Measurements and simulation of the dielectric recovery in a SF6 circuit breaker

Measurements of the dielectric recovery after interruption of currents of a few kA peak were carried out on a modified SF₆ gas circuit breaker (GCB) at different strokes and in a time range between 50 ¿s and few milliseconds after current zero (CZ). The GCB has been adapted to increase the dielectric stress at the plug and to allow optical observation of the plug region during the recovery. Two different nozzle arrangements were tested. Movies of the arc close to current zero and of the successive breakdown are recorded using a high speed video camera to gain information on the BD location and the arc structure. The measured recovery characteristic is compared to predictions resulting from computational fluid dynamics (CFD) simulations coupled with capacitive electric field calculations. The comparison shows a reasonable qualitative agreement, although the measured recovery is faster than the predicted one. Possible reasons for this discrepancy are discussed.