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Impedance voltage and impedance watts |
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|  MIL-T-15108C(NAVY)
4.6.4 Impedance voltage and impedance watts.
Either the primary or the secondary
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winding shall be short-circuited and voltage at rated frequency applied to the other winding
and adjusted to circulate rated currents in the windings. With current and frequency
adjusted to rated values shown on the applicable drawing, simultaneous readings shall be
taken on the ammeter, voltmeter, wattmeter, and frequency meter. Temperature of the windings
during this test shall be determined.
4.6.5 Losses.
4.6.5.1 No-load losses. No-load losses shall be accurately determined. Rated voltage
shall be applied to either the primary or secondary windings. The frequencies shall be
60 Hz. Simultaneous readings shall be made of frequency, voltage, watts (low pf wattmeter),
and amperes. Actual design value appears on the drawings. No-load loss for transformers of
the same size and design may exceed the value shown on the drawing by 10 percent, but shall
not exceed the maximum allowable no-load losses specified in table II.
4.6.5.2 Total losses. Total losses shall be determined from the data obtained in the
impedance watts test and no-load loss test. Actual design value appears on the drawings.
Total loss for transformers of the same size, design, and type may exceed the value for
full-load loss watts shown on the drawing by 6 percent, but shall not exceed the value for
full-load losses specified in table II.
4.6.6 Exciting current. Exciting current shall be determined during the no-load loss
test and shall not exceed the maximum allowable value of exciting current specified in
table II.
4.6.7 Regulation. The regulation of a transformer shall be determined by calculation
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based on the measured values of impedance volts and impedance watts, corrected to 75C.
Either of the following formulae may be used in the calculation of the regulation:
Formula I:
Formula II:
Where:
cos 0 = power factor of load
=
P
=
q
negative phase angle of load current
impedance angle of transformer
r = resistance factor = impedance loss in kW
rated kVA
z = impedance factor = r/cos
x = reactance factor = +
2 2- r2
a=
The quantities of regulation are on a per unit basis so that the result must be multiplied
by 100 to get the regulation in percent.
4.6.8 Heating.
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4.6.8.1 General. Heating tests on transformers shall be made under conditions
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equivalent to normal operating conditions, that is, rated voltage, rated frequency, rated
current, and the duty specified. The test methods to be employed and the precautions to
be observed shall be as specified in 4.6.8.2 through 4.6.8.5.
The heating test shall be made only on the completely
4.6.8.2 Assembly of transformer.
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assembled transformer.
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