The Effect of Gas Dynamics and Properties of SF6 and Air on Short Line Fault Interruption

This paper covers the derivation of a short line fault equation for the maximum rate of rise of recovery voltage (RRRV) characteristic of gas blast interrupters. It is shown that the maximum RRRV is 1) approximately proportional to the gas pressure; 2) proportional to the effective nozzle arc length at current zero and the number of series breaks, 3) inversely proportional to the 3/2 power of the rate of change of current, and 4) proportional to a coefficient that is a function of gas properties. Based on assumptions concerning air and sulfur hexafluoride (SF6) arc temperatures, the equation indicates the superior interrupting ability of SF6 for identical conditions of pressure, current, and interrupter assembly.