ASTM D2029-97

Standard Test Methods for Water Vapor Content of Electrical Insulating Gases by Measurement of Dew Point

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 precautions, see 8.1.1, 9.2, 10.1.2 and 10.2.5.

General Information

• Status: Historical
• Publication Date: 09-Apr-1997
• ICS: 29.040.20 - Insulating gases
• Technical Committee: D27 - Electrical Insulating Liquids and Gases
• Drafting Committee: D27.07 - Physical Test

Relations

• Replaced By: ASTM D2029-97(2003) - Standard Test Methods for Water Vapor Content of Electrical Insulating Gases by Measurement of Dew Point
• Effective Date: 10-Apr-1997
• Referred By: ASTM D3283-98(2020) - Standard Specification for Air as an Electrical Insulating Material
• Effective Date: 10-Apr-1997
• Referred By: ASTM D2472-15 - Standard Specification for Sulfur Hexafluoride
• Effective Date: 10-Apr-1997
• Referred By: ASTM D1933-03(2017) - Standard Specification for Nitrogen Gas as an Electrical Insulating Material
• Effective Date: 10-Apr-1997

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 2029 – 97
Standard Test Methods for
Water Vapor Content of Electrical Insulating Gases by
Measurement of Dew Point
This standard is issued under the fixed designation D 2029; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 3.1.1 dew point,, n—the temperature to which a gas must be
cooled at constant pressure and constant water vapor content in
1.1 These test methods describe the determination of the
order for saturation to occur. Any further cooling usually
water vapor content of electrical insulating gases by direct or
results in formation of the first drop of dew.
indirect measurement of the dew point and the calculation of
3.1.2 hygroscopic,, adj—readily taking up and retaining
the water vapor content.
moisture.
1.2 The following four test methods are provided:
1.2.1 Method A describes the automatic chilled mirror
4. Summary of Test Methods
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-
1.2.2 Method B describes the manual chilled mirror or dew
mine the water vapor content in gas mixtures. An internal
cup method for measurement of dew point as low as − 73°C
mirror, which is in the path of the test gas, is automatically
(−99°F).
cooled. Internal electronics sense the presence of moisture on
1.2.3 Method C describes the adiabatic expansion method
the mirror. The device then automatically brings itself to
for measurement of dew point as low as − 62°C (−80°F).
equilibrium and provides a direct reading of dew point tem-
1.2.4 Method D describes the capacitance method for mea-
perature.
surement of dew point as low as − 110°C (−166°F).
4.2 Method B—This method uses the same basic condensa-
1.3 This standard does not purport to address all of the
tion principle in 4.1; however, the manual chilled mirror
safety concerns, if any, associated with its use. It is the
method uses a mixture of acetone and ice or other cooling
responsibility of the user of this standard to establish appro-
media to manually chill the dew cup polished surface which
priate safety and health practices and determine the applica-
acts as the mirror.
bility of regulatory limitations prior to use. For specific
4.3 Method C—Adiabatic expansion uses a process in
precautions, see 8.1.1, 9.2, 10.1.2 and 10.2.5.
which the test gas is cooled rapidly to determine dew point
2. Referenced Documents temperature. This rapid exhausting of the test gas to atmo-
sphere results in an expansion and cooling of the gas. If the
2.1 ASTM Standards:
cooling is sufficient to reduce the temperature of the gas to or
D 1933 Specification for Nitrogen Gas as an Electrical
2 below the dew point, water vapor will condense out in the form
Insulating Material
of a fine mist or fog. Successive trials will determine the
D 2472 Specification for Sulfur Hexafluoride
minimum initial pressure that will produce a fog. From this, the
D 3283 Specification for Air as an Electrical Insulating
dew point temperature can be calculated.
Material
4.3.1 The relationship between pressure and temperature
3. Terminology
during adiabatic expansion is as follows:
@K21/K#
3.1 Definitions:
T 5 T P /P
@ #
F I F I
where:
1 K = ratio of specific heats for a given gas,
These test methods are under the jurisdiction of ASTM Committee D-27 on
T = final temperature,
Electrical Insulating Liquids and Gasesand are the direct responsibility of Subcom-
F
mittee D27.07on Physical Test.
T = initial temperature,
I
Current edition approved April 10, 1997. Published November 1997. Originally
P = final pressure, and
F
published as D 2029 – 64T. Last previous edition D 2029 – 92.
P = initial pressure.
2 I
Annual Book of ASTM Standards, Vol 10.03.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 2029 – 97
4.4 Method D—The capacitance method uses a moisture 6.3.3 For Methods A, B, C, and D, that the measuring
sensor, typically aluminum oxide or silicon oxide, which system (instrument and tubing) must not entrain moisture. If
changes its electrical output with the amount of water vapor to any moisture is entrained, several hours may be required for
which it is exposed. the gas being measured to come into equilibrium with the
measuring system.
6.3.4 For Methods B and C, the sensitivity of the human eye
5. Significance and Use
in determining exactly when the dew first forms.
5.1 Certain gases have excellent dielectric and electric arc
interruption characteristics which make their use in electrical
