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 Controlling voltages in relation to the fault currents
Current Voltage
Ι
A
V
A
– V
B
Ι
B
V
B
– V
C
Ι
C
V
C
– V
A
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.
Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
82 SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
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