Experimental and calculation study on insulation strength of C4F7N/CO2 at low temperature

摘要

In this paper, the insulation strength of C4F7N/CO2 with temperature is obtained by AC breakdown tests and theoretical calculations. The experimental results with 9%C4F7N/91%CO2 at 0.7 and 0.5 MPa pressures show that the breakdown voltage changes nonlinearly with temperature. Theoretical analysis shows that the nonlinear change is caused by liquefaction of C4F7N. The critical electric field of C4F7N/CO2 is calculated based on the streamer discharge theory. A calculation model is established to calculate the usable pressure of C4F7N/CO2 and the mole fraction of C4F7N at given minimum temperature, which can provide reference for its practical application.