Siemens SIPROTEC 7SJ62 Manual page 74

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 2-2
Current
I
A
I
B
I
C
In order to avoid an unwanted operation in case of a voltage transformer fault, a function blocking is implement-
ed via a binary input controlled by the voltage transformer protection breaker as well as via the device-internal
measuring voltage failure detection ("Fuse Failure Monitor").
The following two figures show the logic diagrams for the inverse time overcurrent protection with undervoltage
consideration.
74
Controlling voltages in relation to the fault currents
Voltage
V – V
A B
V – V
B C
V – V
C A
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008