MIL-PRF-21038F
The transformer shall be conditioned for at least 8 hours at temperature (t) in a location free from drafts before
resistance (r) is measured. Rated voltage shall be applied to the primary with the specified loads across the
secondaries (see 3.1). Transformers shall be operated until two consecutive resistance readings on the highest
resistance winding, taken 30 minutes apart, are the same. The resistance measurements (R) shall be made as
soon as possible, but not more than 20 seconds after shut-off of power. The transformers shall be examined for
evidence of physical damage.
4.7.17.1 Test procedure. The transformers shall be supported centrally by means of two low-thermal-
conductivity cleats (3 inches (76 mm) in height) and a test cabinet of low thermal capacity and shall be free of
test area drafts and direct thermal radiation. The cabinet used shall provide a minimum clearance of 8 inches
(203 mm) between the sides and top of the transformer under test and the internal planes of the test cabinet.
Any closure approved by the Government which gives equivalent performance may be substituted for the
above.
5. PACKAGING
5.1 Packaging. For acquisition purposes, the packaging requirements shall be as specified in the contract or
order (see 6.2). When packaging of materiel is to be performed by DoD or in-house contractor personnel, these
personnel need to contact the responsible packaging activity to ascertain packaging requirements. Packaging
requirements are maintained by the Inventory Control Point's packaging activities within the Military Service or
Defense Agency, or within the military service's system commands. 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 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 +130°C operating temperature range, 15 gravity units of vibration, 100 gravity units of
shock. 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, and date of the specification, applicable specification sheet, and the complete PIN (see
3.1).
b.
Issue of DoDISS to be cited in the solicitation, and if required, the specific issue of individual
documents referenced (see 2.1).
c.
Packaging requirements (see 5.)
6.3 Qualification. With respect to products requiring qualification, awards will be made only for
products that are, at the time of award of contract, qualified for inclusion in Qualified Products List
QPL No. 21038 whether or not such products have actually been so listed by that date. The attention
of the contractors is called to these requirements, and manufacturers are urged to arrange to have
the products that they propose to offer to the Federal Government tested for qualification in order that
they may be eligible to be awarded contracts or orders for the products covered by this specification.
Information pertaining to qualification of products may be obtained from DSCC-VQP, P. O. Box 3990,
Columbus, Ohio 43216-5000 or mailto:vqp.re@dla.mil.
6.4 Maximum operating temperature. The maximum operating temperature is the same as the allowable
temperature rise plus the maximum ambient temperature for the device. Accordingly, temperature rise is the
allowable temperature differential between the ambient and maximum operating temperature for a given
insulation for a specified life. For example, a device has a maximum operating temperature designation of
105°C with a temperature rise of 20°C. Then this same transformer could operate in an ambient as high as
85°C (85°C + 20°C = 105°C).
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