MIL-DTL-28778A
4.6.5 Induced voltage (see 3.9). Transformers shall be subjected to a voltage sufficient to cause
twice the rated voltage to appear across any winding. The test voltage shall be applied to any winding. Windings
should be grounded as they would be in service. The test frequency shall be as selected by the manufacturer and
shall be remote from any resonant frequency.
of MIL-STD-202. The following details and exceptions shall apply:
(a) Test-condition letter B
(b) Points of measurement:
(1) Winding to case or core The potential shall be applied between each winding and the case
or core with all windings not under test grounded to the case. The measurements may be
made at any temperature above 20ºC and at ambient room humidity, but rejections shall be
based on measurements made at 25º + 10ºC, -5ºC and at a relatively humidity not greater
than 80 percent.
(c) Electrification time 1 minute maximum.
4.6.7 Fungus (see 3.11). Unless certification is provided, transformers shall be tested in accordance
with method 508 of MIL-STD-810.
4.6.8 Corona (3.12). The transformer shall be tested for corona using the applicable test circuit (see
figure 3) and in accordance with the following:
4.6.8.1 Secondary number 1. Test for intra-winding insulation with the following sequential
conditions, increase output voltage to 9050 VRMS. If no corona is present, then unit is acceptable. If corona occurs,
reduce output voltage until corona is extinguished. Extinction voltage shall be 7750 volts minimum. The test shall be
performed 3 times, one with each of terminals R1, R2 and R3 grounded in turn.
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