Partial Discharge Characteristics of Fluoronitriles/CO2 and Trifluoroiodomethane/CO2 Gas Mixtures under DC Voltage

Due to the rapid development of DC power transmission technology, HVDC gas insulated transmission lines (GIL) and gas insulated switchgear (GIS) are considered as potential alternative systems for future long-distance DC transmission. Therefore, extensive research and development are currently ongoing worldwide. SF6 has been widely used as a reliable insulating gas thanks to its excellent dielectric properties. However, due to its high global warming potential, other environmentally friendly alternative gas mixtures to replace the usage of SF6 have been found such as C4-Perfluoronitril (C4-PFN) and Trifluoroiodomethane (CF3I) based gas mixtures. A deep understanding of the behavior of the HVDC gas insulated systems using these alternative insulating gases is necessary to operate safely and economically. This means that partial discharge diagnosis under HVDC voltage application is very important. In this paper, the partial discharge inception voltage (PDIV) using 4% C4-Perfluoronitril (C4-PFN) / 96% CO2 and 30% Trifluoroiodomethane (CF3I) /70% CO2 gas mixtures are tested at different pressures ranging from 1 bar to 5 bar under both positive and negative DC voltage with electrode arrangement of different shapes and different gap distances. The current work will be further expanded as part of an extensive future research program.