Feasibility Study of Using C4F7N/Helium in Eco-friendly Gas-insulated Transformer: Dielectric Strength and Heat Dissipation Performance

This contribution proposes an eco-friendly insulation gas mixture of perfluoroisobutyronitrile (C₄F₇N) /helium with good heat transfer performance for gas-insulated transformers (GITs). The dielectric strength of C₄F₇N/helium was assessed by AC breakdown test and voltage withstand test. The heat dissipation performance of the mixture was evaluated by test of temperature rise due to short-circuit on a self-cooling GIT. The test results demonstrated that the dielectric strength of C₄F₇N/helium exhibited a synergistic effect in various proportions. Especially for 40% C₄F₇N /60% helium, its dielectric strength could exceed that of SF₆ used in existing GITs. After filling it into the eco-friendly GIT, the dielectric strength remains stable and the average temperature rise of the winding could be reduced by over 20%. In addition, based on the convection heat dissipation model, a calculation method for the average temperature rise of the eco-friendly GIT was adjusted. The errors of the model were found to be within a margin of ±3°C for C₄F₇N/helium under different pressures and proportions. The dielectric strength and heat dissipation performance of the mixture indicated that 40% C₄F₇N /60% helium could directly replace SF₆ without adjusting voltage levels or insulation gaps in larger capacity and eco-friendly GITs.