MIL-DTL-28778A
3.6.2.2 Output voltage. The output voltage shall be 3750/6500 volts RMS nominal with 460 volts
RMS input across terminals 1 and 29, 2 and 30, 3 and 28.
3.6.2.3 Rated line current. The rated line current shall be 6.83 amps RMS per leg.
3.6.2.4 Working voltage. The working voltage shall be 13,600 volts peak.
3.6.2.5 Load. The load shall be a full wave silicon bridge rectifier with a choke input filter. Output of
supply shall be 8.5 kVDC at 8 amps DC continuous. The transformer shall also be used to supply a half-wave, 3-
phase rectifier with a 4.5kVDC, 1.0 amp DC output.
3.6.3
Secondary number 2. Terminals S1, S2, S3, and S0, wye connected.
3.6.3.1 Transformer impedance. The impedance from primary to secondary No. 2 shall be no
greater than 10 percent.
3.6.3.2 Output voltage. The output voltage shall be 640/1100 volts RMS nominal with 460 volts RMS
across terminals 1 and 29, 2 and 30, 3 and 28.
3.6.3.3 Rated line current. The rated line current shall be 7.67 amps RMS per leg.
3.6.3.4 Working voltage. The working voltage shall be 2860 volts peak.
3.6.3.5 Load. The load shall be a full wave silicon bridge rectifier with a choke input filter. Output of
supply shall be 1.5 kVDC at 8.0 amps DC continuous.
excitation current, core loss and impedance measurements shall not vary more than 5 percent of the initial
measurement values of these characteristics.
3.7 Terminals. The terminals shall be corona-free high voltage ceramic bushing for secondary.
Primary terminals shall be stud type, ceramic bushings.
3.7.1 Terminal strength. When transformers are tested as specified in 4.6.3, there shall be no
evidence of loosening or rupturing of the terminals, or other mechanical damage. There shall be no rotation of the
terminals.
3.8 Dielectric withstanding voltage. When transformers are tested as specified in 4.6.4, there shall be
no evidence of arching, flashover, break-down of insulation, or damage.
3.9 Induced voltage. When transformers are tested as specified in 4.6.5, there shall be no evidence
of continuous arching or breakdown of insulation, nor shall there be any abrupt changes in the input current.
3.10 Insulation resistance. When measured as specified in 4.6.6 the minimum insulation resistance
shall be 10,000 megohms.
3.11 Fungus. All external materials shall be nonnutrient to fungus growth or shall be suitably treated
to retard fungus growth. The manufacturer shall certify that all external materials are fungus resistant (see 4.6.7), or
shall perform the test specified in 4.6.7. There shall be no evidence of fungus growth on the external surfaces.
shall be no corona present, or the extinction voltage shall not be less than 7750 volts for secondary number 1 and
1310 VRMS for secondary number 2.
3.13 Temperature rise. When transformers are tested as specified in 4.6.9, the temperature rise of
any winding shall not exceed 55ºC maximum above a 50ºC ambient, and there shall be no evidence of physical or
electrical damage.
3.14 Winding continuity. When transformers are tested as specified in 4.6.10, all windings shall be
electrically continuous.
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