ASTM D2029-97(2008)
(Test Method)Standard Test Methods for Water Vapor Content of Electrical Insulating Gases by Measurement of Dew Point
Standard Test Methods for Water Vapor Content of Electrical Insulating Gases by Measurement of Dew Point
SIGNIFICANCE AND USE
Certain gases have excellent dielectric and electric arc interruption characteristics which make their use in electrical installations very desirable.
Water content, as the test parameter, is of great importance in determining the dielectric effectiveness of the gas. Under certain conditions, water may condense and become a conducting liquid resulting in a catastrophic dielectric breakdown of the insulation. The water content of these insulating gases as expressed by dew point is listed in Specifications D 1933, D 2473, and D 3283.
Once the dew point is determined, a conversion to moisture content may be performed using Table 1. Once moisture content is known, the lowest temperature at which gas insulated equipment can be safely operated can usually be determined by reviewing manufacturers' specifications for the equipment.
The dew point of the test gas is independent of the gas temperature but does depend on its pressure. Many moisture measurement test instruments are sensitive to pressure, and display moisture values at the instrument inlet pressure and not necessarily at the pressure of the system being sampled. It is therefore important to account for this condition to avoid serious measurement errors.
TABLE 1 Relationship Between Dew Point and Moisture Content of Gases
Note—With a known dew point which is indicated by the dew point indicator or recorder, the moisture content can be read directly from the table. The table shows the amount of water in air or other gas at various dew points at a pressure of 1 atm (14.7) psi. Dew PointMoisture ContentDew PointMoisture Content °C°Flb/1000
ft3mg/LvolumeA
percent°C °Flb/1000
ft3mg/LvolumeA
percent 50 122.05.1682.712.2−16 3.20.0791.27 0.149 49 120.24.9278.911.6−171.40.0721.16 0.136 48 118.44.6975.111.0−18 −0.40.0661.06 0.123 47 116.64.4871.910.5−19 −2.20.0600.965 0.112 46 114.84.2668.49.95−20 −4.00.0550.882 0.102 45113.04.06 65.09.45−21−5.80.0500.8090.093 44111.23.88 62.18.99−22−7.60.0460.7330...
SCOPE
1.1 These test methods describe the determination of the water vapor content of electrical insulating gases by direct or indirect measurement of the dew point and the calculation of the water vapor content.
1.2 The following four test methods are provided:
1.2.1 Method A describes the automatic chilled mirror method for measurement of dew point as low as − 73°C (−99°F).
1.2.2 Method B describes the manual chilled mirror or dew cup method for measurement of dew point as low as − 73°C (−99°F).
1.2.3 Method C describes the adiabatic expansion method for measurement of dew point as low as − 62°C (−80°F).
1.2.4 Method D describes the capacitance method for measurement of dew point as low as − 110°C (−166°F).
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific warnings, see 8.1.1, 9.2, 10.1.2 and 10.2.5.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D2029 − 97 (Reapproved 2008)
Standard Test Methods for
Water Vapor Content of Electrical Insulating Gases by
Measurement of Dew Point
This standard is issued under the fixed designation D2029; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 3. Terminology
1.1 These test methods describe the determination of the 3.1 Definitions:
water vapor content of electrical insulating gases by direct or
3.1.1 dew point, n—the temperature to which a gas must be
indirect measurement of the dew point and the calculation of
cooledatconstantpressureandconstantwatervaporcontentin
the water vapor content.
order for saturation to occur. Any further cooling usually
results in formation of the first drop of dew.
1.2 The following four test methods are provided:
1.2.1 Method A describes the automatic chilled mirror
3.1.2 hygroscopic, adj—readily taking up and retaining
method for measurement of dew point as low as−73°C
moisture.
(−99°F).
1.2.2 Method B describes the manual chilled mirror or dew
4. Summary of Test Methods
cup method for measurement of dew point as low as−73°C
4.1 Method A—The automatic chilled mirror method uses
(−99°F).
the chilled mirror dew point condensation principle to deter-
1.2.3 Method C describes the adiabatic expansion method
mine the water vapor content in gas mixtures. An internal
for measurement of dew point as low as−62°C (−80°F).
mirror, which is in the path of the test gas, is automatically
1.2.4 Method D describes the capacitance method for mea-
cooled. Internal electronics sense the presence of moisture on
surement of dew point as low as−110°C (−166°F).
the mirror. The device then automatically brings itself to
1.3 This standard does not purport to address all of the
equilibrium and provides a direct reading of dew point tem-
safety concerns, if any, associated with its use. It is the
perature.
responsibility of the user of this standard to establish appro-
4.2 Method B—This method uses the same basic condensa-
priate safety and health practices and determine the applica-
tion principle in 4.1; however, the manual chilled mirror
bility of regulatory limitations prior to use. For specific
method uses a mixture of acetone and ice or other cooling
warnings, see 8.1.1, 9.2, 10.1.2 and 10.2.5.
media to manually chill the dew cup polished surface which
acts as the mirror.
