Siemens 7SC80 Manual page 82

Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
Switching to the lower pickup value or decreasing the pickup threshold is carried out phase-selectively. The
assignment of voltages to current-carrying phases is shown in the following table.
Table 2-3
Current
Ι
A
Ι
B
Ι
C
In order to avoid unwanted operation in case of a voltage transformer fault, function blocking is implemented
via a binary input controlled by the voltage transformer protection breaker as well as via the device-internal
voltage transformer monitoring.
The following two figures show the logic diagrams for the inverse time overcurrent protection with under-
voltage consideration.
82
Controlling voltages in relation to the fault currents
Voltage
V – V
A B
V – V
B C
V – V
C A
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017