Functions
2.6 Negative Sequence Protection 46
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
114
Figure 2-32 Logic diagram of the unbalanced load protection
The pickup of the definite time overcurrent protection can be stabilized by the configured dropout time 4012
46 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. Should the threshold value be exceeded after its
expiry, the trip command is issued immediately. If the threshold value is not exceeded at this time, there will be
no reaction. If the threshold value is exceeded again after expiry of the trip-command delay time, while the
dropout delay time is still running, tripping occurs immediately.
The configured dropout times do not influence the tripping times of the inverse time elements as these depend
dynamically on the measured current value. For purposes of dropout coordination, disc emulation is used with
electro-mechanical relays.
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