Technical Manual WIC1 SEG Electronics GmbH
DOK-TD-WIC1E, Rev. M 49
6.8 Special features for earth current tests
Functional description:
In the WIC1 the earth current is calculated and cannot be measured. It is established from the geometrical amount
of the three phase current values, more or less a numerical Holmgreen. If, for instant, a single-phase test current is
impressed, the measuring value (tripping value) in the earth current path equals the current in the tested phase. If,
with a phase shift of 120° a three-phase test current is impressed, the measuring value in the earth current path
equals zero.
Requirement on the test system:
The WIC1 is powered by the instrument transformer. In order to guarantee reliable tripping a minimal current of
0.9 x lowest nominal CT current (0.9 x lowest I> setting) has to flow in one of the phases. If the setting of the earth
current IE> is lower than the smallest possible switching point for the phase current, then the switching point for
earth current tripping can only be tested by a three-phase power source. In case the set switching point for earth
current is higher than the smallest possible switching point for overcurrent tripping (Is x I>, then the test can be per-
formed with a single-phase power source.
6.8.1 Switching points for the earth current step
Table 6.5: Test current via the CD winding with the IE> step and the different Is setting values
** When the earth current setting is <0.9 x Is a three-phase test system has to be used for correct testing. With a
single-phase test the trip is only triggered from 0.9 x Is on.