1、Designation: D 2029 97 (Reapproved 2003)Standard Test Methods forWater Vapor Content of Electrical Insulating Gases byMeasurement of Dew Point1This standard is issued under the fixed designation D 2029; the number immediately following the designation indicates the year oforiginal adoption or, in th
2、e case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 Thes
3、e test methods describe the determination of thewater vapor content of electrical insulating gases by direct orindirect measurement of the dew point and the calculation ofthe water vapor content.1.2 The following four test methods are provided:1.2.1 Method A describes the automatic chilled mirrormet
4、hod for measurement of dew point as low as 73C(99F).1.2.2 Method B describes the manual chilled mirror or dewcup method for measurement of dew point as low as 73C(99F).1.2.3 Method C describes the adiabatic expansion methodfor measurement of dew point as low as 62C (80F).1.2.4 Method D describes the
5、 capacitance method for mea-surement of dew point as low as 110C (166F).1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine t
6、he applica-bility of regulatory limitations prior to use. For specificwarnings, see 8.1.1, 9.2, 10.1.2 and 10.2.5.2. Referenced Documents2.1 ASTM Standards:2D 1933 Specification for Nitrogen Gas as an ElectricalInsulating MaterialD 2472 Specification for Sulfur HexafluorideD 3283 Specification for A
7、ir as an Electrical InsulatingMaterial3. Terminology3.1 Definitions:3.1.1 dew point, nthe temperature to which a gas must becooled at constant pressure and constant water vapor content inorder for saturation to occur. Any further cooling usuallyresults in formation of the first drop of dew.3.1.2 hyg
8、roscopic, adjreadily taking up and retainingmoisture.4. Summary of Test Methods4.1 Method AThe automatic chilled mirror method usesthe chilled mirror dew point condensation principle to deter-mine the water vapor content in gas mixtures. An internalmirror, which is in the path of the test gas, is au
9、tomaticallycooled. Internal electronics sense the presence of moisture onthe mirror. The device then automatically brings itself toequilibrium and provides a direct reading of dew point tem-perature.4.2 Method BThis method uses the same basic condensa-tion principle in 4.1; however, the manual chill
10、ed mirrormethod uses a mixture of acetone and ice or other coolingmedia to manually chill the dew cup polished surface whichacts as the mirror.4.3 Method CAdiabatic expansion uses a process inwhich the test gas is cooled rapidly to determine dew pointtemperature. This rapid exhausting of the test ga
11、s to atmo-sphere results in an expansion and cooling of the gas. If thecooling is sufficient to reduce the temperature of the gas to orbelow the dew point, water vapor will condense out in the formof a fine mist or fog. Successive trials will determine theminimum initial pressure that will produce a
12、 fog. From this, thedew point temperature can be calculated.4.3.1 The relationship between pressure and temperatureduring adiabatic expansion is as follows:TF5 TIPF/PI#K21/K#where:K = ratio of specific heats for a given gas,TF= final temperature,TI= initial temperature,PF= final pressure, andPI= ini
13、tial pressure.1These test methods are under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and are the direct responsibility ofSubcommittee D27.07 on Physical Test.Current edition approved April 10, 1997. Published November 1997. Originallypublished as D 2029 64T. L
14、ast previous edition D 2029 92.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International,
15、 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.4 Method DThe capacitance method uses a moisturesensor, typically aluminum oxide or silicon oxide, whichchanges its electrical output with the amount of water vapor towhich it is exposed.5. Significance and Use5.1
