2.11 Undervoltage and Overvoltage Protection (optional)
159
7SD610 Manual
C53000-G1176-C145-4
Figure 2-58 Logic diagram of the undervoltage protection for phase voltages
Phase-phase und-
ervoltage
Basically, the phase-phase undervoltage protection operates like the phase-earth pro-
tection except that it detects phase-to-phase voltages. Accordingly, both phases are
indicated during pickup of an undervoltage stage if one of the stage thresholds Uph-
ph< or Uph-ph<< was undershot. Beyond this, Figure 2-58 applies in principle.
It is sufficient for the current criterion that current flow is detected in one of the involved
phases.
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