7. General Requirements
installations very desirable.
7.1 Methods A, B, and C—Any properly constructed dew
5.2 Water content, as the test parameter, is of great impor-
point apparatus may be used that provides a means to satisfy
tance in determining the dielectric effectiveness of the gas.
the following basic requirements:
Under certain conditions, water may condense and become a
7.1.1 Control the flow of gas entering and leaving the
conducting liquid resulting in a catastrophic dielectric break-
apparatus while the apparatus is at a temperature at least 2°C
down of the insulation. The water content of these insulating
(3.6°F) above the dew point of the gas.
gases as expressed by dew point is listed in Specifications
7.1.2 Control the cooling rate of a chamber in the apparatus
D 1933, D 2473, and D 3283.
through which the flowing gas passes to a temperature low
5.3 Once the dew point is determined, a conversion to
enough to cause water vapor to condense from the gas.
moisture content may be performed using Table 1. Once
7.1.3 Detect the deposition of dew on the cold portion of the
moisture content is known, the lowest temperature at which gas
apparatus and measure the temperature at which dew is
insulated equipment can be safely operated can usually be
formed.
determined by reviewing manufacturers’ specifications for the
7.1.4 Ensure that the test gas is at or near atmospheric
equipment.
pressure and is isolated from contamination from other gases.
5.4 The dew point of the test gas is independent of the gas
7.2 Method D—Any properly constructed capacitive type
temperature but does depend on its pressure. Many moisture
moisture sensor may be used that provides a means to satisfy
measurement test instruments are sensitive to pressure, and
the following basic requirements:
display moisture values at the instrument inlet pressure and not
7.2.1 Expose the sensor to a gas that is at a temperature at
necessarily at the pressure of the system being sampled. It is
least 10°C (18°F) above the dew point of the gas.
therefore important to account for this condition to avoid
7.2.2 Measure the partial vapor pressure of water in a gas by
serious measurement errors.
means of a capacitive type sensor.
7.3 These test methods provide for several techniques, each
6. Interferences
utilizing different types of apparatus for measuring dew point.
6.1 Tubing:
The techniques in these test methods are provided for general
6.1.1 Most new metal tubing contains oil deposits on the
information and are not intended as a substitute for manufac-
interior walls due to the manufacturing process. This residue
turer’s instructions. When using any instrument, the manufac-
should be removed before using these lines for gas sampling.
turer’s instructions should be followed to ensure proper and
6.1.2 Tubing should be free of leaks, since even a pinhole
safe operation.
leak will result in a false indication (higher dew point), due to
the partial pressure of water vapor in the atmosphere. 8. Apparatus
6.1.3 When the gas being tested is extremely dry [dew point
8.1 General:
below approximately − 40°C (−40°F)], results can be mislead-
8.1.1 Tubing—Although not true of all applications, stain-
ing until the moisture adsorbed in the system (tubing, regula-
less steel, glass, and nickel alloy tubing are the best possible
tors, etc.) has been removed by purging with the test gas. At
nonhygroscopic materials and should be used for low dew
this point, all moisture present within the system should be due
point applications − 18 to − 73°C (0 to − 100°F). Copper and
to that contained in the test gas.
aluminum alloys, as well as stabilized polypropylene tubing,
6.2 When testing gases that contain readily liquefiable
are acceptable above − 29°C (−20°F) dew point.
impurities, it must be kept in mind that the dew point that is
NOTE 1—Warning: All materials will adsorb moisture to some extent;
measured by condensation type instruments may be due to
therefore, the internal surface of apparatus, tubing, and fittings should be
these impurities rather than to water. Under these conditions,
minimized to enable the system to dry out more quickly and achieve
the measured dew point is not an indication of the water
equilibrium sooner. However, it should be noted that when one switches
content of the gas.
from measurement of a high dew point to a lower dew point [that is, 0
6.3 Measurement of water vapor in very dry gases is to − 60°C (32 to − 76°F)] copper tubing might take1hor more to desorb
the moisture from the previous sample, whereas stainless steel will
complicated by four considerations, as follows:
equilibrate in approximately 10 min.
6.3.1 For Methods A, B, and C, the relatively large volume
of gas required to deposit sufficient water vapor to create the 8.1.2 Although not a requirement, the addition of a chart
“dew”. recorder to various automated systems makes determining
6.3.2 For Methods A, B, and C, that under very dry when the system has reached equilibrium much easier.
condition, the possibility exists to condense the test gas prior to 8.2 Method A—The automated chilled mirror dew point
deposition of moisture on the mirror. apparatus shown in Fig. 1 fulfills the requirements of 7.1. The
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 2029 – 97
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 volume lb/1000 volume
°C °F mg/L °C °F mg/L
3 3
ft percent ft percent
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 b
...