16、 Certain gases have excellent dielectric and electric arcinterruption characteristics which make their use in electricalinstallations very desirable.5.2 Water content, as the test parameter, is of great impor-tance in determining the dielectric effectiveness of the gas.Under certain conditions, wate
17、r may condense and become aconducting liquid resulting in a catastrophic dielectric break-down of the insulation. The water content of these insulatinggases as expressed by dew point is listed in SpecificationsD 1933, D 2473, and D 3283.5.3 Once the dew point is determined, a conversion tomoisture c
18、ontent may be performed using Table 1. Oncemoisture content is known, the lowest temperature at which gasinsulated equipment can be safely operated can usually bedetermined by reviewing manufacturers specifications for theequipment.5.4 The dew point of the test gas is independent of the gastemperatu
19、re but does depend on its pressure. Many moisturemeasurement test instruments are sensitive to pressure, anddisplay moisture values at the instrument inlet pressure and notnecessarily at the pressure of the system being sampled. It istherefore important to account for this condition to avoidserious
20、measurement errors.6. Interferences6.1 Tubing:6.1.1 Most new metal tubing contains oil deposits on theinterior walls due to the manufacturing process. This residueshould be removed before using these lines for gas sampling.6.1.2 Tubing should be free of leaks, since even a pinholeleak will result in
21、 a false indication (higher dew point), due tothe partial pressure of water vapor in the atmosphere.6.1.3 When the gas being tested is extremely dry dew pointbelow approximately 40C (40F), results can be mislead-ing until the moisture adsorbed in the system (tubing, regula-tors, etc.) has been remov
22、ed by purging with the test gas. Atthis point, all moisture present within the system should be dueto that contained in the test gas.6.2 When testing gases that contain readily liquefiableimpurities, it must be kept in mind that the dew point that ismeasured by condensation type instruments may be d
23、ue tothese impurities rather than to water. Under these conditions,the measured dew point is not an indication of the watercontent of the gas.6.3 Measurement of water vapor in very dry gases iscomplicated by four considerations, as follows:6.3.1 For Methods A, B, and C, the relatively large volumeof
24、 gas required to deposit sufficient water vapor to create the“dew”.6.3.2 For Methods A, B, and C, that under very drycondition, the possibility exists to condense the test gas prior todeposition of moisture on the mirror.6.3.3 For Methods A, B, C, and D, that the measuringsystem (instrument and tubi
25、ng) must not entrain moisture. Ifany moisture is entrained, several hours may be required forthe gas being measured to come into equilibrium with themeasuring system.6.3.4 For Methods B and C, the sensitivity of the human eyein determining exactly when the dew first forms.7. General Requirements7.1
26、Methods A, B, and CAny properly constructed dewpoint apparatus may be used that provides a means to satisfythe following basic requirements:7.1.1 Control the flow of gas entering and leaving theapparatus while the apparatus is at a temperature at least 2C(3.6F) above the dew point of the gas.7.1.2 C
27、ontrol the cooling rate of a chamber in the apparatusthrough which the flowing gas passes to a temperature lowenough to cause water vapor to condense from the gas.7.1.3 Detect the deposition of dew on the cold portion of theapparatus and measure the temperature at which dew isformed.7.1.4 Ensure tha
28、t the test gas is at or near atmosphericpressure and is isolated from contamination from other gases.7.2 Method DAny properly constructed capacitive typemoisture sensor may be used that provides a means to satisfythe following basic requirements:7.2.1 Expose the sensor to a gas that is at a temperat
