Definite Time Overcurrent Elements 50-1, 50N-1 - Siemens SIPROTEC 7SK80 Manual
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2.2 Overcurrent Protection 50, 51, 50N, 51N
2.2.3
Definite Time Overcurrent Elements 50-1, 50N-1
For each Element an individual pickup value 50-1 PICKUP or 50N-1 PICKUP is set. Apart from
Fundamental, the True RMS can also be measured. Each phase and ground current is compared separately
with the setting value 50-1 or 50N-1 for each Element. If the respective value is exceeded, this is signaled. If
the inrush restraint feature (see below) is applied, either the normal pickup signals or the corresponding inrush
signals are output as long as inrush current is detected. After user-configured time delays 50-1 DELAY or
50N-1 DELAY have elapsed, a trip signal is issued if no inrush current is detected or inrush restraint is dis-
abled. If the inrush restraint feature is enabled and an inrush condition exists, no tripping takes place but a
message is recorded and displayed indicating when the overcurrent element time delay elapses. Trip signals
and signals on the expiration of time delay are available separately for each Element. The dropout value is ap-
proxmiately 95% of the pickup value for currents > 0.3 I
Pickup can be stabilized by setting dropout times 1215 50 T DROP-OUT or 1315 50N 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 50-1 DELAY or 50N-1 DELAY continues
running in the meantime. After the dropout delay time has elapsed, the pickup is reported OFF and the trip delay
time is reset unless the threshold 50-1 or 50N-1 has been exceeded again. If the threshold is exceeded again
during the dropout delay time, the time is cancelled. However, the trip-command delay time 50-1 DELAY or
50N-1 DELAY continues running. If the threshold value is exceeded after its expiry, the trip command is issued
immediately. If the threshold value is not exceeded at this time, there is 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, trip-
ping occurs immediately.
Pickup stabilization of the overcurrent elements 50-1 or 50N-1 by means of settable dropout time is deactivated
if an inrush pickup is present since an inrush does not represent an intermittent fault.
The pickup values of each 50-1 Element for phase currents and 50N-1 Element for the ground current and the
element-specific time delays can be set individually.
The following figures show the logic diagrams for the current elements 50-1 and 50N-1.
58
.
Nom
E50417-G1140-C344-A4, Release date 08.2010
SIPROTEC, 7SK80, Manual
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