Due to its superior insulating qualities

perfluoroisobutyronitrile (C4F7N) mixed gas is commonly recognized as an environmentally friendly alternative to SF6. However

in comparison to SF6

there is still a gap in arc interrupting ability. For the purpose of guiding the development of environmentally friendly switchgear

it is crucial to investigate the interrupting performance of C4F7N mixed gas under various oxygen (O2) ratios. In order to analyze the gas arc combustion process of 0.6 MPa SF6

0.8 MPa 6% C4F7N/CO2

6% C4F7N/CO2/10%O2

and 6% C4F7N/CO2/20% O2

we established a 2-D arc magnetohydrodynamic model for the extinguishing chamber of a 126 kV circuit breaker (CB)

and also compared the temperature distribution and airflow variation of the arc in the C4F7N mixed gas extinguishing chamber under various O2 ratios. The Mayr arc model was used to study the effect of O2 ratio in C4F7N mixed gas on the post-arc thermal interrupting performance of CB. The results show that an increase in the proportion of O2 in the C4F7N mixed gas will increase the temperature of the C4F7N mixed gas arc core

decrease the arc radius

expand the radial temperature distribution gradient of the arc

increase the upstream gas pressure of the CB nozzle

and accelerate the gas axial blowing speed. For interrupting 25 kA short-circuit currents

the critical recovery voltage rise rates (RRRV) of CB with 0.6 MPa SF6 and 0.8 MPa C4F7N mixed gas with O2 ratios of 0%

10%

and 20% are 3.0

1.0

1.21

and 1.235 kV/μs

respectively. The post arc thermal interrupting capacity of C4F7N mixed gas CB has increased with an increase in O2 proportion. At 20% O2 proportion

the thermal interrupting ability of C4F7N mixed gas reaches 41.1% of SF6

7.8% greater than that of 6% C4F7N/CO2. The relevant research provides theoretical guidance for promoting the development of environmentally friendly C4F7N mixed gas high-voltage switchgear.