Side 7 of 16
Userguide CableTroll 210 March 2020
01021000/11/12/13
The following simplified formula may be used to estimate the capacitive discharge current of a line:
Ic = U * La + U * Lc
300 K
Ic = Capacitive current in A
U = Nominal voltage in kV
La = Overhead line length in km
Lc = Cable length in km
K = 10 for oil impregnated cables
5 for PEX cables
3 for PVC cables
In order to avoid that the CableTroll 210 is activated by an earth fault downstream of the indicator, the
following criterion must be met.
Ic < It
where
Ic = capacitive current down-stream of the indicator.
It = CableTroll 210 programmed trip-level sensitivity.
To estimate the capacitive discharge current at any line point, you must calculate the contribution from
all the overhead lines and underground cables lengths only beyond (down-stream) that point.
Figure 3. Capacitive discharge current calculation example
The indicator will start to flash when a current exceeding the programmed overcurrent threshold occurs.
3.3 Earth fault detection
When the vectoral sum of the cable currents exceeds the trip level setting. (With no earth fault this sum
is close to zero). Both transient and permanent faults are treated in the same way.
