Siemens SIPROTEC 4 7SJ61 Manual page 134

Functions
2.9 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
[7sj61-empf-erdfehlererfass-20090617, 1, en_US]
Figure 2-52
The pickup of the definite time overcurrent protection can be stabilized by the configurable dropout time
3121 50Ns T DROP-OUT. This time is started and maintains the pickup condition if the current falls below
the threshold. Therefore, the function does not drop out at high speed. The trip command delay time
continues running. After the dropout delay time has elapsed, the pickup is reported OFF and the trip delay
time is reset unless the threshold has been exceeded again. If the threshold is exceeded again during the
dropout delay time, the time is cancelled. The trip command delay time continues running. If the threshold
value is exceeded after its expiry, the trip command is issued immediately. If the threshold value is not
134
Logic diagram of the sensitive ground fault detection
SIPROTEC 4, 7SJ61, Manual
C53000-G1140-C210-6, Edition 05.2016