Voltage-Dependent Current Fault Detection U/I - Siemens siprotec 7SA6 User Manual

Functions
6.2.2.2

Voltage-Dependent Current Fault Detection U/I

Mode of Operation
and Characteristic
6-32
parameter SK )$8/76 (address $) according to Table 6-2. In the non-earthed
network, the phase–to–phase loop is always selected for single–phase pick-up
without earth-fault detection.
The phases that have picked-up are signalled. If an earth fault has been detected, it
is also indicated. Pick-up will drop off if the signal falls below 95 % of the pick-up value.
Table 6-2 Loop and phase indication for single–phase overcurrent pick-up
Pick-up Earth-fault de-
module tection
L1
L2
L3
L1
L2
L3
L1 yes
L2 yes
L3 yes
1
) Only possible in earthed networks
The U/I pick-up is a per phase and per loop pick-up mode. Here the phase currents
must exceed a threshold , while the threshold value depends on the magnitude of the
loop voltage.
Pick-up due to earth faults in systems with a non-earthed system star point is
effectively suppressed by means of the measures described in Section 6.2.1.
The basic characteristics of the U/I pick-up can be seen from the current–voltage
characteristic shown in Figure 6-19. The first requirement for every phase pick-up is
that of the minimum current ,SK! is exceeded. For the evaluation of phase–phase
loops both relevant phase currents have to exceed this value. Above this current the
current pick-up is voltage-dependent with the slope being determined by the settings
U(I>) and U(I>>). For short-circuits with large currents the overcurrent pick-up ,SK!!
(Section 6.2.2.1) is superimposed. The bold dots in Figure 6-19 designate the settings
which determine the geometry of the current/voltage characteristic.
Loop pick-up will drop off if the signal falls below 95 % of the relevant current value or
exceeds 105 % of the relevant voltage value.
Parameter
3K )$8/76
no
no phase–phase
no
no
no phase–earth
no
any
Valid
loop
L3–L1
L1–L2
L2–L3
L1–E
1
) L2–E
L3–E
L1–E
L2–E
L3–E
C53000-G1176-C133-1
Signalled
phase(s)
L1, L3
L1, L2
L2, L3
L1
L2
L3
L1, E
L2, E
L3, E
7SA6 Manual