ABB REO 517 Applications Manual page 157

&KDSWHU 
Sudden voltage change function (SVC)
9ROWDJH
The setting of the opening delay t of the voltage reduction measuring element must be
greater than the delay of the zone 2 and zone 3 elements plus a margin for the respective
zones to give a tripping pulse.
However, note that the time must be shorter than any down stream units with any re-
closing.
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