MIL-DTL-3124E(SH)
4.6.13.3 Measurement of the ambient temperature. Measurement of ambient temperature shall be as specified
in 4.6.13.3.1 through 4.6.13.3.4.
4.6.13.3.1 Ambient temperature. A generator may be tested at any convenient ambient temperature above
50 °F (10 °C); however, the maximum temperature rise specified herein shall not be exceeded. Heat runs shall not
be undertaken on generators which have recently been brought from a place varying in temperature by 9 °F (5 °C) or
more from that in which the test is to be made, or where the temperature of the room in which the generator under
test has stood varied 9 °F (5 °C) or more during the preceding 2-hour period.
4.6.13.3.2 Temperature variance during test. Conditions in the testing room shall be such that the ambient
temperature will not vary greatly during test. A variation of 18 °F (10 °C) or more during a period of 6 hours, or a
proportional change for runs of shorter durations, shall not be exceeded. If the ambient temperature is irregular
during the run or changes rapidly at the end, the test shall be repeated.
4.6.13.3.3 Temperature sensors. The ambient temperature shall be measured by two or more temperature
sensors placed at different points around (and on a level with) the generator shaft, and at distances 3 to 6 feet from
the generator. The ambient temperature sensors shall be protected from drafts, heat radiation, equipment under tests,
or outside sources. The sensors shall be inserted in heavy oil-filled cups of not less than 1 inch in external diameter
and 2 inches in height.
4.6.13.3.4 Ambient temperature readings. The value to be adopted for the ambient temperature during the tests
shall be the readings of several temperature sensors, placed as specified (see 4.6.13.3.3), and taken at four equal
intervals of time during the last quarter of the test. During the first part of the heat run, temperature sensor readings
shall be taken at ½-hour intervals.
4.6.13.4 Method of measuring temperature. Temperature rise shall be measured as specified in 4.6.13.4.1
through 4.6.13.4.4.
4.6.13.4.1 Temperature rise. Except as specified herein, the method of measuring temperature rise shall be
optional. In determining temperature rise, correction shall not be made for barometric pressure, humidity, or
deviations of the recorded ambient temperature from the standard ambient temperature of reference. Only one
method of temperature determination shall be required for any particular part. Temperature rise for rotating fields
shall be measured in accordance with Method 2 of MIL-E-917, and bearings and mechanical parts shall be measured
in accordance with Method 1 of MIL-E-917.
4.6.13.4.2 Temperature sensors. When the temperature sensors are furnished for permanent bearing
measurements in the case of ring and disk lubrication, additional temperature sensor measurements shall not be
taken. When test temperature sensors are necessary, the temperature of the oil shall be taken by the temperature
sensor inserted in the inspection hole at the top of the bearing cap and touching the bearing shell.
4.6.13.4.3 Forced lubrication. For forced lubrication, the maximum temperature rise of the bearing shall be
taken as the difference between the temperature of the entering oil adjacent to the bearing pedestal and the oil
leaving the bearing pedestal, as determined by temperature sensors in the oil feed and drain lines.
4.6.13.4.4 Shutdown temperature. For shutdown, preheated temperature sensors shall be placed on the rotor
core and windings. Precautions shall be taken to reduce to a minimum the period of time elapsing between the
stopping of the machine and application of the temperature sensors. A curve shall be plotted with temperature
readings as ordinates and time as abscissa. That portion of the linear curve, starting where successive readings show
decreasing temperatures, shall be extrapolated back to the instant of shutdown. The temperature at the instant of
shutdown as determined in this manner shall be considered the shutdown temperature.
4.6.14 Insulation resistance (hot). Immediately following the heat run, measurements of insulation resistance
shall be taken as specified in 4.6.10.
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