Megger SMART THUMP ST16, User Manual

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AVTMST16 Rev 1 May 2016
21
5
HOW TO PERFORM A TEST
Detecting and Locating a Cable Fault in a Shielded Medium
Voltage Power Cable
Locating a Faulty Cable Section (Sectionalizing)
Introduction
The sectionalizing technique is used to trouble shoot a distribution loop circuit in
order to identify the faulted section, so it can be quickly switched out, and the
rest of the circuit can be re-energized to provide service to all customers.
For this purpose, a LV reflection image is taken and scanned for impedance
changes which are related to the cable end and transformers. A second reflection
image of the TDR pulse is taken while an electrical arc is ignited by a sudden
discharge of the charged capacitor at the fault location. This reflection is
negative.
With both traces lying on top of each other, the fault location (position where
the two traces diverge from each other) is identified and the transformers
reflections provide the landmarks to identify the faulted cable segment. It will be
switched out by pulling the elbows to the left and right side of the fault. Service
to all customers is provided by closing the normally open point within the
distribution loop.
2 Alternatives
The procedure called “Sectionalizing” in the configuration set up will work flow
perform the following steps:
Pattern 1

low voltage TDR trace to identify cable end (blue trace)

low voltage trace to identify all transformers in the faulted (half) loop (blue
trace)

high voltage trace to identify fault (negative reflection in red trace)