Standard Historical Last Updated: Jan 27, 2017
ASTM D2029-97(2008)

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
ft3
mg/LvolumeA
percent
°C °Flb/1000
ft3
mg/LvolumeA
percent
50 122.05.1682.712.216 3.20.0791.27 0.149
49 120.24.9278.911.6171.40.0721.16 0.136
48 118.44.6975.111.018 0.40.0661.06 0.123
47 116.64.4871.910.519 2.20.0600.965 0.112
46 114.84.2668.49.9520 4.00.0550.882 0.102
45113.04.06 65.09.45215.80.0500.8090.093
44111.23.88 62.18.99227.60.0460.7330.084
43109.43.69 59.18.52239.40.0420.6660.076
42107.63.52 56.48.102411.20.0380.6080.069
41105.83.34 53.57.672513.00.0350.5560.063
40104.03.18 50.97.272614.80.0310.5060.057
39102.23.02 48.46.892616.60.0280.4540.057
38100.42.87 46.06.542818.40.0250.4110.046
37 98.62.7443.86.2029 20.20.0230.377 0.042
36 96.82.6041.65.8730 22.00.0210.343 0.038
35 95.02.4639.45.5531 23.80.0190.307 0.034
34 93.22.3437.45.2532 25.60.0170.273 0.030
33 91.42.2235.64.9633 27.40.0150.246 0.027
32 89.62.1133.84.7034 29.20.0140.229 0.025
31 87.82.0032.04.4435 31.00.0130.202 0.022
30 86.01.8930.34.1936 32.80.0120.185 0.020
29 84.21.8429.24.0137 34.60.0100.167 0.018
28 82.41.6927.13.738 36.40.00930.149 0.016
27 80.61.6025.73.5239 38.20.00820.131 0.014
26 78.81.5224.43.3340 40.00.00740.119 0.0127
25 77.01.4423.03.1241 41.80.00680.107 0.0113
24 75.21.3521.72.9442 43.60.00600.096 0.0102
23 73.41.2820.62.7843 45.40.00540.086 0.0090
22 71.61.2119.42.6144 47.20.00470.076 0.0080
21 69.81.1418.32.4645 49.00.00420.068 0.0071
20 68.01.0817.32.3146 50.80.00380.061 0.0063
19 66.21.0216.32.1747 52.60.00340.054 0.0056
18 64.40.96115.42.0448 54.40.00310.049 0.0050
17 62.60.89914.41.9149 56.20.00270.043 0.0044
16 60.80.85513.71.8050 58.00.00240.038 0.0039
15 59.00.79912.81.6851 59.80.00210.034 0.0034
14 57.20.74912.01.5752 61.60.00190.030 0.0030
13 55.40.70611.31.4853 63.40.00170.027 0.0027
12 53.60.66810.71.3954 65.20.00140.023 0.0023
11 51.80.6209.941.295567.0 0.00130.0210.0021
10 50.00.5849.371.215668.8 0.00110.0180.0018
948.20.5478.76 1.135770.60.00100.0160.0016
846.40.5168.27 1.065872.40.000870.0140.0014
744.60.4827.73 0.9885974.20.000750.0120.0012
642.80.4527.25 0.9246076.00.000690.0110.0011
541.00.4246.79 0.8616177.80.000590.00950.00092
439.20.3996.36 0.8046279.60.000520.00830.00080
337.40.3705.94 0.7486381.40.000460.00730.00070
235.60.3465.55 0.6966483.20.000400.00640.00061
133.80.3235.18 0.6496585.00.000350.00560.00053
032.00.3024.84 0.6026686.80.000300.00480.00045
130.2 0.2804.490.5566788.60.00027 0.00430.00040
228.4 0.2584.140.5116890.40.00022 0.00360.00034
326.6 0.2383.810.4706992.20.00019 0.00310.00029
424.8 0.2203.520.4317094.00.00017 0.00270.00025
523.0 0.2023.240.3967195.80.00015 0.00240.00022
621.2 0.1862.980.3647297.60.00013 0.00210.00019
719.4 0.1712.740.3337399.40.00011 0.00180.00016
817.60.1582.530.30674101.20.000090.00150.00014
915.80.1452.320.28075103.00.000080.00130.00012
1014.00.1342.140.25776104.80.000070.00110.00010
1112.20.1221.960.23577106.60.000060.00100.00009
1210.40.1131.810.21578108.40.000050.00080.00007
138.60.1031.650.19679110.20.000040.00070.00006
146.80.0951.520.17980112.00.000040.00060.00005
155.00.0861.380.16381113.80.000030.00050.00004

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.

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.

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Details
Book of Standards Volume: 10.03
Developed by Subcommittee: D27.07
Pages: 6
DOI: 10.1520/D2029-97R08
ICS Code: 29.040.20