maintenance personnel must have access to all
This manual covers the various types of auxiliary
other literature related to the equipment in use.
power generating systems used on military instal-
This includes military and commercial technical
lations. It provides data for the major components
manuals and engineering data pertaining to their
of these generating systems; such as, prime movers,
generators, and switchgear. It includes operation
b. Appendixes B through F provide details re-
of the auxiliary generating system components
lated to fuel storage, lubricating oil, coolant, forms
and the routine maintenance which should be
and records, and safety (including first aid). Texts
performed on these components. It also describes
and handbooks are valuable tools for the trained
the functional relationship of these components and
engineer, supervisor, and operator of a power plant.
the supporting equipment within the complete sys-
The manufacturers of the components publish de-
tailed operating, maintenance, and repair manuals.
Instructions, applicable to the equipment, are pro-
vided by each manufacturer and should be filed at
The guidance and data in this manual are intended
the plant for safekeeping and use. Replacement cop-
to be used by operating, maintenance, and repair
ies are available from each manufacturer.
personnel. It includes operating instructions, stan-
dard inspections, safety precautions, troubleshoot-
ing, and maintenance instructions. The information
Appendix A contains a list of references used in this
applies to reciprocating (diesel) and gas turbine
manual. Other pertinent literature may be substi-
prime movers, power generators, switchgear, and
tuted or used as supplements.
subsidiary electrical components. It also covers fuel,
air, lubricating, cooling, and starting systems.
1-4. Explanation of abbreviations and terms.
a. In addition to the information contained in
Abbreviations and special terms used in this
this manual, power plant engineers, operators, and
manual are explained in the glossary.
TM 5-685/NAVFAC MO-912
EMERGENCY POWER SYSTEMS
2-1. Emergency power.
ally is started manually; a class B plant may have
Emergency power is defined as an independent re-
either a manual or an automatic start system. Ac-
serve source of electric energy which, upon failure
cordingly, a class B plant is almost as costly to
or outage of the normal source, automatically pro-
construct and operate as a primary power plant of
vides reliable electric power within a specified time.
similar size. Usually, a class B plant is a
permanent-type unit capable of operating between
a. A reliable and adequate source of electric
1000 and 4000 hours annually. The class C plant
power is necessary for the operation of active mili-
always has an autostart control system (set to start
tary installations. Power must also be available at
the plant when the primary power voltage varies or
inactive installations to provide water for fire pro-
the frequency changes more than the specified op-
tection, energy for automatic fire alarms, light for
security purposes, heat for preservation of critical
(1) A class B plant (considered a standby long-
tactical communications and power equipment, and
term power source) is used where multiple commer-
for other operations.
cial power feeders are not available or extended and
b. Power, supplied by either the local utility com-frequent power outages may occur. Total fuel stor-
pany or generated on-site, is distributed over the
age must be enough for at least 15 days continuous
activity. The source of distribution may be subject to
brownout, interruption or extended outage. Mis-
(2) A class C plant is used where rapid restora-
sion, safety, and health requirements may require
tion of power is necessary to feed the load. More
an uninterruptible power supply (UPS) or
than one class C unit is usually used when the
standby/emergency supply for specific critical loads.
technical load exceeds 300 kW at 208Y/120 volts or
Justifiable applications for auxiliary generator are:
600 kilowatts (kW) at 48OY/277 volts. Spare class C
(1) Hospitals (life support, operating room,
units are sometimes provided for rotational mainte-
emergency lighting and communication, refrigera-
nance service. The autostart control system ensures
tion, boiler plant, etc.).
that the load is assumed as rapidly as possible.
(2) Airfields (control tower, communications,
Diesel engine prime movers may be equipped with
traffic control, engine start, security, etc.).
coolant and lubricating oil heaters to ensure quick
(3) Data processing plant systems.
starting. Recommended total fuel storage must be
(4) Critical machinery
enough for at least seven days continuous opera-
(5) Communication and security.
c. It is essential that a schematic showing the
c. Emergency generators must provide adequate
loads to be carried by an auxiliary generator be
power for critical loads of a building or a limited
available for reference. Do not add loads until it is
group of buildings, heating plants, utility pumping
approved by responsible authority.
plant, communication centers, or other such instal-
lations where interruption of normal service would
2-2. Types of power generation sources.
