2.11 Earth fault protection I0>
(50N/51N)
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Recorded values of the latest eight faults
There is detailed information available of the eight latest earth
faults: Time stamp, fault current, elapsed delay and setting
group.
Recorded values of the directional earth fault stages (8 latest
faults) I
0
>, I
0
>> (67N)
Time stamp of the recording, date
Maximum earth fault current
Elapsed time of the operating time
setting. 100% = trip
Fault angle of I
0
. –U
0
= 0
Max. U
0
voltage during the fault
Active setting group during fault
2.11. Earth fault protection I
0
> (50N/51N)
Undirectional earth fault protection is used to detect earth
faults in low impedance earthed networks. In high impedance
earthed networks, compensated networks and isolated
networks undirectional earth fault can be used as back-up
protection.
The undirectional earth fault function is sensitive to the
fundamental frequency component of the residual current 3I
0
.
The attenuation of the third harmonic is more than 60 dB.
Whenever this fundamental value exceeds the user's pick-up
setting of a particular stage, this 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.
Figure 2.11-1. Block diagram of the earth fault stage I
0
>
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