1、Designation: D 831 94 (Reapproved 2004)Standard Test Method forGas Content of Cable and Capacitor Oils1This standard is issued under the fixed designation D 831; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the gascontent of electrical insulating oils of low and mediumviscosities in the
3、general range up to 190 cSt at 104F (40C),such as are used in capacitors and paper-insulated electriccables and cable systems of the oil-filled type. The determina-tion of gas content is desirable for any insulating oil havingthese properties and intended for use in a degassed state.NOTE 1For testin
4、g insulating oils with viscosities of 19 cSt at 40C orbelow, see Test Method D 2945.1.2 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
5、 determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 2945 Test Method for Gas Content of Insulating Oils23. Summary of Test Method3.1 This test method consists essentially of feeding the oilinto an evacuated chamber in such a manner that th
6、e oil isthoroughly exposed to the vacuum, allowing free escape of anydissolved gas. From the volume of oil admitted to the chamber,the temperature, the pressure produced, and volume occupiedby the released gas, the gas volume under standard conditionsof pressure and temperature may be calculated as
7、a percentageby volume of oil.4. Significance and Use4.1 The gas content of cable and capacitor oils is consideredto be important, since the evolution of gas in the form ofbubbles can have an adverse effect on the insulating propertiesof these fluids. It is customary to degas these oils prior to use,
8、and this test method provides a means of determining the gascontent before and after degassing.5. Apparatus (see Fig. 1)5.1 Degassing ChamberDegassing chamber, A, made ofheat-resistant glass3(with calibrated oil well at bottom), havinga fixed total space volume of about 175 to 300 mL. The oil wellsh
9、all have a maximum capacity of 50 mL and shall becalibrated in 0.2-mL divisions.5.2 StopcocksGlass stopcocks, B and C, which shall havelarge-diameter barrels and a mirror finish to ensure againstleakage. Use stopcock grease on all stopcocks and ground-glass joints.5.3 AtomizerGlass pipet, D, placed
10、to drop oil on the sideof the degassing chamber, or5.3.1 Fritted Disk (Alternative)Capacity 30 mm,medium-porosity.NOTE 2Some experience has shown improvement in the atomizationprocess, particularly for oils of medium viscosity above 95 cSt at 40C, ifa 30-mm medium-porosity fritted disk is substitute
11、d for the pipet.5.4 Pressure Gage Pressure gage, E, of modified McLeodtype. Include the volume of this gage in the over-all volume ofthe apparatus (Note 3). This is essential and must also includethe volume of the gage-connecting tubing.NOTE 3The volume of the gage may be obtained from the manufac-t
12、urer or measured.5.5 Oil Trap, F, having a capacity of 250 mL.5.6 Thermometer, T, room ambient.5.7 Cold Trap, J, employed to eliminate possible error dueto presence of condensable vapors.5.8 Oven, K, employed to enhance the atomization process.The oven shall enclose the degassing chamber, A, between
13、stopcocks B and C, and point L. Provide suitable means forreading, maintaining, and regulating temperature in a rangefrom 30 to 150C. Measure temperature by means of athermocouple fastened to the oil chamber at the 25-mL markand suitably shielded to eliminate radiation errors.6. Sampling6.1 When con
14、venient, connect the degassing chamber of themeasuring equipment directly to the container from which the1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and is the direct responsibility of Subcom-mittee D27.03 on Analytical Tests.Current ed
15、ition approved Oct. 1, 2004. Published December 2004. Originallyapproved in 1945. Last previous edition approved in 1994 as D 831 94 (1999)e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vol
16、ume information, refer to the standards Document Summary page onthe ASTM website.3Borosilicate glass has been found to be satisfactory for this purpose.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.oil is to be sampled. This is usu
17、ally not convenient and is oftenimpossible. The method of sampling described in 6.2 isrecommended as an alternative.6.2 Use the sample container as shown in Fig. 2, whichconsists of a stainless steel cylinder 214 in. (5.7 cm) in insidediameter and 912 in. (24 cm) in length, closed at the bottom.Anal
