9492600990 9-3
DECS-150 Limiters
The online, low-level OEL threshold is determined by the Low Level setting. When the excitation level is
below the Low Level setting, no action is taken by the DECS-150. The generator is permitted to operate
indefinitely with this level of excitation. When the excitation level exceeds the Low Level setting for the
duration of the high and medium time settings, the DECS-150 acts to limit the excitation to the value of
the Low Level setting. The Ambient Temperature setting on the Rated Data Settings screen determines
the low-level range.
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 levels have native units of Primary Amps and the rated data associated with them is Machine Rated
Data, Current (on the System Parameters, Rated Data screen).
Summing point OEL settings are illustrated in Figure 9-4.
Figure 9-4. Summing Point OEL Screen
Takeover OEL
Takeover OEL limits the field current level in relation to an inverse time characteristic similar to that
shown in Figure 9-5. Separate curves may be selected for online and offline operation. If the system
enters an overexcitation condition, the field current is limited and forced to follow the selected curve. The
inverse time characteristic is defined by Equation 9-1.
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