Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
67
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
Nom
.
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.
These elements can be blocked by the automatic reclosing feature (79 AR).
The following figures show the logic diagrams for the current elements 50-1 and 50N-1.
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