18、uminum piston, accurately machined for an easy sliding fit, isinserted in the bore of the cylinder. Two nipples, diametricallyopposite each other, are inserted at the extreme bottom of thecylinder. Each nipple has a screw plug at the end with a gasketfor sealing. Make all connections to the measurin
19、g equipmentfrom the sample container using glass or metal tubing. Connectbutted joints using short sections of heavy-walled rubbertubing. Coat the tubing thoroughly with suitable sealingcompound. Take all samples under slight oil pressure, with thefollowing sequence of operations: Remove plugs from
20、bothnipples. Push the piston to the extreme bottom of the cylinder.Hold the cylinder so that the nipples point in a verticaldirection. Using a rubber tube connection, force oil in throughthe nipple in the lowest position and flush a few millilitres outthe opposite nipple to remove any trapped air bu
21、bbles. Theninsert the plug in the outlet nipple and allow oil to push thepiston up to fill the cylinder. Hold the piston at the top of thecylinder with one hand and plug the inlet nipple. The alumi-num piston “floats” on the oil as the level varies due totemperature changes or removal of test specim
22、ens and preventscontamination by absorption and diffusion. Fit the pistonaccurately so it moves down freely with decreasing oil level toprevent voids forming under the piston which would allowrapid absorption of air by the top oil. Draw the test specimencontinuously from the cylinder, weight the pis
23、ton to ensuremaintenance of contact with the oil. Wide variations in theresult are possible in two test specimens from the same sourceunless the greatest care is taken in the sampling procedure.Thisphase of the test is so involved with the details of whatconstitutes correct practice that ability to
24、procure consistentrepresentative test specimens depends, to a great extent, onwide experience. The chief precaution to the procurement ofrepresentative test specimens involves a complete flushing ofall piping and hose between the sample container and samplesource, such as pothead, joint, cable, oil
25、reservoir, etc., imme-diately preceding collection of the sample. Eliminate all longsampling pipe lines. After taking the test specimen, ensure thatthe piston always remains in contact with the oil prior to andduring withdrawal of the test specimen.7. Calibration of Apparatus7.1 Calibration and cond
26、itioning of the apparatus are oftendone by the manufacturer. If this has not been done, or if acheck is desired, the following procedures may be used:7.1.1 Clean the glass assembly with a cleaning solution,wash with distilled water, and dry. Weigh the empty glassapparatus with a slight film of greas
27、e on the stopcocks. Recordthe weight in grams (or volume in millilitres) as W. Fill theglass apparatus between stopcocks B and C and point M withdistilled water and weigh. Record the weight in grams (orvolume in millilitres) as R. The volume represented by thedifference between W and R added to the
28、volume of thepressure gage (Note 4) is the volume, V, of the tester inmillilitres. The volume, Vd, of the degassing chamber enclosedby the oven and the volume, Vt, of the cold trap covered withcoolant may be determined similarly. Correction for tempera-ture of water may be made, but is an unnecessar
29、y refinement.7.1.2 Empty and thoroughly dry the glass apparatus in anoven. Grease the stopcocks and mount the apparatus on asuitable frame.7.1.3 An alternative method of calibration on the completedassembly to determine the volume, V, utilizes a gas buretFIG. 1 Apparatus for Determination of Gas Con
30、tent of Cable andCapacitor OilsFIG. 2 Apparatus for Sampling OilsD 831 94 (2004)2procedure.After evacuating the assembled apparatus, includingthe vacuum gage, to 0.1 mm Hg or less, a calibrated amount ofair at atmospheric pressure is allowed to expand into theevacuated apparatus and the resultant pr
31、essure recorded. Thetotal apparatus volume may then be simply calculated.8. Procedure8.1 Raise the temperature of the oven to the desired leveland make certain that it remains constant within 62C for atleast 30 min. The temperature of the cold trap will depend onthe coolant employed. (The temperatur
32、e of liquid air, or liquidnitrogen, is 195C and of carbon dioxide snow is 78C.)8.2 Evacuate the degassing chamber with stopcock B closedand stopcock C open.8.3 When the McLeod gage is reasonably constant and lessthan 0.1 mm Hg (absolute pressure), close stopcock C for about15 min to test for any lea
