Rockwell Automation 865 Differential Protection Relay - Manual (Page 61)

Protection Functions 3-17
865-UM001A-EN-P – July 2009
Recorded Values of the Latest Eight Faults
Detailed information is available on the eight latest faults: Time
stamp, unbalance current, elapsed delay and setting group.
Table 3.10 – Parameters of the Current Unbalance Stage (8 latest faults) I 2 >, I’ 2 > (46)
Parameter Value Unit Description
yyyy-mm-dd Time stamp of the recording, date
hh:mm:ss.ms Time stamp, time of day
Flt %In Maximum unbalance current
EDly % Elapsed time of the operating time setting.
100% = trip
SetGrp 1
2 Active setting group during the fault
Undirectional earth fault protection is used for 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 3.12 – Typical block diagram of the earth fault stage I 0 >
Figure 3.13 – Typical block diagram of the earth fault stages I 0 >>, I 0 >>> and I 0 >>>>
Earth fault protection
I
0
> (50N/51N)