29、ure atleast 10C (18F) above the dew point of the gas.7.2.2 Measure the partial vapor pressure of water in a gas bymeans of a capacitive type sensor.7.3 These test methods provide for several techniques, eachutilizing different types of apparatus for measuring dew point.The techniques in these test m
30、ethods are provided for generalinformation and are not intended as a substitute for manufac-turers instructions. When using any instrument, the manufac-turers instructions should be followed to ensure proper andsafe operation.8. Apparatus8.1 General:8.1.1 TubingAlthough not true of all applications,
31、 stain-less steel, glass, and nickel alloy tubing are the best possiblenonhygroscopic materials and should be used for low dewpoint applications 18 to 73C (0 to 100F). Copper andaluminum alloys, as well as stabilized polypropylene tubing,are acceptable above 29C (20F) dew point. (WarningAll material
32、s will adsorb moisture to some extent; therefore,the internal surface of apparatus, tubing, and fittings should beminimized to enable the system to dry out more quickly andachieve equilibrium sooner. However, it should be noted thatwhen one switches from measurement of a high dew point toa lower dew
33、 point that is, 0 to 60C (32 to 76F) coppertubing might take1hormore to desorb the moisture from theprevious sample, whereas stainless steel will equilibrate inapproximately 10 min.)8.1.2 Although not a requirement, the addition of a chartrecorder to various automated systems makes determiningwhen t
34、he system has reached equilibrium much easier.D 2029 97 (2003)2TABLE 1 Relationship Between Dew Point and Moisture Content of GasesNOTE 1With 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 amou
35、nt 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 ContentC Flb/1000ft3mg/LvolumeApercentC Flb/1000ft3mg/LvolumeApercent50 122.0 5.16 82.7 12.2 16 3.2 0.079 1.27 0.14949 120.2 4.92 78.9 11.6 17 1.4 0.072 1.16 0.13648
36、118.4 4.69 75.1 11.0 18 0.4 0.066 1.06 0.12347 116.6 4.48 71.9 10.5 19 2.2 0.060 0.965 0.11246 114.8 4.26 68.4 9.95 20 4.0 0.055 0.882 0.10245 113.0 4.06 65.0 9.45 21 5.8 0.050 0.809 0.09344 111.2 3.88 62.1 8.99 22 7.6 0.046 0.733 0.08443 109.4 3.69 59.1 8.52 23 9.4 0.042 0.666 0.07642 107.6 3.52 56
37、.4 8.10 24 11.2 0.038 0.608 0.06941 105.8 3.34 53.5 7.67 25 13.0 0.035 0.556 0.06340 104.0 3.18 50.9 7.27 26 14.8 0.031 0.506 0.05739 102.2 3.02 48.4 6.89 26 16.6 0.028 0.454 0.05738 100.4 2.87 46.0 6.54 28 18.4 0.025 0.411 0.04637 98.6 2.74 43.8 6.20 29 20.2 0.023 0.377 0.04236 96.8 2.60 41.6 5.87
38、30 22.0 0.021 0.343 0.03835 95.0 2.46 39.4 5.55 31 23.8 0.019 0.307 0.03434 93.2 2.34 37.4 5.25 32 25.6 0.017 0.273 0.03033 91.4 2.22 35.6 4.96 33 27.4 0.015 0.246 0.02732 89.6 2.11 33.8 4.70 34 29.2 0.014 0.229 0.02531 87.8 2.00 32.0 4.44 35 31.0 0.013 0.202 0.02230 86.0 1.89 30.3 4.19 36 32.8 0.01
39、2 0.185 0.02029 84.2 1.84 29.2 4.01 37 34.6 0.010 0.167 0.01828 82.4 1.69 27.1 3.7 38 36.4 0.0093 0.149 0.01627 80.6 1.60 25.7 3.52 39 38.2 0.0082 0.131 0.01426 78.8 1.52 24.4 3.33 40 40.0 0.0074 0.119 0.012725 77.0 1.44 23.0 3.12 41 41.8 0.0068 0.107 0.011324 75.2 1.35 21.7 2.94 42 43.6 0.0060 0.09
40、6 0.010223 73.4 1.28 20.6 2.78 43 45.4 0.0054 0.086 0.009022 71.6 1.21 19.4 2.61 44 47.2 0.0047 0.076 0.008021 69.8 1.14 18.3 2.46 45 49.0 0.0042 0.068 0.007120 68.0 1.08 17.3 2.31 46 50.8 0.0038 0.061 0.006319 66.2 1.02 16.3 2.17 47 52.6 0.0034 0.054 0.005618 64.4 0.961 15.4 2.04 48 54.4 0.0031 0.0
41、49 0.005017 62.6 0.899 14.4 1.91 49 56.2 0.0027 0.043 0.004416 60.8 0.855 13.7 1.80 50 58.0 0.0024 0.038 0.003915 59.0 0.799 12.8 1.68 51 59.8 0.0021 0.034 0.003414 57.2 0.749 12.0 1.57 52 61.6 0.0019 0.030 0.003013 55.4 0.706 11.3 1.48 53 63.4 0.0017 0.027 0.002712 53.6 0.668 10.7 1.39 54 65.2 0.00
42、14 0.023 0.002311 51.8 0.620 9.94 1.29 55 67.0 0.0013 0.021 0.002110 50.0 0.584 9.37 1.21 56 68.8 0.0011 0.018 0.00189 48.2 0.547 8.76 1.13 57 70.6 0.0010 0.016 0.00168 46.4 0.516 8.27 1.06 58 72.4 0.00087 0.014 0.00147 44.6 0.482 7.73 0.988 59 74.2 0.00075 0.012 0.00126 42.8 0.452 7.25 0.924 60 76.
