Risk assessment basis of moving particles in gas insulated substations

Comprehensive acoustic measurements on bouncing particles in a gas insulated substation (GIS) have been carried out. The objective is to find parameters that both are available from external acoustic measurements and usable for assessing whether a particle has the potential to cause an insulation breakdown. The elapsed time between subsequent particle impacts is a measure of how far into the high-field region the particle can move, and thus also a measure on criticality. Secondly, the amplitude of the acoustic signal generated as a particle imparts the enclosure increases with increasing particle length and thus also with increasing criticality. Moreover, plotting these two parameters against each other ('particle flight time' vs. 'signal amplitude at impact') for a significant number of impacts (e.g. 1000) always yields a very characteristic pattern, which in itself is a strong indication that the recorded signals are generated by one moving particle.