MIL-PRF-27G
4.7.23 Life (see 3.26). Unless otherwise specified (see 3.1), transformers with a rated output dissipation less than
0.8 watt shall be excited but not loaded. Transformers and inductors shall be subjected to 5 life cycles a week for a
minimum of 12 weeks (2,016 hours). Four of the cycles shall consist of 20 hours during which time the transformers
and inductors shall be operated at maximum operating temperature for the class, with loading equal to or greater than
rated ac and dc voltages and currents, and 4 hours at room ambient temperature without excitation. The fifth cycle of
the week shall be 68 hours at maximum operating temperature for the class with samples loaded as before and 4
hours without excitation at room ambient temperature. The electrical test circuit shall be devised so that an open
circuit (see 3.26) or short circuit (see 3.26) during the 5 life cycles shall be detected and the time of failure recorded.
For transformers only, the test may be performed with samples loaded back-to-back provided the above mentioned
loading requirements are met. This test may be performed at any ambient temperature provided that the maximum
operating temperature for the class is held within +10°C, -5°C and no drafts or varying air velocities are present. At the
option of the supplier, the test may be performed at 60 Hz for transformers rated at 50/60 Hz and at 400 Hz for
transformers rated at 360/400 Hz provided the primary voltage is increased to at least 1.1 times the rated voltage and
the maximum operating temperature for the class is attained. Upon completion of cycling after a minimum of 12
weeks, transformers and inductors shall be tested for insulation resistance (see 4.7.11), dielectric withstanding voltage
(at atmospheric pressure) (see 4.7.9.3) using 65 percent of initial test voltage, and induced voltage (see 4.7.10), using
a voltage sufficient to cause 1.3 times the rated voltage to appear across any winding. Samples shall also be
examined for evidence of physical and electrical damage.
Note: If a holiday should occur in any week while life tests are in progress, the four hour off cycle can be deleted for
that day. A maximum of two off cycles shall be allowed in any one week, when approved by the procuring activity.
4.7.24 Fungus (see 3.27). Unless certification is provided, transformers and inductors shall be tested in
accordance with method 508 of MIL-STD-810 (see 3.1).
4.7.25 Radiographic Inspection (Product level T only) (see 3.29). Transformers and inductors shall be tested in
accordance with Appendix B with three views of 90 degrees apart by X-ray, or 360 degree view by Vidicon. Use of
"real time" X-ray system capable of viewing through 360 degrees of rotation is encouraged.
5.
PACKAGING
5.1 Packaging requirements. For acquisition purposes, the packaging requirements shall be as specified in the
contract or purchase order. When actual packaging of material is to be performed by DoD personnel these personnel
need to contact the responsible packaging activity to ascertain requisite packaging requirements. Packaging
requirements are maintained by the Inventory Control Point's packaging activity within the Military Department or
Defense Agency, or within the Military Department's System Command. Packaging data retrieval is available from the
managing Military Department's or Defense Agency's automated packaging files, CD-ROM products, or by contacting
the responsible packaging activity.
6. NOTES
(This section contains information of a general or explanatory nature that may be helpful, but is not mandatory.)
6.1 Intended use. The transformers/inductors covered by this specification are military unique due to the fact
that these devices must be able to operate satisfactorily in military systems under the following demanding
conditions: -55°C to +170°C operating temperature range, 20 Gs of vibration, 100Gs of shock, 48 hours of salt
atmosphere, and 2,016 hours of endurance at the maximum temperature. In addition these military requirements are
verified under a qualification system. Commercial components are not designed to withstand these military
environmental conditions.
6.2 Acquisition requirements. Acquisition documents must specify the following:
a.
Title, number, date of the specification, applicable specification sheet, and the complete PIN (see
1.2.1).
b.
Packaging requirements (see 5.1).
100p29" style="font-size:11px">29
Downloaded: 2014-09-24T13:27Z
For Parts Inquires submit RFQ to Parts Hangar, Inc.
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business