Megger SMART THUMP ST16, User Manual

Page: 39 / 62

How to Perform a Test
AVTMST16 Rev 1 May 2016
29
Current Decoupling (ICE)
As an alternative way for pre-location of high resistance faults, the SMART
THUMP provides the current decoupling method (ICE, Surge Pulse).
The capacitive discharge of the surge capacitor via the surge switch triggers and
ignites the fault and causes it to a flash over. This flashover results in a travelling
wave current on the HV return, which is inductively de-coupled and shown on
the Reflectometer as a transient. Subsequently, an attenuated transient wave
travels back and forth between fault and surge generator (standing wave)
By decoupling the current signal from the HV return, an oscillation is obtained
where the period length corresponds directly to the fault distance.
Note: Fault distance includes length of HV output cable: deduct this length to
get the distance to the fault going forward from the connection point, e.g.
transformer, switchgear etc.
Proceed as follows to pre-locate the cable 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 charge the capacitor (only if Automatic High Voltage Release is disabled).
See page 20.
Result: The capacitor is charged up to 16 kV.
5
Select to discharge the capacitor (only if Automatic High Voltage Release is
disabled). See page 20.
Result: A sudden capacitor discharge (shot) is initiated.
If a voltage breakdown takes place, a red oscillating curve is shown in the display.
NOTE: If no trigger is received and, thus, no fault trace is shown, you may
try to repeat the procedure with a higher surge voltage (if possible) by
selecting the
menu item.