Quantcast Motor-Generator Sets

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MIL-HDBK-1038
Where
G
=
generator rating in kW
T
=
minimum calculated running travel drive horsepower
H
=
minimum calculated running main hoist horsepower
M
=
minimum calculated horsepower for the third largest drive
A
=
ancillary loads (transformer rating in kVA)
Anti-condensation heaters are required to be installed in generators.  They are
required to be de-energized whenever the generators rotate.  All heaters
are required to be fed from a separate panel dedicated to equipment heater and
battery charger circuits.
The diesel engine driving the auxiliary diesel engine-generator set is a
much smaller machine than is the main diesel engine.  The horsepower rating of the
diesel engine, and the power rating of the auxiliary generator, should be based
upon, in addition to lighting and other ancillary loads, the power requirements of
the charger for the diesel engine's own batteries and of the motor for the air
compressor associated with the starting system for the main diesel engine, if
used.  The diesel engine's speed is 1800 rpm for continuous duty applications or
3600 rpm for intermittent duty applications.
5.5.5.2
Motor-Generator Sets.  Power conversion to DC from AC for
electro-mechanical adjustable voltage DC systems is accomplished through the use
of motor-generator sets.  The generators are required to be rated for continuous
duty operation.  The motor is required to be sized for simultaneous operation of
specific drives.  The motor-generator set is required to be provided with a
reduced-voltage type squirrel cage motor starter with thermal overload protection,
a generator field quenching circuit, and edgewound generator field resistors.
Generator output voltage is required to be varied by the use of magnetic field
relays to shunt out segments of the field resistors or by the use of a manually
operated rheostat.  (Drive motor direction is required to be changed by reversal
of generator field polarity.)  Particular attention is required to be given to the
positioning of the generators so that the brushes are easily accessible for
maintenance and inspection.
5.5.5.3
Motors.  The selection of the type of motor to be used in a given drive
train is dependent upon the type of power that is available to energize the motor,
the desired performance characteristics for the drive, and the type of control
equipment that is preferred.  Motors are designed either to operate on alternating
current power or to operate on direct current power.  Therefore, the selection of
the type of motor to be used is limited to those which would operate on the power
available.  Generally, AC power is available on bridge cranes and AC or DC power
is available on portal, floating, or container cranes.  Motor speed is either
affected by the load or it isn't.  So, if constant speed, regardless of load, is
desired, a squirrel cage AC motor or a shunt-wound DC motor is to be the choice.
If faster speed with lighter loads under the hook is desirable, then a wound-rotor
AC motor or a series-wound DC motor is to be selected.  The total gear ratio
between a motor and its driven load is required to be computed, not on the motor's
base or synchronous speed, but on the actual speed produced by the motor when
developing the required torque to maintain the desired rated load running speed.
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