base) will be shown on the project plans, including
the power source for associated fans and pumps.
Governor. The type of governor to be used on each
engine generator set should be identified as
isochronous or droop on the engine-generator set
parameter schedule. Isochronous governors hold
frequency at the setpoint frequency (within
bandwidth) for all steady state loads from 0 to 100%
load and are required for applications where severe
demands are made on voltage and frequency
regulation. Droop governors allow frequency to
droop to the specified percentage proportional to
steady state loads from 0 to 100% load and are
generally acceptable for general purpose and
commercial applications.
Engine-generator sets in stand alone service
(isolated bus) may utilize either droop or
isochronous governors. The designer should analyze
the application and loads to determine if the more
expensive isochronous unit is actually required.
Droop units provide added stability (less engine
cycling) in single unit applications where constant
speeds are not critical and are less expensive than
isochronous governors.
Engine-generator sets in parallel (on an isolated
bus) may also utilize either droop or isochronous
governors. Load swings are shared proportionally
based on the governor droop settings. The load will
be split equally among the units for all units
equipped with isochronous governors with load
sharing controls, or if all units have droop
governors that are set with the same droop. "Lead
units" are often designated in multiple unit
applications for tighter frequency control by
setting one governor at a much lower droop than the
others. A "lead unit" can be designated for gensets
equipped with isochronous governors if all units
have governors with load sharing controls. In this
case the "lead unit" will accept all load swings and
the other units will remain at a constant load.
When all units have droop governors, the "lead
units" will accept most of the load swings and the
other units will equally split a small portion of
the load. If isochronous governors are specified
for two or more units to be paralleled on an
isolated bus, the governors must be specified with
load sharing controls. For applications involving
units in parallel operation which are not operator
supervised the designer should specify a
load-sharing system which can proportionally load
two or more sets in parallel, each having
isochronous governors. Generators for use with
existing generators in parallel applications must
have similar characteristics. Droop paralleling is
specified for electrical and electro-hydraulic
governors where interconnection of all controls is
SECTION 16263A
Page 19
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