2. Referenced Documents
4.3 MethodC—Adiabaticexpansionusesaprocessinwhich
2.1 ASTM Standards:
the test gas is cooled rapidly to determine dew point tempera-
D1933Specification for Nitrogen Gas as an Electrical Insu-
ture.Thisrapidexhaustingofthetestgastoatmosphereresults
lating Material
in an expansion and cooling of the gas. If the cooling is
D2472Specification for Sulfur Hexafluoride
sufficient to reduce the temperature of the gas to or below the
D3283Specification for Air as an Electrical Insulating Ma-
dew point, water vapor will condense out in the form of a fine
terial
mist or fog. Successive trials will determine the minimum
initialpressurethatwillproduceafog.Fromthis,thedewpoint
temperature can be calculated.
These test methods are under the jurisdiction of ASTM Committee D27 on
4.3.1 The relationship between pressure and temperature
Electrical Insulating Liquids and Gasesand are the direct responsibility of Subcom-
mittee D27.07 on Physical Test.
during adiabatic expansion is as follows:
Current edition approved Dec. 1, 2008. Published December 2008. Originally
@K21/K#
T 5 T P /P
@ #
approved in 1964. Last previous edition approved in 2003 as D2029–97 (2003). F I F I
DOI: 10.1520/D2029-97R08.
2 where:
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contactASTM Customer Service at service@astm.org. ForAnnual Book ofASTM
K = ratio of specific heats for a given gas,
Standards volume information, refer to the standard’s Document Summary page on
T = final temperature,
F
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2029 − 97 (Reapproved 2008)
T = initial temperature,
I
D2029 − 97 (2008)
6.3.1 For MethodsA, B, and C, the relatively large volume
P = final pressure, and
F
of gas required to deposit sufficient water vapor to create the
P = initial pressure.
I
“dew”.
4.4 Method D—The capacitance method uses a moisture
6.3.2 For Methods A, B, and C, that under very dry
sensor, typically aluminum oxide or silicon oxide, which
condition,thepossibilityexiststocondensethetestgaspriorto
changes its electrical output with the amount of water vapor to
deposition of moisture on the mirror.
which it is exposed.
6.3.3 For Methods A, B, C, and D, that the measuring
system (instrument and tubing) must not entrain moisture. If
5. Significance and Use
any moisture is entrained, several hours may be required for
the gas being measured to come into equilibrium with the
5.1 Certain gases have excellent dielectric and electric arc
measuring system.
interruption characteristics which make their use in electrical
6.3.4 ForMethodsBandC,thesensitivityofthehumaneye
installations very desirable.
in determining exactly when the dew first forms.
5.2 Water content, as the test parameter, is of great impor-
tance in determining the dielectric effectiveness of the gas. 7. General Requirements
Under certain conditions, water may condense and become a
7.1 Methods A, B, and C—Any properly constructed dew
conducting liquid resulting in a catastrophic dielectric break-
point apparatus may be used that provides a means to satisfy
down of the insulation. The water content of these insulating
the following basic requirements:
gases as expressed by dew point is listed in Specifications
7.1.1 Control the flow of gas entering and leaving the
D1933, D2472, and D3283.
apparatus while the apparatus is at a temperature at least 2°C
(3.6°F) above the dew point of the gas.
5.3 Once the dew point is determined, a conversion to
7.1.2 Control the cooling rate of a chamber in the apparatus
moisture content may be performed using Table 1. Once
through which the flowing gas passes to a temperature low
moisturecontentisknown,thelowesttemperatureatwhichgas
enough to cause water vapor to condense from the gas.
insulated equipment can be safely operated can usually be
7.1.3 Detectthedepositionofdewonthecoldportionofthe
determined by reviewing manufacturers’ specifications for the
apparatus and measure the temperature at which dew is
equipment.
formed.
5.4 The dew point of the test gas is independent of the gas
7.1.4 Ensure that the test gas is at or near atmospheric
temperature but does depend on its pressure. Many moisture
pressure and is isolated from contamination from other gases.
measurement test instruments are sensitive to pressure, and
7.2 Method D—Any properly constructed capacitive type
displaymoisturevaluesattheinstrumentinletpressureandnot
moisture sensor may be used that provides a means to satisfy
necessarily at the pressure of the system being sampled. It is
the following basic requirements:
therefore important to account for this condition to avoid
7.2.1 Expose the sensor to a gas that is at a temperature at
serious measurement errors.
least 10°C (18°F) above the dew point of the gas.
7.2.2 Measurethepartialvaporpressureofwaterinagasby
6. Interferences
means of a capacitive type sensor.
