Megger SG32-1500M, User Manual

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M
SG32-UG-EN-V01 Dec 2016
8
Differential Arc Reflection (DART)
In Differential Arc Reflection mode unwanted and confusing reflections are
removed leaving a clean trace with only the fault position being displayed by a
positive pulse (HV trace is mathematically subtracted from LV trace). This method
can be helpful in locating high-resistance faults in complex cable systems;
however it is important to recognize that the fault reflection is positive in this
mode.
ICE (Impulse Current, Surge Pulse or Current Decoupling)
ICE is a good alternative if the ARC Reflection method does not provide reliable
fault distances on e.g. long-, wet- or PILC cables. The fault is ignited and the
resultant transients are recorded on the TDR, which in this mode acts as a
transient recorder (no active TDR pulse). The trace displays negative reflections
both at the point of fault (low impedance) and also where the surge generator is
connected to the cable. The first displayed reflection is indicative of the
“ionization delay” i.e. the time needed for the fault to flashover after the release
of the HV surge. The distance between 2 consecutive peaks of the transient
equals the distance to fault
minus
the length of the HV test lead. For added
accuracy more than one measurement at different voltages should be used.
Generally speaking the results are very comparable to those found with the ARM
method on longer cables; they could be slightly off on short cables.