A blast pressure analysis program for gas circuit breaker taking ablation, arc energy and decomposition effect into consideration was developed. In general, it is well known that SF₆ gas accompanies dissociation and ionization in high temperature region, so we cannot apply the equation of state of ideal gas to high temperature region. Thus, it is necessary that the rate of specific heat, specific heat at constant pressure and gas constant are dealt with functions of gas pressure and temperature when SF₆ arc and/or high temperature SF₆ gas calculates.
In this paper, first, we evaluated the decomposition gas model by comparing Pressure-Temperature (P-T) characteristic calculated by the decomposition gas model with P-T characteristic that derived by the summing partial pressures of all dissociated chemical species. Next, using its calculation method, we calculated pressure analysis in gas circuit breaker. Finally, we compared theoretical value was calculated by this program with experimental value tested in 145kV, 40kA class gas circuit breaker. As a result of this simulation, theoretical analysis agreed very well with experimental results.