MIL-DTL-3124E(SH)
4.6.26 Phase unbalance heating test. The generator shall be loaded with a single-phase load of 15 percent of
continuous rated current simultaneously with a balanced three-phase load. The total load shall be not less than
generator rated power factor, and the current in two phases shall be approximately (but not greater than) continuous
rated current. The single-phase load shall be a unity power factor load and shall not contain rotating equipment.
The test shall be continued until steady final temperatures have been attained in all parts of the generator. The
applicable requirements specified in 3.4.7.1 shall be met.
4.6.27 Negative-sequence impedance. A negative-sequence reactance (X2) and resistance (r2) test shall be
performed in accordance with MIL-STD-705, and the values calculated.
4.6.28 Voltage dip determination. The generator shall be driven by any convenient prime mover and operated
with its own exciter and regulator connected in a normal manner, except that the generator voltage regulator reactive
droop compensation shall be inoperative.
4.6.28.1 Load application. With the generator driven at a rated speed, voltage, and no-load, a balanced
three-phase impedance load, with an impedance of 2.0 per-unit and a power factor of 0 to 0.4 lagging, shall be
suddenly applied. One of the line-to-line voltages shall be measured by an oscilloscope. The voltage trace shall be
adjusted to not less than 80-millimeter peak-to-peak displacement for rated voltage and not less than 30 cycles
before the instant of load application to not less than 6 seconds of operation after the instant of application of load.
4.6.28.2 Calculation. From oscillograms, five peak-to-peak voltage measurements, not less than 5 cycles apart,
immediately preceding the instant of load application, shall be made and recorded. Similar measurements at least
every 5 cycles immediately following the load application shall also be made. The measurements shall be made by
measuring the peak-to-peak displacement between two lines drawn through the center of the light spots of the peaks
of the voltage waves which define the envelope of the voltage trace. With the average of the five measurements
before the load was applied taken as the reference reading or as unit voltage, the recorded readings after the load was
applied shall be divided by the reference reading to obtain the per-unit voltage during the voltage transient. The
per-unit voltages shall be plotted against time to a scale on graph paper. A curve shall be drawn through the plotted
points. The maximum voltage dip shall be the maximum deviation of the curve from the initial voltage.
4.6.29 EMI. EMI testing for generator sets shall be in accordance with MIL-G-3087, MIL-G-21296, or
MIL-G-22077, as applicable (see 3.4.24).
4.6.30 Short-circuited characteristic data. The following tests shall be made to calculate and plot the following
data (current against time) on logarithmic coordinate paper. Curves shall be based on a hot field:
a. Symmetrical rms current shall be obtained from a short-circuit, the generator operating at no-load, rated
voltage with automatic voltage regulation.
b. Maximum asymmetrical rms current shall be obtained from a short-circuit, the generator operating at
full-load, rated voltage with automatic voltage regulation.
4.7 Maintainability demonstration. When the generator is part of a generator set, a maintainability
demonstration test shall be conducted on the assembled generator set in accordance with MIL-G-3087,
MIL-G-21296, or MIL-G-22077, as applicable (see 6.3 and 6.6). The MTTR shall be as specified in 3.4.2.
Accessibility shall be as specified in 3.3.1.
4.7.1 Maintainability test conditions. The maintainability test shall be performed with the equipment or system
installed in a manner which simulates, to the satisfaction of the contracting activity, an actual shipboard installation.
The access envelope (see 3.3.1) shall be simulated with panels and screens. Test equipment, tools, repair parts, and
maintenance instructions shall be available for the performance of the tests. Test team, facilities, and support
material shall represent normal shipboard resources. Test mechanics shall be given no outside assistance.
4.7.2 Skill levels. The skill levels of contractor s shop personnel who perform the maintenance tasks of the
demonstration test shall be commensurate with Navy personnel who will maintain the generator.
4.7.3 Fault simulation. Simulation of faults or failures by introducing defective parts shall not be required.
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