Siemens SIPROTEC, Руководство пользователя

Страница: 120 / 776

Functions
2.5 Distance Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
120
Voltage dependent current pickup U/
I
The U/
I
pickup is a per phase and per loop pickup mode. Here the phase currents must exceed a threshold,
while the threshold value depends on the magnitude of the 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 characteristic shown in Figure
2-41. The first requirement for every phase pickup is that the minimum current Iph> is exceeded. For the eval-
uation of phase-to-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 setting parameters
U(
I
>) and
U(
I
>>) . For short-circuits with large currents the overcurrent pickup Iph>> is superimposed. The bold dots in
Figure 2-41 mark the setting parameters which determine the geometry 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 2-41 U/
I
characteristic