Optical Investigation of a Spark Gap for DC Protection around Current Zero

The applied experimental setup consists of a pair of fixed electrodes forming a short gap in air. The electrodes are connected with a thyristor forming a parallel current path. Once the thought flashover ignited arc has burnt a given time in the range of several hundreds of microseconds, the thyristor will be fired causing a commutation of the current in the semiconductor path. Hence, the current through the electrode gap will be reduced. The extinguishment of the arc permits the creation of a current zero in the gap. The focus of the experimental work is set to the analysis of the arc plasma during the DC phase and its distinction in the current extinction phase (current zero). High speed camera observation and optical emission spectroscopy are carried out and combined with the electrical measurements.