11-8 9440300990
Limiters DECS-250
Figure 11-9. Stator Current Limiting
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).
Low-Level Limiting
When the stator current exceeds the low-level setting, the DECS-250 annunciates the elevated level. If
this condition persists for the duration of the High SCL Time setting, the DECS-250 acts to limit the
current to the low-level SCL Setting. When the stator current is below the Low-Level SCL setting, no SCL
limiting action is taken by the DECS-250. The High Current Timer counts down either from the high time,
if the High Current Timer has expired, or from the amount of time spent at high level, if the High Current
Timer has not expired. The generator is permitted to operate indefinitely at or below the low-level
threshold.
High-Level Limiting
When the stator current exceeds the High-Level setting, the DECS-250 acts to limit the current to the
value of the High-Level setting and a High Level Timer is initiated. If this level of current persists until this
timer reaches the High-Level Time setting, the DECS-250 acts to limit the current to the value of the Low-
level SCL setting.
Initial Delay
In the case of low- or high-level stator current limiting, the limiting function will not respond until an initial
time delay expires.
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