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TM 5-685/NAVFAC MO-912
outlets and be well lighted with supplemental light-
(3) Selection of protective equipment (relays
ing for instrument panels. Heat for the building
and circuit breakers).
should be steam, heat pumps or electric heaters to
(4) Determination of need for automatic start-
avoid hazards from explosive vapors.
ers, automatic load transfer, etc.
c. Prime movers require a constant supply of
(5) Selection of auxiliary generator size is
large quantities of air for combustion of fuel. Com-
based on satisfying the defined electrical load re-
quirement (expressed as kilowatts).
bustion produces exhaust gases that must be re-
d. Portable power plants are widely used on mili-
moved from the building since the gases are hazard-
tary installations because of the temporary nature
ous and noxious. The air is usually supplied via a
of many applications. The power plants (including a
louvered ventilation opening. Exhaust gases are
diesel or gas turbine prime mover) are self-
conducted to the outside by piping that usually in-
contained and mounted on skids, wheels, or semi-
cludes a silencer or muffler (see fig 2-l).
d. Precautions must be taken when environmen-
trailers. Although the size of portable units may
tal conditions related to location of the generating
vary from less than 1 kW to more than 1,000 kW,
system are extreme (such as tropical heat and/or
the most commonly used units are less than 500 kW
desert dryness and dust). Cooling towers and spe-
capacity. Reciprocating prime movers are usually
used for portable power plants. Gas turbine engines
cial air filters are usually provided to combat these
conditions. Arctic conditions require special heating
are frequently employed for smaller units because
of their relatively light weight per horsepower.
e. Portable diesel powered generators usually op-
e. When required for the auxiliary generating
erate at 1200, 1800 or 3600 revolutions per minute
equipment, the building or enclosure should be fire-
(rpm), since high speeds allow a reduction in weight
proof and constructed of poured concrete or concrete
of the generator plant. To keep weight down, such
and cinder blocks with a roof of reinforced concrete,
ancillary equipment as voltage regulators, electric
steel, or wood supports with slate or other fireproof
starters and batteries are sometimes omitted from
shingles. Ventilation and openings for installation
the smaller generators. Starting may be done by
of materials and equipment should be
crank or rope, ignition by magneto, and voltage
(1) Foundations. A generator and its prime
regulation through air-gap, pole-piece, and winding
design. Portable plants usually have a minimum
mover should be set on a single, uniform foundation
number of meters and gauges. Larger size portable
to reduce alignment problems. The foundation
units have an ammeter, a frequency meter, a volt-
should be in accordance with manufacturer's recom-
meter, and engine temperature and oil pressure
mendations for proper support of equipment and
gauges. Generator protection is obtained by fused
dampening of vibrations. Foundation, prime mover,
switches or air circuit breakers.
and generator should be mechanically isolated from
the building floor and structure to eliminate trans-
2-3. Buildings and enclosures.
mission of vibrations. All mechanical and electrical
a. Auxiliary power generating equipment, espe-
connections should allow for vibration isolation.
(2) Floors. The floors are usually concrete with
cially equipment having standby functions, should
be provided with suitable housings. A typical power
non-skid steel plates over cable and fuel-line
plant installation is shown in figure 2-l. The equip-
trenches. The floor space should provide for servic-
ment should be located as closely as possible to the
ing, maintenance, work benches, repair parts, tool
load to be served. Generators, prime movers,
cabinets, desks, switchboard, and electrical equip-
switchboards, and associated switching equipment
ment. Battery bank areas require protection from
should always be protected from the environment.
corrosive electrolytes. Floors must be sealed to pre-
Many small units are designed for exterior use and
vent dusting, absorption of oils and solvents, and to
have their own weatherproof covering. Transform-
promote cleanliness and ease of cleanup. Plates and
gratings covering floor trenches must be grounded.
ers and high-voltage switching equipment can be
Rubber matting should be installed in front of and
placed outdoors if they are designed with drip-proof
around switchboards and electrical equipment to
b. The buildings housing large auxiliary power
minimize shock hazard.
generating systems (see fig 2-1) require adequate
2-4. Fuel storage.
ceiling height to permit installation and removal of
cylinder heads, cylinder liners, pistons, etc., using
Fuel storage space should be provided near the
chain falls. An overhead I-beam rail, or movable
plant, with enough capacity to allow replenishment
structure that will support a chain fall hoist, is
in economical, reasonable intervals. The total fuel
necessary. The building should have convenience
storage capacity should be large enough to satisfy

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