1、Designation: D831 94 (Reapproved 2004) D831/D831M 12Standard Test Method forGas Content of Cable and Capacitor Oils1This standard is issued under the fixed designation D831;D831/D831M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision
2、, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the gas content of electrical insulating oils of low and me
3、dium viscosities inthe general range up to 190 cStmm2/s at 104F (40C),40C, such as are used in capacitors and paper-insulated electric cablesand cable systems of the oil-filled type. The determination of gas content is desirable for any insulating oil having these propertiesand intended for use in a
4、 degassed state.NOTE 1For testing insulating oils with viscosities of 19 cStmm2 at 40C or below,/s or below at 40C, see Test Method D2945.1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in eachsystem may not be exact equivalen
5、ts; therefore, each system shall be used independently of the other. Combining values from thetwo systems may result in non-conformance with the standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of
6、this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:D2945 Test Method for Gas Content of Insulating Oils2 (Withdrawn 2012)23. Summary of Test Method3.1 This test method cons
7、ists essentially of feeding the oil into an evacuated chamber in such a manner that the oil is thoroughlyexposed to the vacuum, allowing free escape of any dissolved gas. From the volume of oil admitted to the chamber, thetemperature, the pressure produced, and volume occupied by the released gas, t
8、he gas volume under standard conditions of pressureand temperature may be calculated as a percentage by volume of oil.4. Significance and Use4.1 The gas content of cable and capacitor oils is considered to be important, since the evolution of gas in the form of bubblescan have an adverse effect on t
9、he insulating properties of these fluids. It is customary to degas these oils prior to use, and this testmethod provides a means of determining the gas content before and after degassing.5. Apparatus (see Fig. 1)5.1 Degassing ChamberDegassing chamber, A, made of heat-resistant glass4 (with calibrate
10、d oil well at bottom), having afixed total space volume of about 175 to 300 mL. The oil well shall have a maximum capacity of 50 mL and shall be calibratedin 0.2-mL divisions.5.2 StopcocksGlass stopcocks, B and C, which shall have large-diameter barrels and a mirror finish to ensure against leakage.
11、Use stopcock grease5 on all stopcocks and ground-glass joints.5.3 AtomizerGlass pipet, D, placed to drop oil on the side of the degassing chamber, or5.3.1 Fritted Disk (Alternative)Capacity 30 mm, medium-porosity.NOTE 2Some experience has shown improvement in the atomization process, particularly fo
12、r oils of medium viscosity above 95 cStmm2/s at 40C,if a 30-mm medium-porosity fritted disk is substituted for the pipet.5.4 Pressure Gage Pressure gage, E, of modified McLeod type.6 Include the volume of this gage in the over-all volume ofthe apparatus (Note 3). This is essential and must also incl
13、ude the volume of the gage-connecting tubing.NOTE 3The volume of the gage may be obtained from the manufacturer or measured.5.5 Oil Trap, F, having a capacity of 250 mL.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.6 Thermometer,
14、T, room ambient.5.7 Cold Trap, J, employed to eliminate possible error due to presence of condensable vapors.5.8 Oven, K, employed to enhance the atomization process. The oven shall enclose the degassing chamber, A, betweenstopcocks B and C, and point L. Provide suitable means for reading, maintaini
15、ng, and regulating temperature in a range from 30to 150C. Measure temperature by means of a thermocouple fastened to the oil chamber at the 25-mL mark and suitably shieldedto eliminate radiation errors.6. Sampling6.1 When convenient, connect the degassing chamber of the measuring equipment directly
16、to the container from which the oilis to be sampled. This is usually not convenient and is often impossible. The method of sampling described in 6.2 is recommendedas an alternative.6.2 Use the sample container as shown in Fig. 2, which consists of a stainless steel cylinder 214 in. (5.7 cm)5.7 cm in
