Ionization and Breakdown Characteristics of Hexafluoro-2-butyne and Its Mixture With N₂

To evaluate the feasibility of using hexafluoro- 2-butyne (C₄F₆) as a substitute for SF₆ gas in gas insulated power equipment, the ionization and breakdown characteristics of C₄F₆ pure gas and C₄F₆/N₂ mixtures are studied. The reduced ionization coefficient, reduced attachment coefficient, and critical reduced field strength (E/N)_lim of C₄F₆ and C₄F₆/N₂ mixtures in the range of 200 to 800 Td (1 Td=10⁻²¹ V⋅m²) are measured through steady-state Townsend(SST) test, and their insulation performance and stability are evaluated through breakdown discharge test under power frequency voltages. The results show that the (E/N)_lim of C₄F₆ gas is 697.7 Td, which is 1.96 times that of SF₆. The (E/N)_lim of C₄F₆/N₂ mixture shows a linear growth pattern with the increase of C₄F₆ molar ratio, and there is no synergistic effect between C₄F₆ and N₂. The (E/N)_lim value of 34.0% C₄F₆/66% N₂ mixture is equivalent to SF₆. The insulation strength of 25% C₄F₆/75% N₂ under 0.5 MPa is 0.89 compared to SF₆ under the same pressure. After the breakdown test, a large number of solid decomposition products are generated on the electrode surface, indicating poor stability of C₄F₆ gas. Taking into account insulation performance and stability, C₄F₆ and its mixture are difficult to be applied as insulation media in gas insulated equipment.