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MIL-PRF-27 Transformers And Inductors \(Audio, Power, And High-Power Pulse\), General Specification ForThis specification covers the general requirements for power transformers, power inductors, audio transformers, audio inductors, high power pulse transformers, charging inductors, saturable transformers and saturable inductors for use in electronic and communication equipment. This specification covers transformers and inductors weighing 300 pounds or less or having root-mean-square \(rms\) test-voltage ratings 0f 50,000 volts or less, and also high-power pulse transformers where the peak pulse power is greater than 5 watts. Transformer and inductor assemblies incorporating any other active or passive components do not come within the scope of this specification.

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MIL-PRF-27G

TABLE VI. Qualification inspection for transformers and inductors similar

to transformers and inductors that have been qualified.

Inspection

Requirement

Method

paragraph

Visual and mechanical examination

(external)- - - - - - - - - - - - - - -

3.1, 3.3 to 3.3.3.3 incl., 3.4.1, 3.4.3 to 3.4.3.3

4.7.1.1

incl., 3.4.5, 3.4.6, 3.4.8, 3.30 and 3.32

Dielectric withstanding voltage:

At atmospheric pressure- - - - - - - -

3.11

4.7.9.1

At barometric pressure (when

applicable) - - - - - - - - - - - - - - -

3.11

4.7.9.2

Induced voltage- - - - - - - - - - - - - - -

3.12

4.7.10

Insulation resistance- - - - - - - - - - - -

3.13a

4.7.11

Electrical characteristics - - - - - - - - -

3.14

4.7.12

Corona discharge (when specified) -

3.16

4.7.14

Temperature rise (1 sample unit) - - -

3.15

4.7.13

Overload - - - - - - - - - - - - - - - - - - - -

3.23

4.7.21

Dielectric withstanding voltage:

At reduced voltage - - - - - - - - - - -

3.11

4.7.9

Induced voltage- - - - - - - - - - - - - -

3.12

4.7.10

Insulation resistance- - - - - - - - - - -

3.13a

4.7.11

Winding continuity - - - - - - - - - - - -

3.20

4.7.18

Visual and mechanical examination

(external) - - - - - - - - - - - - - - - - -

3.1, 3.3 to 3.3.3.3 incl., 3.4.1, 3.4.3 to 3.4.3.3

4.7.1.1

incl., 3.4.5, 3.4.6, 3.4.8, 3.30 and 3.32

4.6 Conformance inspection.

4.6.1 Inspection of product for delivery

4.6.1.1 Product level C. Inspection of product for delivery shall consist of group A for product level C. (see

4.6.1.4.1)

4.6.1.2 Product levels M and T. Inspection of product for delivery shall consist of groups A and applicable group B

inspections. Product level T transformers and inductors shall not be delivered until they have successfully completed

group A and applicable group B inspections. Unless otherwise specified, product level M transformers or inductors

may be delivered after sample units have passed group A inspection prior to sample units completing applicable group

B inspection (see 4.6.1.5).

4.6.1.3 Inspection and Production lot.

4.6.1.3.1 Inspection lot. An inspection lot shall include completely assembled transformers or inductors of the

same grade, class, specification sheet, and electrical characteristics, manufactured under essentially the same

conditions and having similar construction and materials, may be combined to form a lot. (Similar construction and

materials shall be construed to include differences that will not affect test results.) For product level T transformers or

inductors, an inspection lot shall consist of one production lot.

4.6.1.3.2 Production lot. A production lot shall consist of all transformers and inductors covered by a single

specification sheet and single PIN. Manufacture of all parts in the lot shall have been started, processed, assembled,

and tested as a group. Lot identity shall be maintained throughout the manufacture cycle.

4.6.1.4 Group A inspection.

4.6.1.4.1 Product level C. The contractor shall establish and maintain an inspection system to verify the

transformer/inductor meet the electrical requirements, and visual/mechanical requirements. In-line or process control

may be part of such a system. The inspection system shall also include criteria for lot rejection and corrective actions.

NOTE: Since the product level C transformer/inductor is the product level M design without the mandatory government

conformance inspection, this product is still expected to meet the environmental qualification type requirements (e.g.,

moisture resistance, thermal shock, shock, vibration, etc.).

4.6.1.4.1 Product level M and T. Group A inspection shall consist of the applicable inspections specified in

Table VII, in the order shown.

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