ASTM D2029-97(2003)
(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
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 Adescribes the automatic chilled mirror method for measurement of dew point as low as -73°C (-99°F).
1.2.2 Method Bdescribes the manual chilled mirror or dew cup method for measurement of dew point as low as -73ˌC (-99°F).
1.2.3 Method Cdescribes the adiabatic expansion method for measurement of dew point as low as -62°C (-80°F).
1.2.4 Method Ddescribes the capacitance method for measurement of dew point as low as -110°C (-166°F).
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:D 2029–97 (Reapproved 2003)
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.Anumber 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—thetemperaturetowhichagasmustbe
cooledatconstantpressureandconstantwatervaporcontentin
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
warnings, 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
D1933 Specification for Nitrogen Gas as an Electrical
belowthedewpoint,watervaporwillcondenseoutintheform
Insulating Material
of a fine mist or fog. Successive trials will determine the
D2472 Specification for Sulfur Hexafluoride
minimuminitialpressurethatwillproduceafog.Fromthis,the
D3283 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:
These test methods are under the jurisdiction of ASTM Committee D27 on
K = ratio of specific heats for a given gas,
Electrical Insulating Liquids and Gases and are the direct responsibility of
T = final temperature,
F
Subcommittee D27.07 on Physical Test.
T = initial temperature,
Current edition approvedApril 10, 1997. Published November 1997. Originally
I
published as D2029–64T. Last previous edition D2029–92. P = final pressure, and
F
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
P = initial pressure.
I
contactASTM Customer Service at service@astm.org. ForAnnual Book ofASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 2029–97 (2003)
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.
5. Significance and Use 6.3.4 ForMethodsBandC,thesensitivityofthehumaneye
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.
5.2 Water content, as the test parameter, is of great impor- 7.1 Methods A, B, and C—Any properly constructed dew
tance in determining the dielectric effectiveness of the gas. point apparatus may be used that provides a means to satisfy
Under certain conditions, water may condense and become a the following basic requirements:
conducting liquid resulting in a catastrophic dielectric break- 7.1.1 Control the flow of gas entering and leaving the
down of the insulation. The water content of these insulating
apparatus while the apparatus is at a temperature at least 2°C
gases as expressed by dew point is listed in Specifications (3.6°F) above the dew point of the gas.
D1933, D2473, and D3283.
7.1.2 Control the cooling rate of a chamber in the apparatus
5.3 Once the dew point is determined, a conversion to through which the flowing gas passes to a temperature low
moisture content may be performed using Table 1. Once
enough to cause water vapor to condense from the gas.
moisturecontentisknown,thelowesttemperatureatwhichgas 7.1.3 Detectthedepositionofdewonthecoldportionofthe
insulated equipment can be safely operated can usually be
apparatus and measure the temperature at which dew is
determined by reviewing manufacturers’ specifications for the formed.
equipment.
7.1.4 Ensure that the test gas is at or near atmospheric
5.4 The dew point of the test gas is independent of the gas pressure and is isolated from contamination from other gases.
temperature but does depend on its pressure. Many moisture 7.2 Method D—Any properly constructed capacitive type
measurement test instruments are sensitive to pressure, and
moisture sensor may be used that provides a means to satisfy
displaymoisturevaluesattheinstrumentinletpressureandnot
the following basic requirements:
necessarily at the pressure of the system being sampled. It is
7.2.1 Expose the sensor to a gas that is at a temperature at
therefore important to account for this condition to avoid
least 10°C (18°F) above the dew point of the gas.
serious measurement errors.
7.2.2 Measurethepartialvaporpressureofwaterinagasby
means of a capacitive type sensor.
6. Interferences
7.3 These test methods provide for several techniques, each
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 Whenthegasbeingtestedisextremelydry[dewpoint
below approximately−40°C (−40°F)], results can be mislead-
8.1 General:
ing until the moisture adsorbed in the system (tubing, regula-
8.1.1 Tubing—Although not true of all applications, stain-
tors, etc.) has been removed by purging with the test gas. At
less steel, glass, and nickel alloy tubing are the best possible
thispoint,allmoisturepresentwithinthesystemshouldbedue
nonhygroscopic materials and should be used for low dew
to that contained in the test gas.
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
6.3.1 For MethodsA, B, and C, the relatively large volume tubing might take1hor more to desorb the moisture from the
of gas required to deposit sufficient water vapor to create the previous sample, whereas stainless steel will equilibrate in
“dew”. approximately 10 min.)
6.3.2 For Methods A, B, and C, that under very dry 8.1.2 Although not a requirement, the addition of a chart
condition,thepossibilityexiststocondensethetestgaspriorto recorder to various automated systems makes determining
deposition of moisture on the mirror. when the system has reached equilibrium much easier.
D 2029–97 (2003)
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 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.
D 2029–97 (2003)
8.2 Method A—The automated chilled mirror dew point
apparatus shown in Fig. 1 fulfills the requirements
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.