Study on Dispersion of Impulse Discharge in SF 6 and Eco-Friendly Insulating Gas C 4 F 7 N/CO 2

In recent years, C 4 F 7 N/CO 2 gas has been widely studied as an eco-friendly alternative to SF 6 , which is commonly used in electrical equipment. To ensure electrical equipment reliability, the dispersion of impulse discharge voltage of insulated gas is generally required to be less than 3%. However, experimental results indicate that under fault conditions, such as sudden pressure changes or electric field distortion, the discharge dispersion of both C 4 F 7 N/CO 2 and SF 6 often exceeds 3%. This paper investigates the impact of pressure and electric field nonuniformity on the dispersion of impulse discharge voltage for conventional and eco-friendly insulating gases under varying degrees of electric field nonuniformity. Experiments reveal that under identical conditions, the 9%C 4 F 7 N/91%CO 2 mixture exhibits lower impulse discharge voltage dispersion compared with SF6. As pressure increases, the dispersion decreases for both gases. Conversely, dispersion increases with higher electric field nonuniformity, and the 9%C 4 F 7 N/91%CO 2 mixture demonstrates greater sensitivity to electric field nonuniformity than SF 6 . In practical applications, electrical equipment typically operates under slightly nonuniform electric fields and high pressure, meeting dispersion requirements. However, if electric field distortion causes the nonuniformity factor ( f ) to exceed 2.4 or if pressure drops below 0.3 MPa then dispersion increases significantly, reducing the reliability of insulation performance data.