Basler Electric DGC-2020 - Manual (Page 334)

15. Next, click on the I/O tab and drag the selected output contacts into the main logic. Connect the
Governor and AVR blocks to the appropriate outputs. This concludes implementation of the automatic
synchronizer. See Figure 7-53.
Figure 7-53. Settings Explorer, BESTlogicPlus Programmable Logic (Step 15)
Setting up a DGC-2020 and LSM-2020 for a Load Sharing and kW
Control Application
The following paragraphs provide information and setup procedures for load sharing and kvar control
using the DGC-2020 and LSM-2020.
Load Sharing Overview and Theory of Operation in the DGC-2020
Load sharing is necessary when multiple generators are tied to a common bus driving a load and not
connected to the utility; the generators are the only power source. Such a system is referred to as an
“Islanded System”. Load sharing is accomplished by putting all of the governors in speed droop mode;
however, when speed droop is employed, the system speed and frequency may not be maintained. As
load increases, system speed drops. The throttles can be adjusted to resume desired speed, but if the
load varies, it can be difficult to maintain the speed of the system. In systems where speed and frequency
deviation is problematic, speed droop control is not the most appropriate load sharing method.
Isochronous (constant speed) load sharing can be accomplished using a system load share line. The load
sharing electronics provide a bias to the governors’ analog bias inputs to implement sharing of kW among
the machines. In such systems, all machines share load equally on a percentage of capacity basis.
Furthermore, many load sharing devices include a speed trim feature, which actively controls the speed of
each generator in the island system to maintain desired system frequency.
The heart of the load sharing system is the load share line. The voltage on the load share line will range
between some minimum values, indicating the system is not loaded, to some maximum value, indicating
the system is fully loaded. By measuring the load share line voltage, the user can determine the amount
of system load. If the voltage is halfway between the minimum and maximum load share voltages, it is
indicated that the average system load is 50 percent capacity.
Each load share device must drive the load share line with a voltage that is proportional to its percentage
of load. The load share line outputs from all devices are connected together. Therefore, each load share
device must contain an internal resistor between the voltage driver and the load share line output to limit
the current from the voltage driver. The voltage on the connection point is the average of the load share
7-46 DGC-2020 Setup 9400200990 Rev X