9440300990 10-3
DECS-250 Protection
Figure 10-3. Overexcitation Protection Settings
Generator Undervoltage
An undervoltage pickup condition occurs when the sensed generator terminal voltage decreases below
the pickup setting. An undervoltage trip condition occurs if the generator voltage remains below the
pickup threshold for the duration of the time delay setting. Generator undervoltage protection can be
enabled and disabled without altering the pickup and time delay settings. Undervoltage pickup and trip
elements in BESTlogicPlus can be used in a logic scheme to initiate corrective action in response to the
condition.
Settings that are related to machine ratings can be set in either actual units of voltage or in per unit
values. When a native unit is edited, BESTCOMSPlus automatically recalculates the per unit value based
on the native unit setting and the rated data parameter (on the System Parameters, Rated Data screen)
associated with it. When a per unit value is edited, BESTCOMSPlus automatically recalculates the native
value based on the per unit setting and the rated data parameter associated with it.
Once all per unit values are assigned, if the rated data parameters are changed, BESTCOMSPlus
automatically recalculates all native unit settings based on the modified rated data parameters.
The Undervoltage pickup has a native unit of Primary Volts and the rated data associated with it is
Machine Rated Data, Voltage (on the System Parameters, Rated Data screen).
BESTCOMSPlus
®
generator undervoltage settings are illustrated in Figure 10-4.
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