2.7 Directional earth fault
protection I0φ> (67N)
2 Protection functions
Technical description
56
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VM59.EN001
2.7.
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
Zero sequence voltage
U
0
is used for polarization i.e. the angle
reference for I
0
. The U
0
voltage is measured via energizing
input U
0
:
3LN+U
0
: The zero sequence voltage is measured with
voltage transformer(s) for example using a broken delta
connection. The setting values are relative to the VT
0
secondary voltage defined in configuration.
NOTE! The U
0
signal must be connected according the connection diagram
(Figure 8.8.1-1) in order to get a correct polarization.