MIL-DTL-3124E(SH)
4.5 Examination. Each generator shall be thoroughly examined to ascertain that the material, workmanship,
and construction conform to this specification. The fit of parts shall be observed with particular reference to the
interchangeability of such parts as are likely to require replacement during the normal service life of the generator.
4.6 Test methods. Test methods shall be as specified (see 4.6.1 through 4.6.30). Measurements taken shall be
provided as specified in the contract or order. Digital data acquisition and computer analysis methods may be used
instead of manual calculations with approval from NAVSEA.
4.6.1 Electrical insulation. A sample coil or winding shall be provided (see 3.4.27). The sample shall be cut
open and examined for evacuation of all air and water, and the filling in of all interstices as approved by NAVSEA.
4.6.2 Air-gap measurements. The air-gap between the rotor and stator iron shall be measured for generators,
exciters, and permanent magnet alternators. The air-gap shall be measured by steel feelers or gauges. The
measurements shall be made at four radii (two horizontal and two vertical) at each end of the generator.
4.6.3 Resistance. The DC resistance of the stator and the rotor windings and the temperature at which they are
measured shall be taken.
4.6.4 Airborne and structureborne noise. When special noise limitations are required (see 3.3.23 and 6.2),
airborne and structureborne noise tests for generator sets shall be in accordance with MIL-G-3087, MIL-G-21296,
and MIL-G-22077, or applicable equipment specifications.
4.6.5 Vibration (internally excited). When a generator with a keyed coupling is tested prior to assembly of the
couplings on the shaft, the generator shall be balanced with one-half a standard key in the keyway, which shall
consist of a key of full length flush with the top of the keyway. When subjected to vibration tests, the rotor shall be
mounted in bearing brackets. The method of testing shall be in accordance with MIL-STD-167-1, Type II. A
vibration indicator, whereby vibrations of the amplitude of 0.0005 inch may be readily observed on a suitable scale,
may be used as a measuring device. Vibration tests shall be taken at no-load, rated speed, and at speed-load
conditions.
4.6.6 Dynamic balance. The actual unbalance shall be measured to ensure that the limits in accordance with
MIL-STD-167-1, Type II, are achieved. Calculated values based on vibration amplitudes and frequency shall be
optional as specified (see 6.2).
4.6.7 No-load, rated voltage saturation data. This test shall be performed in one of the following ways:
a. The generator shall be driven as a synchronous motor with varying field excitation. At the value of
minimum armature current, with rated voltage at rated frequency applied to the terminals, the voltage between
phases, watts input, field current, field voltage, and speed shall be measured. The generator shall run to allow stable
temperatures before readings are taken.
b. The generator shall be driven by any convenient prime mover and sufficient excitation shall be applied to
produce rated voltage. Readings of voltage between phases, field current, field voltage, and speed shall be taken.
The generator shall run to allow stable temperatures before readings are taken.
4.6.8 Lubrication. The lubricating system shall be observed when the generator is operating in a normal
horizontal position to determine whether lubrication is provided. For generators in the inclined positions, lubrication
shall be determined when the generator is operating with the prime mover as a unit. This test shall be observed
during the progress of the other tests, or as the circumstances warrant. The test may be made at any convenient
ambient temperature.
4.6.9 Overspeed. Each generator shall be subjected to an overspeed test at 25 percent greater than the normal
operating speed for a period of 5 minutes. Field excitation shall be applied to the field to produce rated voltage.
The speed shall be increased slowly until the generator reaches the maximum test speed. The generator shall be at
no-load condition. Checks shall be made for noise, mechanical balance, and smoothness of running during the test
and for evidence of distortion, damage, or noticeable change in the condition of any part after shutdown. No
attached rotating parts, such as welded fans and spiders, need to be tested for a greater overspeed.
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