43、0 0.00069 0.011 0.00115 41.0 0.424 6.79 0.861 61 77.8 0.00059 0.0095 0.000924 39.2 0.399 6.36 0.804 62 79.6 0.00052 0.0083 0.000803 37.4 0.370 5.94 0.748 63 81.4 0.00046 0.0073 0.000702 35.6 0.346 5.55 0.696 64 83.2 0.00040 0.0064 0.000611 33.8 0.323 5.18 0.649 65 85.0 0.00035 0.0056 0.000530 32.0 0
44、.302 4.84 0.602 66 86.8 0.00030 0.0048 0.000451 30.2 0.280 4.49 0.556 67 88.6 0.00027 0.0043 0.000402 28.4 0.258 4.14 0.511 68 90.4 0.00022 0.0036 0.000343 26.6 0.238 3.81 0.470 69 92.2 0.00019 0.0031 0.000294 24.8 0.220 3.52 0.431 70 94.0 0.00017 0.0027 0.000255 23.0 0.202 3.24 0.396 71 95.8 0.0001
45、5 0.0024 0.000226 21.2 0.186 2.98 0.364 72 97.6 0.00013 0.0021 0.000197 19.4 0.171 2.74 0.333 73 99.4 0.00011 0.0018 0.000168 17.6 0.158 2.53 0.306 74 101.2 0.00009 0.0015 0.000149 15.8 0.145 2.32 0.280 75 103.0 0.00008 0.0013 0.0001210 14.0 0.134 2.14 0.257 76 104.8 0.00007 0.0011 0.0001011 12.2 0.
46、122 1.96 0.235 77 106.6 0.00006 0.0010 0.0000912 10.4 0.113 1.81 0.215 78 108.4 0.00005 0.0008 0.0000713 8.6 0.103 1.65 0.196 79 110.2 0.00004 0.0007 0.0000614 6.8 0.095 1.52 0.179 80 112.0 0.00004 0.0006 0.0000515 5.0 0.086 1.38 0.163 81 113.8 0.00003 0.0005 0.00004AVapor pressures in atmospheres a
47、t various dew points can be obtained by dividing the values for “volume percent in this table by 100. Calculations for this table weremade 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 t
48、o 0C.The vapor pressure of ice was used from 0 to 81C.D 2029 97 (2003)38.2 Method AThe automated chilled mirror dew pointapparatus shown in Fig. 1 fulfills the requirements of 7.1. Theapparatus typically consists of a test chamber having thefollowing components:8.2.1 Thermoelectric Heat Pump, equipp
49、ed with a suitabletemperature sensor embedded within the mirror that forms thecondensation surface on the heat pump/mirror assembly.8.2.2 Condensate Detector, with a suitable light source andphoto detector bridge network.8.2.3 Internal Power Supplies and Amplifiers as necessaryto integrate above components into a system.8.2.4 Tubing for Test Gas, one end con
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