Siemens SIPROTEC 4, User Manual

Page: 139 / 734

Ferraris- disk, and the time response is adapted. This ensures a proper simulation of the temperature rise of
the protected object even for extremely fluctuating unbalanced load values. Reset begins as soon as 90 % of
the setting value is reached, in accordance with the dropout curve of the selected characteristic. In the range
between the dropout value (95 % of the pickup value) and 90 % of the setting value, the incrementing and
decrementing process is in idle state.
Disk emulation offers advantages when the behavior of the negative sequence protection must be coordi-
nated with other relays in the system based on electromagnetic measuring principles.
Logic
The following figure shows the logic diagram for the negative sequence protection function. The protection
may be blocked via a binary input. This resets pickup and time elements and clears measured values.
When the negative sequence protection criteria are no longer satisfied (i.e. all phase currents below 0.05 x
Ι
Nom
or at least one phase current is greater than 10 x
Ι
Nom
) all pickups issued by the negative sequence protec-
tion function are reset.
[7sj80-schieflastschutz-20060109, 1, en_US]
Figure 2-54 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
Functions
2.7 Negative Sequence Protection 46
SIPROTEC 4, 7SJ62/64, Manual 139
C53000-G1140-C207-8, Edition 08.2016