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TM 5-685/NAVFAC MO-912
and automatic equipment can be applied to the hy-
speed regulation of generators operated in parallel
should be the same for each machine. Speed regula-
draulic governor.
tion for generators operating individually should be
(a) The hydraulic governor requires pressur-
ized oil for operation. This oil can come from the
as favorable as possible without causing generator
surge resulting from sudden load changes. Ordi-
engine or from a separate sump in the governor. Oil
is admitted to an auxiliary oil pump in the governor.
narily, 2.5 percent speed regulation is satisfactory
The auxiliary pump furnishes necessary pressure to
Voltage regulation of DC generators may be accom-
actuate the governor mechanism. In the governor
plished through adjustment of the speed droop of
the governor.
shown, the fuel to the engine is decreased by the
g. Types of governors. Usually four types of gov-
action of the fuel-rod spring (10) on the fuel rod ( 12)
ernors are used; mechanical, hydraulic, pneumatic,
and increased by the opposing action of the hydrau-
and electronic. When speed regulation must be
lic serve piston (14), the admission of oil to which is
more precise, such as Defense Communications
controlled by a pilot valve (4). The pilot valve is
Agency sites where no more than 0.8 percent varia-
controlled by flyweights of the governor (5) which
tion is permitted, an electronic (isochronous) gover-
are driven by the governor shaft through gearing to
nor is used.
the engine. The centrifugal force of the flyweights in
(1) The mechanical governor used in small air-
rotation is opposed by the speeder spring (6), the
cooled engines may be part of the fly-wheel. The
compression of which determines the speed at
governor in multicylinder engines is usually a sepa-
which the governor will control the engine. The
rate assembly driven by gear or belt from a cam-
speeder-spring compression is adjusted through the
shaft or crankshaft. A typical mechanical governor,
rotation of the speed-adjusting shaft (8) which
shown in figure 3-12, operates as follows: the gov-
raises or depresses the spring fork (7) through its
ernor drive gear (2) drives the governor shaft (10)
linkage lever.
and the governor weights (4). Centrifugal force
(b) The droop of the speed-load characteristic
moves the weights away from the shaft which push
is adjusted by changing the effective length of the
the operating-fork riser (6) against the operating
floating lever (11). This is accomplished by moving
fork (ll), rotating the operating-fork shaft (7) and
the droop-adjusting bracket forward or backward in
moving the governor arm (9). In the external view,
the slot of the floating lever. The effective length of
the governor spring (A) is connected to the governor
the lever should be shortened to decrease the speed
arm and opposes movement of the governor weights
droop and lengthened to increase the speed droop.
away from the shaft. Adjusting screw (c) adjusts the
(3) The pneumatic governor (air-vane type) is
tension of the governor spring, establishing the
used in certain small generator plants (see fig
speed at which the prime mover operates. The
3-14). The engine flywheel includes an integral fan
greater the governor-spring tension, the lower the
which forces air outward from the drive shaft. The
governed speed. The auxiliary adjusting screw (D)
adjusts the droop of the governor. Turning this
amount of air flowing from the engine depends on
screw in closer to the arm decreases the droop of the
engine speed. A movable air vane is placed in the air
governor; this screw should be turned in as far as
stream. The air vane (blade) acts as a governor
possible without allowing the engine to surge. Aux-
since the air pressure depends upon engine speed.
iliary adjusting screw (B) is turned in to damp out
The air pressure on the vane is opposed by a gover-
surging of the engine at light-load or no-load; it
nor spring and these forces operate through linkage
should not be turned in so far that it increases the
to control the throttle of the engine.
speed of the generator at no-load.
(4) Electronic (isochronous) speed control is the
maintenance of constant engine speed independent
(2) The hydraulic governor (see fig 3-13) is
used on large prime movers as well as diesel en-
of the load being carried (zero droop). An isochron-
gines as small as 100 hp. The governor usually
ous governor will maintain, or can be adjusted to
maintain, constant engine speed (within 0.2 percent
includes: a speed-responsive device, usually fly-
variation). This type of governor can be a combina-
weights; a valve mechanism; a regulating cylinder
and piston; and a pressure pump and relief valve.
tion of a conventional hydraulic governor and an
electronic load-sensing system, or an all-electric
The assembly is adjustable for various ranges of
speed and sensitivity. The hydraulic principle pro-
vides greater power than could be obtained from a
(a) Speed control by the hydraulic governor,
mechanical type. Since the flyweights only control
see paragraph 3-8d(2), depends on variation in cen-
an easily moved pilot valve (which in turn controls
trifugal force created by flyweights (centrifugal
the hydraulic action), the governor can be made to
forces are not used in electric types). This force
operate accurately and smoothly. Remote control
operates a piston-type pilot valve which controls the

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