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Synchronizer DECS-250
Use caution when connecting a “dead” generator to a “dead” bus.
Undesired system damage can occur if the bus becomes energized
while a “dead” generator is connected to it.
Figure 6-3. Breaker Hardware Configuration Settings
Generator and Bus Condition Detection
BESTCOMSPlus Navigation Path: Settings Explorer, Synchronizer/Voltage Matching, Bus Condition
Detection
HMI Navigation Path: Settings, Sync/Voltage Matching, Bus Condition Detection
The DECS-250 monitors the voltage and frequency of the generator and bus for determining when a
breaker closure is appropriate. Generator and bus condition detection settings are illustrated in Figure
6-4.
Generator Condition
A dead generator is recognized by the DECS-250 when the generator voltage decreases below the dead
generator threshold for the duration of the dead generator activation delay.
A failed generator is recognized when the generator voltage or frequency does not meet the established
generator stability criteria for the duration of the failed generator activation delay. Generator stability
parameters are described in Generator Stability.
Generator Stability
Before initiating a breaker closure (tying the generator to a stable or dead bus), the generator voltage
must be stable. Several settings are used to determine generator stability. These settings include pickup
and dropout levels for overvoltage, undervoltage, overfrequency, and under-frequency. Recognition of
generator stability is further controlled by a generator stability activation delay. Breaker closure is not
considered if the voltage conditions are not within the stability pickup and dropout settings for the duration
of the stability activation delay.
Bus Condition
A dead bus is recognized by the DECS-250 when the bus voltage decreases below the dead bus
threshold for the duration of the dead bus activation delay.
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