Partial Discharge and Decomposition Characteristics of C4F7N/CO2/O2 Under Metallic Protrusion Defects

C4F7N/CO2/O2 gas mixtures have become the most promising gaseous insulating medium to replace SF6in the electric power industry due to their excellent environmental and insulating properties. Although the addition of O2 can enhance the insulating performance and chemical stability of C4F7N/CO2 gas mixture to a certain extent, the influence of O2 addition and its content change on the gas by-product generation characteristics of the gas mixture under the action of PD is not clear. In this paper, experiments on C4F7N/CO2/O296h PD and its decomposition characteristics were carried out through needle-plate electrodes simulating metal protrusion defects in the device, and it was found that the addition of 2-4% O2 to the C4F7N/CO2 mixture could significantly inhibit the generation of most of the by-products, and that the cumulative discharge per second and average discharge per second increased dramatically when the O2 content was greater than 6%, resulting in the aggravation of the decomposition of the gas mixture.

I. Introduction

In recent years, SF6 has been widely used in various types of gas-insulated electrical equipment due to its excellent performance ^[1]–[3]. However, SF6 has a Global Warming Potential (GWP) of 23,500 times that of CO₂ and an atmospheric lifetime of 3,200 years, which makes it an extremely greenhouse gas insulating medium, and the Kyoto Protocol lists SF6 as one of the six greenhouse gases whose use is restricted globally^{[4], [5]}. Therefore, there is an urgent need to find an environmentally friendly gas insulation medium to replace SF_6.C₄F₇N insulation strength is two times that of SF_6, its GWP value is 2090, and its ozone depletion potential (ODP) is zero, the ternary gas mixture composed of C₄F₇N,CO₂ and O₂ is considered to be one of the most promising environmentally friendly insulating gases because of its excellent performance ^[6]–[9].