10-4 9440300990
Protection DECS-250
Figure 10-4. Generator Undervoltage Protection Settings
Generator Overvoltage
An overvoltage pickup condition occurs when the sensed generator terminal voltage increases above the
pickup setting. An overvoltage trip condition occurs if the generator voltage remains above the pickup
threshold for the duration of the time delay setting. Generator overvoltage protection can be enabled and
disabled without altering the pickup and time delay settings. Overvoltage 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 Overvoltage 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 overvoltage settings are illustrated in Figure 10-5.
Figure 10-5. Generator Overvoltage Protection Settings
Loss of Sensing
The generator voltage is monitored for a loss of sensing (LOS) condition. LOS protection settings are
illustrated in Figure 10-6.
In the DECS-250, a loss of sensing (LOS) event is calculated using sequence components. LOS trip
criteria is listed in Table 10-1.
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