be serious enough to justify installation of an auxil-
a. The critical uses of electric power at a site
iary power plant. The plant must be reliable and
demand an emergency source of power whenever an
easily started in all seasons of the year. The plant
outage occurs. Selection of the type of auxiliary gen-
building should be completely fireproof with heating
erating plant is based on the mission of the particu-
and ventilation facilities that satisfy the plant’s re-
lar site and its anticipated power consumption rate
quirements. The space around the units should per-
during an emergency. The cost of plant operation
mit easy access for maintenance and repair. Space
(fuel, amortized purchase price, depreciation, and
should be provided within the building for safe stor-
insurance) and operation and maintenance person-
age of fuel such as a grounded and vented “day”
nel requirements must be analyzed. Future load
tank. Type and grade of fuel should be identified on
growth requirements of the site must be considered
the tank. Important considerations for these plants
for size selection.
included the following:
b. Auxiliary power generating plants are desig- (1) Selection of generators (size and quantity, nated as either class B or class C. The design crite- type of prime mover, and load requirements).
ria for a class B plant is comparable to those of a (2) Determination of need for instrumentation primary power plant. A primary power plant usu-
(meters, gauges, and indicator lights).
TM 5-685/NAVFAC MO-912
(3) Selection of protective equipment (relays
outlets and be well lighted with supplemental light-
and circuit breakers).
ing for instrument panels. Heat for the building
(4) Determination of need for automatic start-
should be steam, heat pumps or electric heaters to
ers, automatic load transfer, etc.
avoid hazards from explosive vapors.
(5) Selection of auxiliary generator size is
c. Prime movers require a constant supply of
based on satisfying the defined electrical load re-
large quantities of air for combustion of fuel. Com-
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).
trailers. Although the size of portable units may
d. Precautions must be taken when environmen-
vary from less than 1 kW to more than 1,000 kW,
tal conditions related to location of the generating
the most commonly used units are less than 500 kW
system are extreme (such as tropical heat and/or
capacity. Reciprocating prime movers are usually
desert dryness and dust). Cooling towers and spe-
used for portable power plants. Gas turbine engines
cial air filters are usually provided to combat these
are frequently employed for smaller units because
conditions. Arctic conditions require special heating
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
regulation through air-gap, pole-piece, and winding
(1) Foundations. A generator and its prime
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.
cially equipment having standby functions, should
(2) Floors. The floors are usually concrete with
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
ers and high-voltage switching equipment can be
gratings covering floor trenches must be grounded.
placed outdoors if they are designed with drip-proof
Rubber matting should be installed in front of and
around switchboards and electrical equipment to
b. The buildings housing large auxiliary power
minimize shock hazard.
generating systems (see fig 2-1) require adequate
ceiling height to permit installation and removal of
2-4. Fuel storage.
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
TM 5-685/NAVFAC MO-912
EXHAUST S I L E N C E R
V E N T
D U C T
C O O L I N G
V E N T I L A T I O N
L O U V E R S
C O N C R E T E
B A S E
V I B R A T I O N
D A M P E N E R S
Figure 2-l. Typical installation of an emergency power plant.
the operational requirements of the class B or class
age as liquids. Methods to determine tank contents
C generating plants that are used. Fuel logistics
are covered in paragraph 5-7 b(8).
should be considered when sizing fuel storage ca-
d. Day tanks. A grounded and vented day tank,
having not more than 275 gallons capacity, is in-
a. Fuels for the equipment described herein (re-
stalled within the power plant building. The tank is
fer to app C) are combustible substances that can be
normally filled by transfer pump from the installa-
burned in an atmosphere of oxygen. Two categories
tion’s main storage tank. Provision should be made
of fuel storage are discussed: liquids and gases. In
to fill the day tank by alternate means (or directly
either case, fuel storage tanks, associated pumps
from safety cans or barrels) if the transfer system
and piping systems must be grounded and protected
from galvanic, stray current or environmental cor-
b. Liquid fuel for auxiliary power generating sys-Most electrical plants serve a varied load of light-
tems is usually stored in buried tanks equipped
ing, heating equipment, and power equipment,
with vent pipes and manholes. Above-ground tanks
some of which demand power day and night. The
may be used for storage at some locations. These
annual load factor of a well-operated installation
tanks usually have provisions for venting, filling
will be 50 percent or more with a power factor of 80
and cleaning. A gauge with indicator is used to de-
percent or higher. Equipment and controls must be
termine tank contents. Two tanks are necessary to
selected to maintain frequency and voltage over the
ensure a continuous supply during tank cleaning
(every two years) and maintenance operations. Pro-
visions must be made to use a gauge stick to posi-
2-6. Distribution systems.
