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 β 73Β°C (β99Β°F).
1.2.2 Method B describes the manual chilled mirror or dew cup method for measurement of dew point as low as β 73Β°C (β99Β°F).
1.2.3 Method C describes the adiabatic expansion method for measurement of dew point as low as β 62Β°C (β80Β°F).
1.2.4 Method D describes the capacitance method for measurement of dew point as low as β 110Β°C (β166Β°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.
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
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
NoteβWith 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 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Β°C | Β°F | lb/1000 ft3 | mg/L | volumeA percent | Β°C | Β°F | lb/1000 ft3 | mg/L | volumeA percent |
| 50 | 122.0 | 5.16 | 82.7 | 12.2 | β16 | 3.2 | 0.079 | 1.27 | 0.149 |
| 49 | 120.2 | 4.92 | 78.9 | 11.6 | β17 | 1.4 | 0.072 | 1.16 | 0.136 |
| 48 | 118.4 | 4.69 | 75.1 | 11.0 | β18 | β0.4 | 0.066 | 1.06 | 0.123 |
| 47 | 116.6 | 4.48 | 71.9 | 10.5 | β19 | β2.2 | 0.060 | 0.965 | 0.112 |
| 46 | 114.8 | 4.26 | 68.4 | 9.95 | β20 | β4.0 | 0.055 | 0.882 | 0.102 |
| 45 | 113.0 | 4.06 | 65.0 | 9.45 | β21 | β5.8 | 0.050 | 0.809 | 0.093 |
| 44 | 111.2 | 3.88 | 62.1 | 8.99 | β22 | β7.6 | 0.046 | 0.733 | 0.084 |
| 43 | 109.4 | 3.69 | 59.1 | 8.52 | β23 | β9.4 | 0.042 | 0.666 | 0.076 |
| 42 | 107.6 | 3.52 | 56.4 | 8.10 | β24 | β11.2 | 0.038 | 0.608 | 0.069 |
| 41 | 105.8 | 3.34 | 53.5 | 7.67 | β25 | β13.0 | 0.035 | 0.556 | 0.063 |
| 40 | 104.0 | 3.18 | 50.9 | 7.27 | β26 | β14.8 | 0.031 | 0.506 | 0.057 |
| 39 | 102.2 | 3.02 | 48.4 | 6.89 | β26 | β16.6 | 0.028 | 0.454 | 0.057 |
| 38 | 100.4 | 2.87 | 46.0 | 6.54 | β28 | β18.4 | 0.025 | 0.411 | 0.046 |
| 37 | 98.6 | 2.74 | 43.8 | 6.20 | β29 | β20.2 | 0.023 | 0.377 | 0.042 |
| 36 | 96.8 | 2.60 | 41.6 | 5.87 | β30 | β22.0 | 0.021 | 0.343 | 0.038 |
| 35 | 95.0 | 2.46 | 39.4 | 5.55 | β31 | β23.8 | 0.019 | 0.307 | 0.034 |
| 34 | 93.2 | 2.34 | 37.4 | 5.25 | β32 | β25.6 | 0.017 | 0.273 | 0.030 |
| 33 | 91.4 | 2.22 | 35.6 | 4.96 | β33 | β27.4 | 0.015 | 0.246 | 0.027 |
| 32 | 89.6 | 2.11 | 33.8 | 4.70 | β34 | β29.2 | 0.014 | 0.229 | 0.025 |
| 31 | 87.8 | 2.00 | 32.0 | 4.44 | β35 | β31.0 | 0.013 | 0.202 | 0.022 |
| 30 | 86.0 | 1.89 | 30.3 | 4.19 | β36 | β32.8 | 0.012 | 0.185 | 0.020 |
| 29 | 84.2 | 1.84 | 29.2 | 4.01 | β37 | β34.6 | 0.010 | 0.167 | 0.018 |
| 28 | 82.4 | 1.69 | 27.1 | 3.7 | β38 | β36.4 | 0.0093 | 0.149 | 0.016 |
| 27 | 80.6 | 1.60 | 25.7 | 3.52 | β39 | β38.2 | 0.0082 | 0.131 | 0.014 |
| 26 | 78.8 | 1.52 | 24.4 | 3.33 | β40 | β40.0 | 0.0074 | 0.119 | 0.0127 |
| 25 | 77.0 | 1.44 | 23.0 | 3.12 | β41 | β41.8 | 0.0068 | 0.107 | 0.0113 |
| 24 | 75.2 | 1.35 | 21.7 | 2.94 | β42 | β43.6 | 0.0060 | 0.096 | 0.0102 |
| 23 | 73.4 | 1.28 | 20.6 | 2.78 | β43 | β45.4 | 0.0054 | 0.086 | 0.0090 |
| 22 | 71.6 | 1.21 | 19.4 | 2.61 | β44 | β47.2 | 0.0047 | 0.076 | 0.0080 |
| 21 | 69.8 | 1.14 | 18.3 | 2.46 | β45 | β49.0 | 0.0042 | 0.068 | 0.0071 |
| 20 | 68.0 | 1.08 | 17.3 | 2.31 | β46 | β50.8 | 0.0038 | 0.061 | 0.0063 |
| 19 | 66.2 | 1.02 | 16.3 | 2.17 | β47 | β52.6 | 0.0034 | 0.054 | 0.0056 |
