Assessment on gas-polyethylene terephthalate solid interface partial discharge properties of C4F7N/CO2 gas mixture for eco-friendly gas insulating transformer

The eco-friendly insulating gas perfluoroisobutyronitrile (C₄F₇N) is potentially used in gas-insulated transformers (GIT) to replace sulphur hexafluoride (SF₆). However, evaluation of the long-term insulation reliability and gas–solid interface discharge decomposition characteristics of the gas–solid film insulation structure in GIT is indispensable. The authors simulated the gas–solid film insulation structure in GIT and explored the interface partial discharge (PD) characteristics of C₄F₇N/CO₂ gas mixture with polyethylene terephthalate (PET). The effect of gas pressure, mixing ratio on gas–solid interface gas decomposition, PET degradation was investigated, and the interaction mechanism was analysed. It is found that the interface PD generated three degradation regions on a PET film. The gas–solid interface reaction in the electrode contact region and the discharge development trace was significantly higher than that of halation region. The content of gas decomposition products decreases with the increase of gas pressure and the PD intensity of SF₆-PET is inferior to that of C₄F₇N/CO₂ under the same condition. Relevant results provide reference for the development and application of C₄F₇N/CO₂ based GIT.