Superior characteristics of SF6 gas have enabled its successful use as the interruption media in high voltage circuit breakers. Unique combination of physical properties considers high dielectric strength, high thermal interruption capability and high heat transfer performance. However, having in mind its high global warming potential (GWP), long term use of SF6 gas in the future should be called into question. Considering that CO2 has much lower GWP than the SF6, it represents a promising alternative, but still with known inferior breaking performance. Therefore, careful investigation of the CO2 gas behavior should be obtained. In the present work, pressure rise in a high voltage circuit breaker during no-load operation has been simulated and measured for SF6 and CO2 gas, followed with the results comparison. For simulation of high voltage circuit breakers operation, computer program HV CB Simulation, which takes into consideration interaction between the interrupting unit and the driving mechanism is used. Thermodynamic properties of gases are calculated using highly accurate equations of state explicit in Helmholtz free energy.

Interruption of short circuit currents in high voltage circuit breakers requires high SF6 gas pressure, which can be generated by compression of SF6 gas and/or energy transfer from the arc. The pressure difference between circuit breaker chambers causes SF6 gas flow. The rise of pressure in the chambers is highly dependent on the design of the circuit breaker. This paper presents a universal approach to modeling of gas flow and pressure rise, which is based on a real gas model and implemented into computer software for high voltage circuit breaker interruption simulation. The approach allows simulation of SF6 and alternative media circuit breakers with any number of chambers and different types of valves and connections between chambers. The calculated pressure rise is validated by comparison with experimental measurement results from high power laboratory.