Measurement of gas density recovery of a post-spark channel in a 1.0m air gap

The insulation recovery property of long air gaps is crucial for the relay protection setting of HVDC system. To investigate the relaxation process of a post-spark channel, a time-resolved moiré deflectometry technique was established in this paper. The spatial resolution and temporal resolution of this system are
$28.87\mu \mathrm{m}/\text{pixel}$
and 1µs, respectively. The gas temperature and gas density changes of a post-spark channel in a 1.0m air gap are obtained. It is found that the gas density in the post-spark channel increases exponentially with time. Since the air pressure in the post-spark channel stays at 1.0 bar approximately, the recovery characteristics of gas temperature is derived by using the state equation of ideal gas. Finally two different patterns in the relaxation process of the post-spark channel are found, and the calculated temperature is compared with the experimental results.