2.17 Undervoltage and Overvoltage Protection (optional)
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7SD5 Manual
C53000-G1176-C169-1
behaviour of the undervoltage protection when the line is deenergized. While the
voltage usually remains present or reappears at the busbar side after a trip command
and opening of the circuit breaker, it is switched on at the outgoing side. For the und-
ervoltage protection this results in a pickup state being present if the voltage trans-
formers are on the outgoing side. If this pickup must be reset, the current can be used
as an additional criterion (current supervision CURR.SUP. Uphe<) to achieve this
result. Undervoltage will then only be detected if, together with the undervoltage con-
dition, the minimum current PoleOpenCurrent of the corresponding phase is also
exceeded. This condition is communicated by the central function control of the
device.
The undervoltage protection phase–earth can be blocked via a binary input „Uph-
e<(<) BLK“. The stages of the undervoltage protection are then automatically
blocked if a voltage failure is detected („Fuse–Failure–Monitor“, also see Section
2.22.1) or if the trip of the mcb of the voltage transformers is indicated (internal block-
ing) via the binary input „>FAIL:Feeder VT“.
Also during a single-pole automatic reclose dead time (using the internal autoreclo-
sure function) the stages of the undervoltage protection are automatically blocked in
the pole open state. If necessary, the current criterion will be considered, so that they
do not respond to the undervoltage of the disconnected phase when voltage trans-
formers are located on the outgoing side.
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