MIL-PRF-27G
4.7.10.3 Saturating core power transformers. Saturating core power transformers should be tested at the limit of
their linear characteristics, using sine wave power sources at twice normal operating frequency. The test voltage shall
be applied to any winding sufficient to cause twice the normal peak-to-peak voltage appear across any winding.
4.7.11 Insulation resistance (see 3.13). Transformers and inductors shall be tested in accordance with method
302 of MIL-STD-202. The following details and exceptions shall apply:
a.
Test condition B for qualification inspection; and dc test potentials from 500 volts to 1,000 volts for
quality conformance inspection. However, for quality conformance inspection, rejection shall be based
on measurements made at 500 volts. For both qualification inspection and quality conformance
inspection, the test voltage will be 100 volts if the working voltage is less than 175 volts and 50 volts if
the working voltage is less than 25 volts.
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 (if cased) or to the normal mounting
means (if uncased) and to the core (if accessible).
(2)
Between windings (for grade 5 units when mounting brackets or core are not accessible) - The
potential shall be applied between each winding and all other windings connected together.
The measurements shall be made at any temperature above 20°C and at ambient room humidity, but
rejections shall be based on measurements made at 25°C +10°C, -5°C and at a relative humidity not
greater than 80 percent.
4.7.12 Electrical characteristics (see 3.14). The electrical characteristics shall be determined by the tests specified
herein, as applicable (see 3.1). Electrical tests included herein do not embrace all of the electrical tests that may be
requested.
4.7.12.1 No load. Rated voltage at the frequency or frequencies specified (see 3.1) shall be applied to the primary
with the secondary or secondaries open circuited. The following shall be determined:
a.
No-load rms current (In1).
No-load power (Pn1).
b.
c.
Primary-tap and secondary rms voltages.
Center-tap voltage unbalanced in percent = [(V1 - V2)/V1] x 100
d.
The voltage unbalance shall be computed: V1 and V2 are the voltages of each part of the winding, and
V1 > V2.
4.7.12.1.1 For vibrator or invertor transformers. The transformers shall be connected to ac sources at the
specified frequency and voltage (see 3.1). The following shall be determined:
No-load true rms current (In1).
a.
b.
Primary tap and secondary true rms voltages.
c.
Voltage unbalance (when applicable) using the method specified in 4.7.12.1d.
4.7.12.2 Rated load.
4.7.12.2.1 Unrectified outputs. Unrectified output secondary voltages shall be measured with the transformer
primary excited at rated voltage at the specified frequency (see 3.1), and with rated rms load currents flowing in the
secondary windings.
4.7.12.2.2 Rectified outputs. Rms voltages at the secondary terminals shall be measured with the transformer
primary excited at rated voltage at the specified frequency, and with rated dc current flowing from a specified rectifier
and filter in a resistive load (see 3.1).
4.7.12.2.3 For vibrator or inverter transformers. The vibrator or inverter transformer shall be tested in the circuit or
simulated circuitry for which it is designed. The transformer primary shall be excited from the specified source. The
secondaries shall be loaded as specified. The following shall be determined:
a.
DC input voltage and current.
b.
Secondary true rms voltage and current, or dc voltage and current as applicable.
c.
Operating frequency and waveform characteristics (when specified).
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