Very intensive and extensive dry band arching plus a
flashover of a single disk in one case (Fig. 11) was detected
on pre wetted naturally contaminated glass insulators.
Leakage current change of a pre wetted contaminated glass
insulator in timeline is seen in Fig. 8. At first, when the
phase voltage is applied to the insulator as seen in Fig. 8 the
leakage current of an insulator begins to decrease. While
decreasing, it will start to increase again in some point, after
some time of increase it starts to decrease again. This
temporal increase of leakage current of a drying insulator
string is caused by partial discharges, dry band arching and
flashovers of single disks in string that are partly shortcircuiting
string’s creepage distance and thereby increasing
leakage current. Increase rates of the leakage currents did
not turn out to be high enough (i.e. the total remaining
conductivity of non-short circuited path of insulator’s
creepage distance was not high enough to feed the arc to
develop flashover) to cause dry band arching to develop
arcing of the entire string.