MIL-DTL-3124E(SH)
3.3.23 Special noise limitations. When special airborne and structureborne noise limitations are required for
the application, details of limitations for airborne and structureborne noise (whether generator and detached units
should be resiliently mounted, the type of resilient mount to be used, and the procedure for noise tests) shall be
specified (see 6.2). The following factors shall be considered in the construction of the generator, as necessary, to
meet the noise limitations:
a.
Precision machining of rolling, rubbing, and fitted parts.
b.
In the production phase, minimize corrections required during the final balancing phase of the generator.
c.
In-place balancing of the rotor and provision for access plates for the in-place balancing.
d. Avoid sharp cutoffs and turbulence in air cooling systems. Ventilation ducts and housing shall be damped
to prevent flow excited vibration.
e.
Favorable combination of the following generator design features:
(1) Number of slots for each pole pitch.
(2) Number of slots magnetically under one pole.
(3) Slot frequency as a function of the natural frequency of the magnetic frame.
(4) Skewing of stator slots.
(5) Skewing of pole tips and fairing of pole tip edges.
f.
Spring mounting of generator stator punchings.
g.
Close tolerance of generator air gap.
h.
Any other features specified (see 6.2).
3.3.24 Salient-pole generators. For salient-pole generators, the requirements of 3.3.24.1 through 3.3.24.5 shall
apply.
3.3.24.1 Armature windings. Armature windings for generators with frame sizes corresponding to 25 kilowatts
at 1800 r/min and larger shall be form-wound (wound, formed, and insulated with or without impregnation before
assembly in core slots) and interchangeable with duplicate windings. The windings shall be secured in the slots by
slot wedges.
3.3.24.2 Field poles and pole shoes. Field poles and pole shoes shall not be secured by dowels or in such
manner as to prevent removal, replacement, and adjustment. The method of securing poles to the spider or shaft
shall result in a factor of not less than 2 based on the elastic limit of the material, at rated speed of the generator.
Integral laminated field poles, pole shoes, and spiders for salient-pole generators shall be optional for generators
rated 1,000 kilowatts and less. Two-pole generators shall be integral shaft-field pole machines.
3.3.24.3 Field coils. Field coils shall be form-wound. This shall not preclude the use of a salient-pole piece as
the form. Field coils of the same type or one design of machines shall be interchangeable in accordance with
MIL-E-917. The coils shall be secured so that they cannot become loosened or damaged by vibration, or produce
vibration by a slight shifting in coil position. Like coils of the same polarity shall be series-connected with respect
to each other.
3.3.24.4 Damper bars. Damper bars (amortisseur) shall be interconnected between poles.
3.3.24.5 Shaft currents. The induction of voltages in the shaft shall be minimized by selection of a number of
slots per pole and a number of lamination segments per circle in relation to the pole. Bearings and bearing housings,
or both, for generators rated 500 kilowatts and more, shall be insulated to prevent induced shaft currents from
flowing through these components. The insulation shall be of the double or sandwich type so that insulation
integrity can be verified with the rotor connected to the prime mover and without disassembly. The insulation shall
be designed into the system to isolate the bearing housing from the frame. Insulation shall not be used on the shaft
to bearing surfaces.
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