tively determine depth of tank contents. Storage
a. The load determines direct current (DC) or tanks should be checked for settled water accumu-alternating current (AC), voltage, frequency (DC, 25
lated through condensation and the free water
Hertz (Hz), 50 Hz, 60 Hz, 400 Hz), phases and AC
configuration (delta or wye). Voltage and other pa-
c. Gaseous fuel is stored in tanks either as a gas
rameters of the distribution system will have been
or a liquid, depending on the type of fuel. Natural
selected to transmit power with a minimum of con-
gas is stored as a gas. Butane and propane are
version (AC to DC), inversion (DC to AC), (AC)
cooled and kept under moderate pressure for stor-
transformer, impedance, and resistance loss. For a
TM 5-685/NAVFAC MO-912
given load; higher voltage, unity power factor, low
longer insulation life of generators, motors, trans-
resistance/impedance, and lower frequency gener-
formers, and other system components by suppress-
ally result in lower distribution losses. Use of equip-
ing transient and sustained overvoltages associated
ment to change or regulate voltage, frequency or
with certain fault conditions. In addition, system
phase introduces resistance, hysteresis and me-
grounding improves protective relaying by provid-
ing fast, selective isolation of ground faults.
b. A lagging power factor due to inductive loads
b. Equipment grounding, in contrast to system
(especially under-loaded induction motors) results
grounding, relates to the manner in which
in resistive losses
because greater current is
noncurrent-carrying metal parts of the wiring sys-
required for a given power level. This may be cor-
tem or apparatus, which either enclose energized
rected by the use of capacitors at the station bus or
conductors or are adjacent thereto, are to be inter-
by “run” capacitors at induction motors to have the
connected and grounded. The objectives of equip-
generator “see” a near-unity but yet lagging power
ment grounding are:
(1) To ensure freedom from dangerous electric
c. Overcorrection, resulting in a leading (capaci-
shock-voltage exposure to persons.
tive) power factor must be avoided. This condition
(2) To provide current-carrying capability dur-
results in severe switching problems and arcing at
ing faults without creating a fire or explosive haz-
contacts. Switching transients (voltage spikes, har-
monic transients) will be very damaging to insula-
(3) To contribute to superior performance of the
tion, controls and equipment. The electronics in ra-
dio, word and data processing, and computer arrays
c. Many personal injuries are caused by electric
are especially sensitive to switching and lighting
shock as a result of making contact with metallic
transients, over/under voltage and frequency
members that are normally not energized and nor-
mally can be expected to remain non-energized. To
d. The distribution system must include sensing
minimize the voltage potential between noncurrent-
devices, breakers, and isolation and transfer feed
carrying parts of the installation and earth to a safe
switches to protect equipment and personnel.
value under all systems operations (normal and ab-
normal), an installation grounding plan is required.
d. System grounding. There are many methods of The frequency required by almost all electrical
system grounding used in industrial and commer-
loads is the standard 50 or 60 Hz. Most electrical
cial power systems (refer to fig 2-2), the major ones
equipment can operate satisfactorily when the fre-
quency varies plus or minus ten percent
Steady state frequency tolerance (required for
(2) Solidly grounded.
frequency-sensitive electronic equipment) should
(3) Resistance grounding: low-resistance, high-
not exceed plus or minus 0.5 percent of design fre-
quency. Since some equipment are sensitive to fre-
(4) Reactance grounding.
quency changes, operators must closely monitor fre-
e. Technically, there is no generally accepted use
quency meters and regulate frequency when
of any one particular method. Each type of system
grounding has advantages and disadvantages. Fac-
tors which influence the choice of selection include:
(1) Voltage level of the power system.
Grounding implies an intentional electrical connec-
(2) Transient overvoltage possibilities.
tion to a reference conducting plane, which may be
(3) Type of equipment on the system.
earth (hence the term ground) but more generally
(4) Cost of equipment.
consists of a specific array of interconnected electri-
(5) Required continuity of service.
cal conductors referred to as grounding conductors.
(6) Quality of system operating personnel.
The term “grounding” as used in electric power sys-
(7) Safety considerations, including fire hazard
tems indicates both system grounding and equip-
ment grounding, which are different in their objec-
f. An ungrounded system is a system in which
there is no intentional connection between the neu-
a. System grounding relates to a connection from
tral or any phase and ground. “Ungrounded system”
the electric power system conductors to ground for
literally implies that the system is capacitively
the purpose of securing superior performance quali-
coupled to ground.
ties in the electric system. There are several meth-
(1) The neutral potential
of an ungrounded sys-
ods of system grounding. System grounding ensures
tern under reasonably balanced load conditions will
TM 5-685/NAVFAC MO-912