Evaluation of UHF Partial Discharge Measurements for SF6 and 20% C3F7CN / 80% CO2 Gas Mixture

Sulphur hexafluoride (SF6), the most commonly used dielectric medium in gas insulated equipment, has an extremely high environmental impact. The power industry, being the main user, has been looking for a replacement gas in order to minimize carbon emissions arising from high voltage equipment. C3F7CN is considered as a potential SF6-alternative. A mixture of 20% C3F7CN and 80% CO2 has shown to have a comparable breakdown performance to SF6 under uniform field. However, partial discharge (PD) characteristics of the 20% C3F7CN / 80% CO2 gas mixture in comparison to SF6 have yet to be extensively studied. This paper investigates the partial discharge inception voltage (PDIV) and extinction voltage (PDEV) of the aforementioned gases under highly divergent fields. PDIV and PDEV values for both gases were found to increase with pressure but SF6 demonstrated higher PDIV and PDEV than the 20% C3F7CN / 80% CO2 gas mixture. A difference in the growth rate of PDs between SF6 and 20% C3F7CN / 80% CO2 has also been identified with the