Siemens siprotec 7SD5 User Manual page 114

2 Functions
Table 2-4
1)
Voltage-Dependent The U/I pickup is a per phase and per loop pickup mode. Here the phase currents
Current Fault De- must exceed a threshold , while the threshold value depends on the magnitude of the
tection U/I loop voltage.
Pickup on earth faults is effectively suppressed in networks with non-earthed neutral
points by means of the measures described above in Section „Earth Fault Detection".
The basic characteristics of the U/I pickup can be seen from the current–voltage char-
acteristic shown in Figure 2-31. The first requirement for every phase pickup is that of
the minimum current Iph> is exceeded. For the evaluation of phase-phase loops,
both relevant phase currents have to exceed this value. Above this current, the current
pickup is voltage-dependent with the slope being determined by the settings U(I>)
and U(I>>). For short-circuits with large currents the overcurrent pickup Iph>> is su-
perimposed. The bold dots in Figure 2-31 mark the settings which determine the ge-
ometry of the current/voltage characteristic.
The phases that have picked up are signalled. The picked up loops are relevant for
processing the measured values.
Loop pickup will drop out if the signal falls below 95 % of the respective current value
or exceeds approx. 105 % of the respective voltage value.
Figure 2-31
114
Loops and phase indications for single-phase overcurrent pickup
Pickup Earth Fault
Module Detection
L1 No
L2 No
L3 No
L1 No
L2 No
L3 No
L1 Yes
L2 Yes
L3 Yes
only active for earthed power systems
U/I characteristic
Parameter Valid Loop
1ph FAULTS
L3-L1
phase-phase L1-L2
L2-L3
L1-E
1)
phase-earth L2-E
L3-E
L1-E
any L2-E
L3-E
Alarmed
Phase(s)
L1, L3
L1, L2
L2, L3
L1
L2
L3
L1, E
L2, E
L3, E
7SD5 Manual
C53000-G1176-C169-1