Characteristics of Series and Parallel Low Current Arc Faults in the Time and Frequency Domain

In low voltage switchgear there are two possible kinds of arc faults. Parallel arc faults occur between two phases, or phase and ground, and are often a result of degrading insulation or contamination. Series arc faults may be a result of loosening screw rivet connections in the busbar. Both types of arc faults can cause serious damage to the switchgear or even lead to a major arc fault resulting in short circuit. To be able to develop devices which can detect such low current arc faults, it is necessary to understand the behavior and special characteristics of low current arc faults. Several measurements were done to gain unique data of arc faults and normal load current from field measurements and lab setups. Both kinds of faults, serial and parallel, were analyzed in the time and frequency domains and then compared to an undisturbed load current. Several characteristics in the arc current could be extracted. Fourier analysis showed that certain ranges in the frequency spectrum can be used as an indication of an arc fault. Due to these analyses it is now possible to detect an arc fault by measuring the load currents in the switchgear.