Prediction of critical dielectric strength of hot CF4 gas in the temperature range of 300-3500 K


Sulfur hexafluoride (SF6) gas has a quite high global warming potential and hence it is required that applying any substitute for SF6 gas. Much interest in fluorine-containing compounds appears due to their widespread use as gaseous candidate of SF6 in fault current interruption process considering its relatively high performance of dielectric insulation and arc quenching. The critical reduced electric field strengths of hot CF4 gas corresponding to the dielectric recovery phase of a high voltage circuit breaker are calculated in the temperature range from 300 to 3500 K. The equilibrium compositions of hot CF4 gas at various pressures were determined based on Gibbs free energy minimization. Additionally, adopting full sets of improved cross sections, the critical reduced electric field strength of this derived composition was obtained by a balancing electron generation and loss modeled by the interactions between electrons and the dissociated species of hot gas evaluated by the electron energy distribution function (EEDF) derived from the Boltzmann transport equation. In order to confirm the validity of the present calculation, the predicted result for hot CF4 gas was compared with experimental results and previous calculations and there exists a generally good agreement. We have presented that the dielectric strength of hot CF4 gas experiences a fast reduction as the continuous dissociation occurs with increasing temperature. Comparison with dielectric properties of hot SF6, regardless of reduced dielectric properties in the low temperature range, replacing SF6 with CF4 brings an increase of the critical reduced electric field strength for temperatures above 2200 K, indicating possible theoretical verification of the practical applications that CF4 is an admixture to SF6 gas as the arc extinguishing and insulation medium in high voltage circuit breakers.

IEEE Transactions on Dielectrics and Electrical Insulation