FED-STD-228A
Method 6271.1
18 APRIL 2014
CAPACITANCE CHANGE WITH TIME IN WATER
1. SCOPE
1.1 This method is intended for use in determining the effect of moisture on moisture-resistant insulation
due to immersion in water for varying periods of time by measuring the changes in the dielectric constant
of the insulation.
2. SPECIMEN
2.1 The specimen should be a 15-foot length of the inspection unit from which any covering over the
insulation has been removed; or the specimen may be taken after vulcanization and prior to the
application of any covering.
3. APPARATUS
3.1 The apparatus shall be as follows:
3.1.1 A suitable capacitance bridge. The bridge shall be capable of measuring the capacitance with a
limit of error of 1 microfarad. It shall be capable of measuring the capacitance of a specimen one side of
which is grounded. Provisions shall be made for connecting and disconnecting the specimen at the
specimen end of the leads connecting the specimen to the bridge.
3.1.2 A water bath in which the specimen can be immersed.
4. PROCEDURE
4.1 Unless otherwise specified in the detail specification, the specimen shall be immersed in water at
room temperature not less than 21° C (70°F) for a period of 14 days.
4.2 Unless otherwise specified in the detail specification, readings shall be taken after 22, 166, and 334
hours of immersion in water at room temperature not less than 21°C (70°F).
4.3 The diameter of the specimen over the insulation and over the conductor shall be determined as
described in method 1011 and the value recorded as D and d respectively. The middle 10 feet of the
specimen shall be immersed in distilled water for the required period of time. A 2.5-foot portion of each
end of the specimen shall be kept well above the surface of the water as leakage insulation. The
capacitance of the insulation shall be determined at a frequency of either 1,000 or 60 cycles, using a
suitable capacitance bridge. The voltage impressed upon the conductor shall be sufficient to give the
required sensitivity of measurement, except that the impressed voltage on the conductor shall not be
greater than 40 volts per mil of insulation thickness. The specimen shall be immersed to the same depth
and the temperature of the water bath shall be the same at the time readings are taken after each
immersion period.
5. RESULTS
5.1 Calculation. The dielectric constant (K) of the insulation shall be calculated after each immersion
period as follows:
K = 13,600 C Log10 D/d
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