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 (a) A typical speed regulation for a governor operating with droop is 3 percent. Thus,
if speed and frequency at full load are 1800 rpm and 60 Hz, at no load they would be
approximately 1854 rpm and 61.8 Hz.
A governor would be set for droop only when operating in parallel (in this mode f = 60 Hz +/- 0)
with a larger system or in parallel with another generator operating in the isochronous mode. In
this way, system frequency is maintained and the droop adjustment controls load distribution
among parallel engine generators.
(b) Under steady (or stable) load, frequency tends to vary slightly above and below the
normal frequency setting of the governor. The extent of this variation is a measure of the
stability of the governor. An isochronous governor should maintain frequency regulation within
+/- 1/4 percent under steady load.
(c) When load is added or removed, speed and frequency dip or rise momentarily,
usually for 1 to 3 seconds, before the governor causes the engine to settle at a steady speed at the
new load.
1.6.5.2 Starting Methods. Most engine generator sets use a battery-powered electric motor
for starting the engine. A pneumatic or hydraulic system normally is used only where starting of
the electric plant is initiated manually.
1.6.6 Turbine-Driven Generators. Steam and petroleum are two general types of turbine
prime movers for electrical generators currently available.
1.6.6.1 Steam Turbine Generators. Steam turbines are used to drive generators larger than
those driven by diesel engines. Steam turbines are designed for continuous operation and usually
require a boiler with a fuel supply and a source of condensing water. Because steam boilers
usually have electrically powered auxiliary fans and pumps, steam turbine generators cannot start
during a power outage. Steam turbine generators are, therefore, too large, expensive, and
unreliable for use as an emergency or standby power supply. They may also experience
environmental problems involving: fuel supply, noise, combustion product output, and heating of
the condensing water. Steam turbines may also be used in cogeneration systems, where steam
may be extracted from the turbine to serve process loads. In this configuration, no steam is
condensed at the turbine exhaust, but rather the turbine operates with a back pressure and serves
as a pressure reducing station.
1.6.6.2 Turbine Generators (Petroleum). The most common turbine-driven electric
generator units employed for emergency or standby power today use gas or oil for fuel. Various
grades of oil and both natural and propane gas may be used. Other less common sources of fuel
are kerosene or gasoline. Gas or oil turbine generators can start and assume load within 40
seconds to several minutes for larger units. Gas turbine generators are generally used as
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