9400200990 Rev I DGC-2020 Functional Description 3-9
or none. BESTCOMSPlus is used to configure breaker management. Refer to Section 4,
BESTCOMSPlus Software, Breaker Management, for setting information.
Determining Breaker Status
The status of the breakers is determined by using BESTlogic+ Programmable Logic to setup the
GENBRK and MAINSBRK logic blocks. These logic blocks have outputs that can be configured to
energize an output contact and control a breaker as well as inputs for breaker control and status.
Processing Breaker Requests
Types of breaker operate requests include:
• Local Request - generated by internal functions and based on operating modes.
• Com Request - generated through a communication port using BESTCOMSPlus or the front panel
HMI.
• Logic Request - generated from the PLC (programmable logic controller).
The type of response given for a local request depends on the operating mode of the DGC-2020.
RUN Mode
When in RUN mode, the generator and mains breakers can be closed manually using contact inputs or
the breaker buttons on the BESTCOMSPlus Control screen.
OFF or AUTO Mode (Not Running)
If operating in the OFF mode or AUTO and not running, the generator breaker cannot be closed because
the generator will not be stable.
AUTO Mode (Running)
When in AUTO mode and running, the mains fail transfer feature will automatically control the mains
breaker and the generator breaker or the external ATS (automatic transfer switch) will start the generator
and control the breakers itself. In addition, the generator breaker can be automatically controlled by the
demand start/stop function, the exercise timer function, or a RUNWLOAD (run with load) start from the
PLC. The generator breaker can be manually controlled using contact inputs and outputs or the breaker
buttons on the BESTCOMSPlus Control screen.
Breaker Operation
The DGC-2020 will attempt to close a breaker only after verifying that it can be closed. If the breaker
cannot be closed, the close request will be ignored. Only one breaker can be closed at a time.
Synchronization is required before closing the breaker to a live bus. Closure to a dead bus can be
performed after meeting dead bus threshold and timing requirements set by the user.
Determining if it is Acceptable to Close a Breaker
Before the generator breaker can be closed, it must be configured in BESTCOMSPlus. If only the
generator breaker is configured (mains breaker not configured) the DGC-2020 looks at user settings to
determine if the generator side of the breaker is stable and the bus side is stable or dead. If both the
generator and the mains breakers are configured and open, the DGC-2020 will close the generator
breaker if the generator side of the breaker is stable. If both breakers are configured and the mains
breaker is closed, the DGC-2020 will close the generator breaker after verifying that both sides of the
generator breaker are stable and the DGC-2020 is synchronizing.
Before the mains breaker can be closed, it must be configured in BESTCOMSPlus. If both the mains and
the generator breakers are configured and open, the DGC-2020 will close the mains breaker if the mains
side of the breaker is stable. If both breakers are configured and the generator breaker is closed, the
DGC-2020 will close the mains breaker after verifying that both sides of the mains breaker are stable.
Changing the Breaker State
Synchronization is required when closing a breaker to a live bus. Bus conditions act as a supervisory
control over the synchronizing function. If synchronization is in process and either bus goes unstable,
synchronization is suspended. To close the breaker on a dead bus, the DGC-2020 generates a breaker
close request. The closing function is then run without synchronization.
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