Значение и использование

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/Lvolume^A
percent°C °Flb/1000
ft³mg/Lvolume^A
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 62.18.99−22−7.60.0460.7330.084 43109.43.69 59.18.52−23−9.40.0420.6660.076 42107.63.52 56.48.10–24−11.20.0380.6080.069 41105.83.34 53.57.67−25−13.00.0350.5560.063 40104.03.18 50.97.27−26−14.80.0310.5060.057 39102.23.02 48.46.89−26−16.60.0280.4540.057 38100.42.87 46.06.54−28−18.40.0250.4110.046 37 98.62.7443.86.20−29 −20.20.0230.377 0.042 36 96.82.6041.65.87−30 −22.00.0210.343 0.038 35 95.02.4639.45.55−31 −23.80.0190.307 0.034 34 93.22.3437.45.25−32 −25.60.0170.273 0.030 33 91.42.2235.64.96−33 −27.40.0150.246 0.027 32 89.62.1133.84.70−34 −29.20.0140.229 0.025 31 87.82.0032.04.44−35 −31.00.0130.202 0.022 30 86.01.8930.34.19−36 −32.80.0120.185 0.020 29 84.21.8429.24.01−37 −34.60.0100.167 0.018 28 82.41.6927.13.7−38 −36.40.00930.149 0.016 27 80.61.6025.73.52−39 −38.20.00820.131 0.014 26 78.81.5224.43.33−40 −40.00.00740.119 0.0127 25 77.01.4423.03.12−41 −41.80.00680.107 0.0113 24 75.21.3521.72.94−42 −43.60.00600.096 0.0102 23 73.41.2820.62.78−43 −45.40.00540.086 0.0090 22 71.61.2119.42.61−44 −47.20.00470.076 0.0080 21 69.81.1418.32.46−45 −49.00.00420.068 0.0071 20 68.01.0817.32.31−46 −50.80.00380.061 0.0063 19 66.21.0216.32.17−47 −52.60.00340.054 0.0056 18 64.40.96115.42.04−48 −54.40.00310.049 0.0050 17 62.60.89914.41.91−49 −56.20.00270.043 0.0044 16 60.80.85513.71.80−50 −58.00.00240.038 0.0039 15 59.00.79912.81.68−51 −59.80.00210.034 0.0034 14 57.20.74912.01.57−52 −61.60.00190.030 0.0030 13 55.40.70611.31.48−53 −63.40.00170.027 0.0027 12 53.60.66810.71.39−54 −65.20.00140.023 0.0023 11 51.80.6209.941.29−55−67.0 0.00130.0210.0021 10 50.00.5849.371.21−56−68.8 0.00110.0180.0018 948.20.5478.76 1.13−57−70.60.00100.0160.0016 846.40.5168.27 1.06−58−72.40.000870.0140.0014 744.60.4827.73 0.988−59−74.20.000750.0120.0012 642.80.4527.25 0.924−60−76.00.000690.0110.0011 541.00.4246.79 0.861−61−77.80.000590.00950.00092 439.20.3996.36 0.804−62−79.60.000520.00830.00080 337.40.3705.94 0.748−63−81.40.000460.00730.00070 235.60.3465.55 0.696−64−83.20.000400.00640.00061 133.80.3235.18 0.649−65−85.00.000350.00560.00053 032.00.3024.84 0.602−66−86.80.000300.00480.00045 −130.2 0.2804.490.556−67−88.60.00027 0.00430.00040 −228.4 0.2584.140.511−68−90.40.00022 0.00360.00034 −326.6 0.2383.810.470−69−92.20.00019 0.00310.00029 −424.8 0.2203.520.431−70−94.00.00017 0.00270.00025 −523.0 0.2023.240.396−71−95.80.00015 0.00240.00022 −621.2 0.1862.980.364−72−97.60.00013 0.00210.00019 −719.4 0.1712.740.333−73−99.40.00011 0.00180.00016 −817.60.1582.530.306−74−101.20.000090.00150.00014 −915.80.1452.320.280−75−103.00.000080.00130.00012 −1014.00.1342.140.257−76−104.80.000070.00110.00010 −1112.20.1221.960.235−77−106.60.000060.00100.00009 −1210.40.1131.810.215−78−108.40.000050.00080.00007 −138.60.1031.650.196−79−110.20.000040.00070.00006 −146.80.0951.520.179−80−112.00.000040.00060.00005 −155.00.0861.380.163−81−113.80.000030.00050.00004

^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.

Область применения

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.