1、Designation: D2029 97 (Reapproved 2017)Standard Test Methods forWater Vapor Content of Electrical Insulating Gases byMeasurement of Dew Point1This standard is issued under the fixed designation D2029; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 Th
3、ese 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 mirrorm
4、ethod 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 t
5、he 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
6、 the 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:2D1933 Specification for Nitrogen Gas as an Electrical Insu-lating MaterialD2472 Specification for Sulfur HexafluorideD3283 Specification for
7、Air as an Electrical Insulating Ma-terial3. 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
8、hygroscopic, 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
9、 automaticallycooled. 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 ch
10、illed 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 in whichthe test gas is cooled rapidly to determine dew point tempera-ture. This rapid exhausting of the te
11、st gas to atmosphere resultsin an expansion and cooling of the gas. If the cooling issufficient to reduce the temperature of the gas to or below thedew point, water vapor will condense out in the form of a finemist or fog. Successive trials will determine the minimuminitial pressure that will produc
12、e a fog. From this, the dew pointtemperature 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,1These test methods are und
13、er the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gasesand are the direct responsibility of Subcom-mittee D27.07 on Physical Test.Current edition approved Jan. 1, 2017. Published February 2017. Originallyapproved in 1964. Last previous edition approved in 2008 as D2029 -
14、97 (2008).DOI: 10.1520/D2029-97R17.2For 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.Copyright ASTM Internation
15、al, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides
16、 and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.145 PF= final pressure, andPI= initial pressure.4.4 Method DThe capacitance method uses a moisturesensor, typically aluminum oxide or silicon oxide, whichchanges its electrical output with the amo
17、unt of water vapor towhich it is exposed.5. Significance and Use5.1 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
18、 dielectric effectiveness of the gas.Under certain conditions, water 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 SpecificationsD1933, D2472, and D3283
19、.5.3 Once the dew point is determined, a conversion tomoisture content 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
20、The dew point of the test gas is independent of the gastemperature 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 isth
21、erefore important to account for this condition to avoidserious 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
22、should be free of leaks, since even a pinholeleak will result in 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 a
23、dsorbed in the system (tubing,regulators, etc.) has been removed by purging with the test gas.At this point, all moisture present within the system should bedue to that contained in the test gas.6.2 When testing gases that contain readily liquefiableimpurities, it must be kept in mind that the dew p
24、oint that ismeasured by condensation type instruments may be due 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 follow
25、s:6.3.1 For Methods A, B, and C, the relatively large volumeof 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
26、 A, B, C, and D, that the measuringsystem (instrument and tubing) 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 determinin
27、g exactly when the dew first forms.7. General Requirements7.1 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 temper
28、ature at least 2C(3.6F) above the dew point of the gas.7.1.2 Control 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
29、measure the temperature at which dew isformed.7.1.4 Ensure that 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 requi
30、rements:7.2.1 Expose the sensor to a gas that is at a temperature 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 ap
31、paratus for measuring dew point.The techniques in these test methods 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. Apparatus
32、8.1 General:8.1.1 TubingAlthough not true of all applications, 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,
33、are acceptable above 29C (20F) dew point. (WarningAll materials 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 o
34、ne switches from measurement of a high dew point toa lower dew point that is, 0 to 60C (32 to 76F) copperD2029 97 (2017)245 TABLE 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
35、 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 ContentC Flb/1000ft3mg/LvolumeApercentC Flb/1000ft3mg/LvolumeApercent50 122.0 5.16 82.7 12.2 16 3.2 0.079
36、 1.27 0.14949 120.2 4.92 78.9 11.6 17 1.4 0.072 1.16 0.13648 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
37、109.4 3.69 59.1 8.52 23 9.4 0.042 0.666 0.07642 107.6 3.52 56.4 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.
38、74 43.8 6.20 29 20.2 0.023 0.377 0.04236 96.8 2.60 41.6 5.87 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
39、 35 31.0 0.013 0.202 0.02230 86.0 1.89 30.3 4.19 36 32.8 0.012 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
40、0.0068 0.107 0.011324 75.2 1.35 21.7 2.94 42 43.6 0.0060 0.096 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
41、0.0034 0.054 0.005618 64.4 0.961 15.4 2.04 48 54.4 0.0031 0.049 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
42、 63.4 0.0017 0.027 0.002712 53.6 0.668 10.7 1.39 54 65.2 0.0014 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 0.9
43、88 59 74.2 0.00075 0.012 0.00126 42.8 0.452 7.25 0.924 60 76.0 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
44、 33.8 0.323 5.18 0.649 65 85.0 0.00035 0.0056 0.000530 32.0 0.302 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
45、 0.00017 0.0027 0.000255 23.0 0.202 3.24 0.396 71 95.8 0.00015 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
46、.0 0.134 2.14 0.257 76 104.8 0.00007 0.0011 0.0001011 12.2 0.122 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
47、113.8 0.00003 0.0005 0.00004AVapor 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 weremade by using the International Critical Table values for the vapor pressure of ice and liquid water. The
48、 vapor pressure of liquid water was used for values from 50 to 0C.The vapor pressure of ice was used from 0 to 81C.D2029 97 (2017)345 tubing might take1hormore to desorb the moisture from theprevious sample, whereas stainless steel will equilibrate inapproximately 10 min.)8.1.2 Although not a requir
49、ement, the addition of a chartrecorder to various automated systems makes determiningwhen the system has reached equilibrium much easier.8.2 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 H