6.1 Tubing:
7.3 These test methods provide for several techniques, each
6.1.1 Most new metal tubing contains oil deposits on the
utilizing different types of apparatus for measuring dew point.
interior walls due to the manufacturing process. This residue
The techniques in these test methods are provided for general
should be removed before using these lines for gas sampling.
information and are not intended as a substitute for manufac-
6.1.2 Tubing should be free of leaks, since even a pinhole
turer’s instructions. When using any instrument, the manufac-
leak will result in a false indication (higher dew point), due to
turer’s instructions should be followed to ensure proper and
the partial pressure of water vapor in the atmosphere.
safe operation.
6.1.3 Whenthegasbeingtestedisextremelydry[dewpoint
8. Apparatus
below approximately−40°C (−40°F)], results can be mislead-
ing until the moisture adsorbed in the system (tubing, 8.1 General:
regulators,etc.)hasbeenremovedbypurgingwiththetestgas.
8.1.1 Tubing—Although not true of all applications, stain-
At this point, all moisture present within the system should be less steel, glass, and nickel alloy tubing are the best possible
due to that contained in the test gas.
nonhygroscopic materials and should be used for low dew
point applications−18 to−73°C (0 to−100°F). Copper and
6.2 When testing gases that contain readily liquefiable
aluminum alloys, as well as stabilized polypropylene tubing,
impurities, it must be kept in mind that the dew point that is
are acceptable above−29°C (−20°F) dew point. (Warning—
measured by condensation type instruments may be due to
All materials will adsorb moisture to some extent; therefore,
these impurities rather than to water. Under these conditions,
the internal surface of apparatus, tubing, and fittings should be
the measured dew point is not an indication of the water
minimized to enable the system to dry out more quickly and
content of the gas.
achieve equilibrium sooner. However, it should be noted that
6.3 Measurement of water vapor in very dry gases is when one switches from measurement of a high dew point to
complicated by four considerations, as follows: a lower dew point [that is, 0 to−60°C (32 to−76°F)] copper
D2029 − 97 (2008)
TABLE 1 Relationship Between Dew Point and Moisture Content of Gases
NOTE 1—With a known dew point which is indicated by the dew point indicator or recorder, the moisture content can be read directly from the table.
The table shows the amount of water in air or other gas at various dew points at a pressure of 1 atm (14.7) psi.
Dew Point Moisture Content Dew Point Moisture Content
A A
lb/1000 lb/1000
volume volume
°C °F mg/L °C °F mg/L
3 3
percent percent
ft ft
50 122.0 5.16 82.7 12.2 −16 3.2 0.079 1.27 0.149
49 120.2 4.92 78.9 11.6 −17 1.4 0.072 1.16 0.136
48 118.4 4.69 75.1 11.0 −18 −0.4 0.066 1.06 0.123
47 116.6 4.48 71.9 10.5 −19 −2.2 0.060 0.965 0.112
46 114.8 4.26 68.4 9.95 −20 −4.0 0.055 0.882 0.102
45 113.0 4.06 65.0 9.45 −21 −5.8 0.050 0.809 0.093
44 111.2 3.88 62.1 8.99 −22 −7.6 0.046 0.733 0.084
43 109.4 3.69 59.1 8.52 −23 −9.4 0.042 0.666 0.076
42 107.6 3.52 56.4 8.10 –24 −11.2 0.038 0.608 0.069
41 105.8 3.34 53.5 7.67 −25 −13.0 0.035 0.556 0.063
40 104.0 3.18 50.9 7.27 −26 −14.8 0.031 0.506 0.057
39 102.2 3.02 48.4 6.89 −26 −16.6 0.028 0.454 0.057
38 100.4 2.87 46.0 6.54 −28 −18.4 0.025 0.411 0.046
37 98.6 2.74 43.8 6.20 −29 −20.2 0.023 0.377 0.042
36 96.8 2.60 41.6 5.87 −30 −22.0 0.021 0.343 0.038
35 95.0 2.46 39.4 5.55 −31 −23.8 0.019 0.307 0.034
