to that of SF₆, but the peak voltage of the C4 mixture is lower and the arc column is wider than that of SF₆. And the arc of the C4 mixture is more prone to back commutation. At the same breaking current, the dielectric recovery strength of the C4 mixture is about 34% of SF₆. For 12-kV RMU, the interruption capability of the C4 mixture can meet the requirements of the IEC standard for load switch. According to experiments, the interruption capability of the C4 mixture can be further improved by optimizing the arc extinguishing structure.