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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
Table 7-3. Satisfactory power factors
d. Type of tests. Annual, comprehensive, and dis-
solved oil-in-gas tests are made on liquid insulation.
Mineral oil
RTemp Silicone
ANSI/IEEE C57.106 and ASTM D 117 cover accep-
0.005
0.005
0.005
tance, maintenance, and test requirements.
Distribution transformers
0.01. . . . . . . .
0.0 1
0.005
(1) Annual tests. Annual tests determine
whether the insulating liquid is in satisfactory con-
(3) Dissolved gas-in-oil tests. ASTM D 3612
dition or whether more comprehensive tests should
be made.
covers this test which analyzes the combustible gas
(a) Dielectric breakdown. The dielectric
liberated by normal use of insulating liquid. The
breakdown voltage test is covered in ASTM D 877.
dissolved gases are extracted from an oil sample. A
The minimum acceptable breakdown values are 22
portion of the gases are then subjected to chromato-
kV for oil and 26 kV for RTemp and silicone.
graphic analysis. This analysis determines the ex-
(b) Acidity. The acidity test is covered in
act gases present and the amount of each. Different
ASTM D 1534. This test indicates how much the oil
types of incipient faults have different patterns of
has oxidized. The maximum permissible neutraliza-
gas evolution. With this test the nature of the prob-
tion number is 0.4 for oil, 0.5 for RTemp, and 0.01
lems can often be diagnosed, utilizing data from
for silicone.
IEEE 104.
(c) Color. The color test is covered in ASTM D
e. Reconditioning and replacement of insulating
Liquids. If any of the tests indicate that an insulat-
1524. New oil is clear, while a dark oil indicates
contamination. The maximum acceptable "color
ing liquid is not in satisfactory condition, it may be
number" is 4 for oil and 1.5 for RTemp.
restored by reconditioning, reclaiming, or it can be
(2) Comprehensive tests. Comprehensive tests
completely replaced. Reconditioning is the removal
include a power factor test using an ASTM D 924
of moisture and solid materials by mechanical
test cell, and an interfacial tension (IFT) test in
means such as filter presses, centrifuges, or vacuum
dehydrators. Reclaiming is the removal of acidic
accordance with ASTM D 971 or ASTM D 2285. A
liquid at 20 degrees C, with a power factor as given
and colloidal contaminants, and products of oxida-
tion, by chemical and absorbent means. These in-
in table 7-3, is considered satisfactory. If the value
is above 0.5 percent investigate. If the value is
clude processes involving Fuller's earth, either
alone or in combination with other substances. Re-
above 2 percent, replace or recondition. The IFT will
vary dependent upon the liquid used, but values
placing the liquid involves draining, flushing, test-
ing, and proper disposal of materials removed. It is
below 40 dynes per centimeter for oil, 30 dynes per
centimeter for RTemp, and 21 dynes per centimeter
recommended that these procedures be done by con-
tract personnel who have the necessary experience
for silicone probably indicate that reconditioning is
advisable.
and equipment.
7-8





 


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