How to Perform a Test
AVTMST16 Rev 1 May 2016
31
How to Pinpoint the Fault (shielded MV power cable)
The thumping mode can be used to pinpoint a fault between two phase
conductors or between a phase conductor and the neutral conductor or on
unshielded cables between the phase conductor and earth ground..
The SMART THUMP serves as surge pulse generator to continuously feed high
voltage pulses into the defective cable, producing voltage flash-overs (arcing) at
the fault position. The fault can either be pinpointed using a magnetic / acoustic
coincidence detector for best results or a simple acoustic detector with distinct
and well understood limitations. The criterion for pinpointing with a simple
acoustic detector is the greatest loudness of the flash-over noise at the fault
location, or, in the case of a magnetic / acoustic coincidence measurement, the
smallest propagation time difference between speed of light and speed of sound,
where it is not the loudest sound, but the first after receiving the magnetic signal.
The latter one is more accurate and can be used in all high resistance fault
situations (e.g. Megger Digiphone Plus) and
even for locating faults in
conduit
.
Proceed as follows to pinpoint the fault:
Step Description
1
Select the
menu item from the main menu or from the
submenu (depends on the
system configuration).
2
Adjust the surge voltage and select
to confirm the value.
3
Press the green illuminated “HV ON” button
.
4
Select
to start the thumping mode (only if
Measurement Start
option is set to
Manual.
See page 18.
Result:
The capacitor is charged up and a discharge takes place after 5 seconds or, if the
charging takes longer, right after the selected surge voltage has been reached.
This process is then repeated until thumping is manually stopped.
If required, you can adjust the surge voltage by selecting the
menu item.
5
Pinpoint the fault within the pre-located area with a surge wave receiver like the Megger
Digiphone Plus.
For detailed instructions, please refer to the user manual of the surge wave receiver.
6
Select
to stop thumping.
Summary of Contents for SMART THUMP ST16
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