| 18 | 64.4 | 0.961 | 15.4 | 2.04 | β48 | β54.4 | 0.0031 | 0.049 | 0.0050 |
| 17 | 62.6 | 0.899 | 14.4 | 1.91 | β49 | β56.2 | 0.0027 | 0.043 | 0.0044 |
| 16 | 60.8 | 0.855 | 13.7 | 1.80 | β50 | β58.0 | 0.0024 | 0.038 | 0.0039 |
| 15 | 59.0 | 0.799 | 12.8 | 1.68 | β51 | β59.8 | 0.0021 | 0.034 | 0.0034 |
| 14 | 57.2 | 0.749 | 12.0 | 1.57 | β52 | β61.6 | 0.0019 | 0.030 | 0.0030 |
| 13 | 55.4 | 0.706 | 11.3 | 1.48 | β53 | β63.4 | 0.0017 | 0.027 | 0.0027 |
| 12 | 53.6 | 0.668 | 10.7 | 1.39 | β54 | β65.2 | 0.0014 | 0.023 | 0.0023 |
| 11 | 51.8 | 0.620 | 9.94 | 1.29 | β55 | β67.0 | 0.0013 | 0.021 | 0.0021 |
| 10 | 50.0 | 0.584 | 9.37 | 1.21 | β56 | β68.8 | 0.0011 | 0.018 | 0.0018 |
| 9 | 48.2 | 0.547 | 8.76 | 1.13 | β57 | β70.6 | 0.0010 | 0.016 | 0.0016 |
| 8 | 46.4 | 0.516 | 8.27 | 1.06 | β58 | β72.4 | 0.00087 | 0.014 | 0.0014 |
| 7 | 44.6 | 0.482 | 7.73 | 0.988 | β59 | β74.2 | 0.00075 | 0.012 | 0.0012 |
| 6 | 42.8 | 0.452 | 7.25 | 0.924 | β60 | β76.0 | 0.00069 | 0.011 | 0.0011 |
| 5 | 41.0 | 0.424 | 6.79 | 0.861 | β61 | β77.8 | 0.00059 | 0.0095 | 0.00092 |
| 4 | 39.2 | 0.399 | 6.36 | 0.804 | β62 | β79.6 | 0.00052 | 0.0083 | 0.00080 |
| 3 | 37.4 | 0.370 | 5.94 | 0.748 | β63 | β81.4 | 0.00046 | 0.0073 | 0.00070 |
| 2 | 35.6 | 0.346 | 5.55 | 0.696 | β64 | β83.2 | 0.00040 | 0.0064 | 0.00061 |
| 1 | 33.8 | 0.323 | 5.18 | 0.649 | β65 | β85.0 | 0.00035 | 0.0056 | 0.00053 |
| 0 | 32.0 | 0.302 | 4.84 | 0.602 | β66 | β86.8 | 0.00030 | 0.0048 | 0.00045 |
| β1 | 30.2 | 0.280 | 4.49 | 0.556 | β67 | β88.6 | 0.00027 | 0.0043 | 0.00040 |
| β2 | 28.4 | 0.258 | 4.14 | 0.511 | β68 | β90.4 | 0.00022 | 0.0036 | 0.00034 |
| β3 | 26.6 | 0.238 | 3.81 | 0.470 | β69 | β92.2 | 0.00019 | 0.0031 | 0.00029 |
| β4 | 24.8 | 0.220 | 3.52 | 0.431 | β70 | β94.0 | 0.00017 | 0.0027 | 0.00025 |
| β5 | 23.0 | 0.202 | 3.24 | 0.396 | β71 | β95.8 | 0.00015 | 0.0024 | 0.00022 |
| β6 | 21.2 | 0.186 | 2.98 | 0.364 | β72 | β97.6 | 0.00013 | 0.0021 | 0.00019 |
| β7 | 19.4 | 0.171 | 2.74 | 0.333 | β73 | β99.4 | 0.00011 | 0.0018 | 0.00016 |
| β8 | 17.6 | 0.158 | 2.53 | 0.306 | β74 | β101.2 | 0.00009 | 0.0015 | 0.00014 |
| β9 | 15.8 | 0.145 | 2.32 | 0.280 | β75 | β103.0 | 0.00008 | 0.0013 | 0.00012 |
| β10 | 14.0 | 0.134 | 2.14 | 0.257 | β76 | β104.8 | 0.00007 | 0.0011 | 0.00010 |
| β11 | 12.2 | 0.122 | 1.96 | 0.235 | β77 | β106.6 | 0.00006 | 0.0010 | 0.00009 |
| β12 | 10.4 | 0.113 | 1.81 | 0.215 | β78 | β108.4 | 0.00005 | 0.0008 | 0.00007 |
| β13 | 8.6 | 0.103 | 1.65 | 0.196 | β79 | β110.2 | 0.00004 | 0.0007 | 0.00006 |
| β14 | 6.8 | 0.095 | 1.52 | 0.179 | β80 | β112.0 | 0.00004 | 0.0006 | 0.00005 |
| β15 | 5.0 | 0.086 | 1.38 | 0.163 | β81 | β113.8 | 0.00003 | 0.0005 | 0.00004 |
A Vapor pressures in atmospheres at various dew points can be obtained by dividing the values for βvolume 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 0Β°C. The vapor pressure of ice was used from 0 to β 81Β°C.
| SDO | ASTM: ASTM International |
| Document Number | D2029 |
| Publication Date | Dec. 1, 2008 |
| Language | en - English |
| Page Count | 6 |
| Revision Level | 97(2008) |
| Supercedes | |
| Committee | D27.07 |