Technical description
2 Protection functions
2.10 Directional earth fault protection
I0φ> (67N)
VM259.EN007
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85
2.10.
Directional earth fault protection
I
0φ
> (67N)
The directional earth fault protection is used for earth faults in
networks where a selective and sensitive earth fault protection
is needed and in applications with varying network structure
and length.
The device consists of versatile protection functions for earth
fault protection in various network types.
The function is sensitive to the fundamental frequency
component of the residual current and zero sequence voltage
and the phase angle between them. The attenuation of the
third harmonic is more than 60 dB. Whenever the size of I
0
and U
0
and the phase angle between I
0
and
U
0
fulfils the pick-
up criteria, the stage picks up and a start signal is issued. If
the fault situation remains on longer than the user's operation
time delay setting, a trip signal is issued.
Polarization
The negative zero sequence voltage
U
0
is used for polarization
i.e. the angle reference for I
0
. This
U
0
voltage is calculated
from the phase voltages internally. Since residual voltage is
calculated from the phase voltages, therefore any separate zero
sequence voltage transformers are not needed. The setting
values are relative to the configured voltage transformer (VT)
voltage/
3.