Faults on EHV lines are generally single-phase-to-ground ones and not permanent in the majority of
cases. Thus single phase auto reclosure (SPAR), at which the faulty phases are tripped for a short time,
eliminates the predominant part of the faults [1,2]. The secondary arc, which follows the high power
arc after tripping the faulty phases at both side of the line may endanger the successfulness of
reclosing if the duration of the switched off interval (dead time) is not long enough to ensure the
extinction of the arc. The secondary arcing times recorded on different EHV lines or measured in
laboratory tests show significant spread, consequently, to select a dead time according to the longest
experimental secondary arc extinction time is not feasible.
During commissioning of the double circuit 420 kV interconnection between Hungary and Croatia
several staged faults were initiated to analyze the arc extinction performance. Initially the line was in
operation by connecting the two circuits in parallel along the 1/3rd of the full length. In this
configuration the longest secondary arc extinction time was 4 seconds and the secondary arc has not
extinguished in 27s in one of the tests, so the line had to be tripped out to clear the staged fault. Later
on, the length of the Croatian section of the line has been significantly shortened after putting a new
substation into service. The increased performance of SPAR of the new arrangement has been proved
with field tests.
A realistic representation of the secondary arcs is essential in determining the auto-reclosure
performance of EHV transmission lines. As shown in the paper, the random variation of the arc
parameters influences significantly the arc extinction time. The results of the field tests confirmed the
importance of the distributed nature of the transmission line and the nonlinear characteristic of the arc
resistance in the intermittent region of arcing, where temporary extinctions and sudden re-ignitions in
the arc channel produce transient wave processes along the line