34 93.2 2.34 37.4 5.25 −32 −25.6 0.017 0.273 0.030
33 91.4 2.22 35.6 4.96 −33 −27.4 0.015 0.246 0.027
32 89.6 2.11 33.8 4.70 −34 −29.2 0.014 0.229 0.025
31 87.8 2.00 32.0 4.44 −35 −31.0 0.013 0.202 0.022
30 86.0 1.89 30.3 4.19 −36 −32.8 0.012 0.185 0.020
29 84.2 1.84 29.2 4.01 −37 −34.6 0.010 0.167 0.018
28 82.4 1.69 27.1 3.7 −38 −36.4 0.0093 0.149 0.016
27 80.6 1.60 25.7 3.52 −39 −38.2 0.0082 0.131 0.014
26 78.8 1.52 24.4 3.33 −40 −40.0 0.0074 0.119 0.0127
25 77.0 1.44 23.0 3.12 −41 −41.8 0.0068 0.107 0.0113
24 75.2 1.35 21.7 2.94 −42 −43.6 0.0060 0.096 0.0102
23 73.4 1.28 20.6 2.78 −43 −45.4 0.0054 0.086 0.0090
22 71.6 1.21 19.4 2.61 −44 −47.2 0.0047 0.076 0.0080
21 69.8 1.14 18.3 2.46 −45 −49.0 0.0042 0.068 0.0071
20 68.0 1.08 17.3 2.31 −46 −50.8 0.0038 0.061 0.0063
19 66.2 1.02 16.3 2.17 −47 −52.6 0.0034 0.054 0.0056
18 64.4 0.961 15.4 2.04 −48 −54.4 0.0031 0.049 0.0050
17 62.6 0.899 14.4 1.91 −49 −56.2 0.0027 0.043 0.0044
16 60.8 0.855 13.7 1.80 −50 −58.0 0.0024 0.038 0.0039
15 59.0 0.799 12.8 1.68 −51 −59.8 0.0021 0.034 0.0034
14 57.2 0.749 12.0 1.57 −52 −61.6 0.0019 0.030 0.0030
13 55.4 0.706 11.3 1.48 −53 −63.4 0.0017 0.027 0.0027
12 53.6 0.668 10.7 1.39 −54 −65.2 0.0014 0.023 0.0023
11 51.8 0.620 9.94 1.29 −55 −67.0 0.0013 0.021 0.0021
10 50.0 0.584 9.37 1.21 −56 −68.8 0.0011 0.018 0.0018
9 48.2 0.547 8.76 1.13 −57 −70.6 0.0010 0.016 0.0016
8 46.4 0.516 8.27 1.06 −58 −72.4 0.00087 0.014 0.0014
7 44.6 0.482 7.73 0.988 −59 −74.2 0.00075 0.012 0.0012
6 42.8 0.452 7.25 0.924 −60 −76.0 0.00069 0.011 0.0011
5 41.0 0.424 6.79 0.861 −61 −77.8 0.00059 0.0095 0.00092
4 39.2 0.399 6.36 0.804 −62 −79.6 0.00052 0.0083 0.00080
3 37.4 0.370 5.94 0.748 −63 −81.4 0.00046 0.0073 0.00070
2 35.6 0.346 5.55 0.696 −64 −83.2 0.00040 0.0064 0.00061
1 33.8 0.323 5.18 0.649 −65 −85.0 0.00035 0.0056 0.00053
0 32.0 0.302 4.84 0.602 −66 −86.8 0.00030 0.0048 0.00045
−1 30.2 0.280 4.49 0.556 −67 −88.6 0.00027 0.0043 0.00040
−2 28.4 0.258 4.14 0.511 −68 −90.4 0.00022 0.0036 0.00034
−3 26.6 0.238 3.81 0.470 −69 −92.2 0.00019 0.0031 0.00029
−4 24.8 0.220 3.52 0.431 −70 −94.0 0.00017 0.0027 0.00025
−5 23.0 0.202 3.24 0.396 −71 −95.8 0.00015 0.0024 0.00022
−6 21.2 0.186 2.98 0.364 −72 −97.6 0.00013 0.0021 0.00019
−7 19.4 0.171 2.74 0.333 −73 −99.4 0.00011 0.0018 0.00016
−8 17.6 0.158 2.53 0.306 −74 −101.2 0.00009 0.0015 0.00014
−9 15.8 0.145 2.32 0.280 −75 −103.0 0.00008 0.0013 0.00012
−10 14.0 0.134 2.14 0.257 −76 −104.8 0.00007 0.0011 0.00010
−11 12.2 0.122 1.96 0.235 −77 −106.6 0.00006 0.0010 0.00009
−12 10.4 0.113 1.81 0.215 −78 −108.4 0.00005 0.0008 0.00007
−13 8.6 0.103 1.65 0.196 −79 −110.2 0.00004 0.0007 0.00006
−14 6.8 0.095 1.52 0.179 −80 −112.0 0.00004 0.0006 0.00005
−15 5.0 0.086 1.38 0.163 −81 −113.8 0.00003 0.0005 0.00004
A
Vapor pressures in atmospheres at various dew points can be obtained by dividing the values for “volume percent’’ in this table by 100. Calculations for this table were
made by using the International Critical Table values for the vapor pressure of ice and liquid water. The vapor pressure of liquid water was used for values from 50 to 0°C.
The vapor pressure of ice was used from 0 to − 81°C.
D2029 − 97 (2008)
tubing might take1hor more to desorb the moisture from the
previous sample, whereas stainless steel will equilibrate in
approximately 10 min.)
8.1.2 Although not a requirement, the addition of a chart
recorder to various automated systems makes determining
when the syste
...
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