ABB REG316 4 Series Operating Instructions Manual page 130

ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
Response after decay of the memorised voltage
The voltage measured by the protection can quickly decay to
almost zero for a close fault and make determining direction un-
reliable. For this reason, the function includes a voltage memory
feature and for the first 200 milliseconds after the incidence of an
overcurrent, the voltage measured immediately before the fault
is used as reference to determine fault direction.
After this time, the last valid direction is used for an adjustable
period (see next paragraph).
"MemDirMode" provides facility for setting how the protection
must respond after this time or in the event that the circuit-
breaker is closed onto a fault and no voltage could be memo-
rised beforehand. The two possible settings are the protection
can trip or it can block.
Time during which the memorised direction is valid
The "MemDuration" setting determines how long the last valid di-
rection measurement shall be used. The setting should be as
short as possible (200 ms) when the function is being used as
backup for a distance function in an HV power system, because
an actually measured voltage is only available during this time
and therefore it is only possible to detect a reversal of direction
during this time. For longer settings, the last valid power direc-
tion is used instead of the actually memorised voltage.
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