EGCP-2 Engine Generator Control Package Manual 26086
72 Woodward
Isochronous
Isochronous means repeating at a single rate or having a fixed frequency or
period. A generating set operating in the isochronous mode will operate at the
same set frequency regardless of the load it is supplying up to the full load
capability of the generator set, as illustrated in Figure 4-2. This mode can be
used on one generator set running by itself in an isolated system.
Figure 4-2. Isochronous Mode
The isochronous mode can also be used on a generator set connected in parallel
with other generator sets. Unless the generator set controls have the capacity for
load sharing and speed control, no more than one of the generator sets
operating in parallel can be in the isochronous mode. If two generator sets
operating in the isochronous mode without load sharing capability are tied
together to the same load, one of the units will try to carry the entire load and the
other will shed all of its load. In order to share load with other units, some
additional means must be used to keep each generator set from either trying to
take all the load or from motorizing.
Droop/Isochronous Load Sharing on an Isolated Bus
Droop/Isochronous combines the first two modes. All generator sets in the
system except one are operated in the droop mode. The one unit not in droop is
operated in the isochronous mode. It is known as the swing machine. In this
mode, the droop machines will run at the frequency of the isochronous unit. The
droop and speed settings of each droop unit are adjusted so that each generates
a fixed amount of power as illustrated in Figure 4-3. The output power of the
swing machine will change to follow changes in the load demand.
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