33、ks. No observable pressure changeshould occur in this time. (Let the vacuum pump run continu-ously to enhance the seal of stopcock C.)8.4 Flush oil slowly from the sample through stopcocks Band C so as to wash thoroughly the walls of the glass tubingand to remove any trapped air bubbles in the syste
34、m abovestopcock B. (About 50 mL of oil are commonly used for thisflushing.)8.5 Re-evacuate the degassing chamber, close stopcock C,read the McLeod gage and record as P1, then by carefulmanipulation of stopcock B feed oil from the sample containerinto the degassing chamber at a very slow rate so that
35、 the oilfalls in single drops from pipet D. This rate will generallyaverage 1 drop/s or less.Afritted disk, if employed, requires noregulation as it is self-monitoring. In the case of any significantpositive pressure, a suitable means of reducing the pressureshould be employed so as to allow the fri
36、tted disk to beself-monitoring. The oil should show no appreciable tendencyto bubble or foam after falling into the oil well at the bottom ofthe degassing chamber. If this occurs the rate of flow should bedecreased.8.6 When 50 mL of oil (Note 4) have been degassed, closestopcock B and read the press
37、ure, P2, on the McLeod gage.Record P2, room temperature, ta, oven temperature, td, and coldtrap temperature, tt.NOTE 4Smaller sample volumes than 50 mL may be desirable whenmeasuring insulating liquids having high gas content.8.7 Remove the sample container from the apparatus withstopcock B closed.
38、Discharge the sample from the oil well byopening stopcock C. Vent the apparatus to atmosphere bycareful manipulation of stopcock B.9. Calculation9.1 Calculate the gas content as follows:G 535.9V1FV 2 Vd2 Vt!P22 P1!273 1 ta1Vd2 V1!P22 VdP1273 1 td1VtP22 P1!273 1 ttGwhere:G = gas content (at 760 mm Hg
39、 and 0C) expressed as apercentage by volume of oil,V = known total fixed volume of apparatus, mL,V1= volume of oil, mL,Vt= volume of cold trap covered by coolant, mL,Vd= volume of degassing chamber enclosed by oven, mL,P1= initial pressure of gas in apparatus, mm Hg,P2= final pressure of gas in appa
40、ratus, mm Hg,ta= ambient temperature, C,td= temperature of degassing chamber A, C, andtt= temperature of cold trap J, C.NOTE 5The calculation may appear to be tedious, but when the fixedvolumes and temperatures are substituted in the equation, it will be foundthat it can be simplified considerably.
41、Simplification will also be aided ifP1can be made low enough to be negligible.10. Precision and Bias10.1 PrecisionThis test method has been found to bereproducible to 60.02 % gas content for gas contents on theorder of 0.10 % (Note 6); for samples of higher gas content theabsolute error will be some
42、what greater but the percentageerror somewhat less.NOTE 6Consider the case of an oil with 0.10 % gas. For normalprocedure, values of initial pressure and end point would be 0.100 and0.300 mm Hg, respectively. This pressure increase would be developed by50 mL of oil tested at 50C in an apparatus havi
43、ng a total fixed-spacevolume of approximately 225 mL, the components of which have thefollowing volumes and temperatures: degassing chamber, 125 mL and50C; cold trap, 25 mL and 195C; pressure gage, 75 mL and 27C. TheStokes gage (Model 276-AA) can be read to 60.005 mm below 0.100mm; 60.025 mm between
44、 0.100 and 0.700 mm; and 60.050 mmbetween 0.700 and 5.000 mm. Oil volume can be read to 60.05 mL.Assuming errors in pressure and volume readings adding to give maxi-mum deviation, the resultant error would be 60.02 % gas content.10.2 Bias:10.2.1 A statement on the bias of this test method cannot bem
45、ade because there is no material available having an acceptedreference value.10.2.2 The expected value of the gas content determined bythis test method is essentially the true gas content provided thatthere are no leaks in the apparatus, there is no water vaporpresent, and an adequate water trap is
46、used in series with thevacuum gage, and provided that the techniques for achievingmaximum evolution of gas from the sample are carefullyfollowed.11. Keywords11.1 cable oil; capacitor oil; electrical insulating oil; gascontent; oil-filled cableD 831 94 (2004)3ASTM International takes no position resp
47、ecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This s
48、tandard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM Interna
49、tional Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the ab
