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|  MIL-G-24477(SHIPS)
3.3.1 Reduced weight and size shall be considered as major factors in the generator
design. The generator shall be of single, sleeve type bearing and shall have the engine
end of the shaft piloted in the engine crankshaft. The generator half of the coupling
flanges shall be an integral part of the generator shaft forging. A sight flow fitting
shall be provided at the bearing oil discharge.
3.3.2 The lower half (up to the bottom of the shaft) of the generator enclosure shall
be watertight, and the upper half of the enclosure shall be spraytight.
3.3.3 The generator air cooler shall be in accordance with class 1 of MIL-C-19836
and shall be designed for the "submergence design pressure" and "submergence test pressure"
specified (see 6.1). Cooling water shall be furnished from the engine seawater system.
3.3.4 The generator efficiency shall be not less than 88 percent at 50 percent load
and 91.5 percent at 100 percent load.
3.3.5 Heaters shall be for 440 volt, three phase 60 Hertz operation, and shall be of
the rating required.
3.3.6 The generator (and associated excitation and voltage regulation system) shall be
capable of withstanding without injury to any part, a three phase or single phase short
circuit at the terminals for a period of 30 seconds with the generator under automatic
control of the voltage regulator. The sustained value of current during a three-phase short
circuit shall be at least 3.2 times rated current. Total temperatures during these periods
shall not exceed safe valves.
3.3.7 At rated frequency and at a p.f. of 0.5 or less lagging, the generator, when
under control of its voltage regulator, shall be capable of delivering 150 percent rated
current for 1 minute and maintaining the terminal voltage within 5 percent of rated voltage.
3.3.8 Where tapered keys or wedges are used in conjunction with dovetail laminations
to secure the complete pole assembly to the rotor spider, means shall be provided to prevent
their loosening due to shock or excessive vibration.
3.3.9 Requirements covering bearing thermostatic switch and temperature indicating
equipment of MIL-G-3124 and air temperature alarm of MIL-C-19836 do not apply.
In lieu
thereof, continuous reading resistance type thermometers shall be provided for measuring
the temperature of the air in and out of the cooler and the bearing, and shall be mounted
on the engine gage board.
3.3.10 The location and arrangement of the generator main terminals, cooler connections,
field rectifier terminals (If rectifiers are mounted in air stream and terminals are located
outside generator enclosure) , and heater connections shall be as required by the installation.
A mounting pad or flange shall be provided for the attachment of a shipbuilder furnished
terminal box for the main terminals and rectifier terminals if required.
3.3.11 Damper windings shall be provided and shall be connected between poles.
3.3.12 Wave shape.
3.3.12.1 Deviation factor. The deviation factor of the open circuit terminal voltage
shall not exceed 6 percent on any or all phases.
3.3.12.2 Harmonic content. From no load to full load, the r.m.s. value of the sum of
all harmonic components in the output voltage wave shall not exceed 5 percent of the r.m.s.
value of the rated output voltage. No single harmonic shall exceed 3 percent. Harmonics of
0.2 percent or less may be disregarded in the determination of the total harmonic content.
3.4 Excitation and voltage regulation system. The excitation and voltage regulation
system shall be of the completely static type in accordance with type III of MIL-R-2729
except as otherwise specified herein.
3.4.1 Voltage regulator.
The voltage regulator shall have the following classification:
(a)
Type of control . . . . . . .
.
Static
Protected for switchboard mounting
(b)
Enclosure . . . . . . . . . .
.
(c)
Regulators per switchboard .
.
One normal
(d)
Operation . . . . . . . . . .
.
Parallel (see 3.1.6)
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