9440300990 7-5
DECS-250 Regulation
Figure 7-3. Pre-Position Setpoints
Transient Boost
The transient excitation boosting function improves response to successive faults by providing increased
excitation support. When a simultaneous line current increase and line voltage decrease occurs, the
DECS-250 compensates by elevating the voltage setpoint above the nominal setpoint. When the line
voltage recovers, the voltage setpoint is restored to the nominal value.
Fault detection is controlled by a voltage threshold setting, a current threshold setting, and a duration
setting. Fault voltage threshold is expressed as a percentage of the AVR setpoint and fault current
threshold is expressed as a percentage of the rated field current. The duration setting determines how
long a fault condition is tolerated before the setpoint is adjusted.
Setpoint adjustment is controlled by a voltage setpoint boosting level, a clearing voltage threshold, and a
clearing voltage delay. The setpoint boosting level is expressed as a percentage above the AVR setpoint.
Transient boost is disabled once the line voltage recovers above the clearing voltage threshold. The
clearing voltage threshold is expressed as a percentage below the AVR setpoint. The clearing voltage
delay determines how long the line voltage must exceed the clearing voltage threshold before setpoint
adjustment is terminated.
Figure 7-4. Transient Boost Settings
Operation with Paralleled Generators
BESTCOMSPlus Navigation Path: Settings Explorer, Operating Settings, Parallel/LineDrop
Compensation
HMI Navigation Path: Settings, Operating Settings, Parallel/LineDrop Compensation
The DECS-250 can be used to control the excitation level of two or more generators operating in parallel
so that the generators share the reactive load. The DECS-250 can employ either droop compensation or
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