7-6 9440300990
Regulation DECS-250
cross-current compensation (reactive differential) schemes for reactive load sharing. A separate load
sharing function enables each machine to share the load proportionally without incurring a voltage and
frequency droop.
Paralleled generator settings are illustrated in Figure 7-5 and described in the following paragraphs.
Reactive Droop Compensation
Droop compensation serves as a method of controlling reactive current when the generator is connected
in parallel with another energy source. Droop compensation utilizes the B-phase CT in single-phase
applications. When droop compensation is enabled, the generator voltage is adjusted in proportion to the
measured generator reactive power. The reactive droop compensation setting is expressed as a
percentage of the generator rated terminal voltage.
For droop compensation to operate, the PARALLEL_EN_LM logic
block must be set true in BESTlogic™Plus programmable logic.
Cross-Current Compensation
Cross-current compensation (reactive differential) mode serves as a method of connecting multiple
generators in parallel to share reactive load. When reactive load is shared properly, no current is fed into
the DECS-250 cross-current compensation input (which is connected to the B-phase transformer).
Improper sharing of reactive load causes a differential current to be fed into the cross-current
compensation input. When cross-current compensation is enabled, this input causes the DECS-250 to
respond with the proper level of regulation. The response of the DECS-250 is controlled by the cross-
current compensation gain setting which is expressed as a percentage of the system nominal CT setting.
Application information about cross-current compensation is available in the Voltage and Current chapter
of this manual.
Network Load Sharing
In a multiple-generator application, the load sharing function ensures equal generator reactive-power
sharing. It operates in a similar manner to cross-current compensation but without the external hardware
requirements and distance limitations. Instead of sharing load based on the CT ratio, load is shared on a
per-unit basis calculated from the generator rated data. Sharing of load information between DECS-250
controllers is accomplished through the Ethernet port of each DECS-250 communicating over a peer-to-
peer network dedicated for the load sharing function. Each DECS-250 measures the reactive current of
its associated generator and broadcasts its measurement to all other DECS-250 controllers on the
network. Each DECS-250 compares its level of reactive current to the sum of all measured currents and
adjusts its excitation level accordingly.
A Load Share ID setting identifies the DECS-250 as a load sharing unit in the network. Checking a Load
Sharing Unit number box allows any DECS-250 load sharing units on the network with that Load Share ID
number to share load with the currently connected DECS-250. It is not necessary for the Load Share ID
to be unique for each unit. This allows for load sharing units to be grouped.
When the unit’s configuration does not match the configuration of the other units with load sharing
enabled, the Network Load Share Config Mismatch logic element becomes true. The Configuration
Mismatch Delay setting adds a delay before the element becomes true.
Load sharing settings consist of an Enable checkbox and Droop, Kg, Ki, Max Vc, Configuration Mismatch
Delay, and Load Share ID settings.
Line Drop Compensation
When enabled, line drop compensation can be used to maintain voltage at a load located at a distance
from the generator. The DECS-250 achieves this by measuring the line current and calculating the
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