17、 insidediameter and 912 in. (24 cm)24 cm in length, closed at the bottom. An aluminum piston, accurately machined for an easy slidingfit, is inserted in the bore of the cylinder. Two nipples, diametrically opposite each other, are inserted at the extreme bottom of thecylinder. Each nipple has a scre
18、w plug at the end with a gasket for sealing. Make all connections to the measuring equipment fromthe sample container using glass or metal tubing. Connect butted joints using short sections of heavy-walled rubber tubing. Coatthe tubing thoroughly with suitable sealing compound. Take all samples unde
19、r slight oil pressure, with the following sequence ofoperations: Remove plugs from both nipples. Push the piston to the extreme bottom of the cylinder. Hold the cylinder so that thenipples point in a vertical direction. Using a rubber tube connection, force oil in through the nipple in the lowest po
20、sition and flush1 This test method is under the jurisdiction of ASTM Committee D27 on Electrical Insulating Liquids and Gasesand is the direct responsibility of Subcommittee D27.03on Analytical Tests.Current edition approved Oct. 1, 2004Nov. 1, 2012. Published December 2004November 2012. Originally
21、approved in 1945. Last previous edition approved in 1994 asD831 94 (1999)(2004).1. DOI: 10.1520/D0831-94R04.10.1520/D0831_D0831M-12.2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume info
22、rmation, refer to the standards Document Summary page on the ASTM website.2 The last approved version of this historical standard is referenced on www.astm.org.4 Borosilicate glass has been found to be satisfactory for this purpose.5 A stopcock grease equivalent to No. 15521. A readily available vac
23、uum sealing compound. Dow Corning grease #1597418, has been found to be satisfactory for thisuse.6 A McLeod gauge Flosdorf modification, available from Sigma-Aldrich Company, has been found satisfactory for this purpose. The sole source of supply of the apparatusknown to the committee at this time i
24、s Sigma-Aldrich Company. If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters.Your comments will receive careful consideration at a meeting of the responsible technical committee,1 which you may attend.FIG. 1 Apparatus for Determination of Gas
25、 Content of Cable and Capacitor OilsD831/D831M 122a few millilitres out the opposite nipple to remove any trapped air bubbles. Then insert the plug in the outlet nipple and allow oilto push the piston up to fill the cylinder. Hold the piston at the top of the cylinder with one hand and plug the inle
26、t nipple. Thealuminum piston “floats” on the oil as the level varies due to temperature changes or removal of test specimens and preventscontamination by absorption and diffusion. Fit the piston accurately so it moves down freely with decreasing oil level to preventvoids forming under the piston whi
27、ch would allow rapid absorption of air by the top oil. Draw the test specimen continuously fromthe cylinder, weight the piston to ensure maintenance of contact with the oil. Wide variations in the result are possible in two testspecimens from the same source unless the greatest care is taken in the
28、sampling procedure. This phase of the test is so involvedwith the details of what constitutes correct practice that ability to procure consistent representative test specimens depends, to agreat extent, on wide experience. The chief precaution to the procurement of representative test specimens invo
29、lves a completeflushing of all piping and hose between the sample container and sample source, such as pothead, joint, cable, oil reservoir, etc.,immediately preceding collection of the sample. Eliminate all long sampling pipe lines. After taking the test specimen, ensure thatthe piston always remai
30、ns in contact with the oil prior to and during withdrawal of the test specimen.7. Calibration of Apparatus7.1 Calibration and conditioning of the apparatus are often done by the manufacturer. If this has not been done, or if a checkis desired, the following procedures may be used:7.1.1 Clean the gla
31、ss assembly with a cleaning solution, wash with distilled water, and dry. Weigh the empty glass apparatuswith a slight film of grease on the stopcocks. Record the weight in grams (or volume in millilitres) as W. Fill the glass apparatusbetween stopcocks B and C and point M with distilled water and w
32、eigh. Record the weight in grams (or volume in millilitres) asR. The volume represented by the difference between W and R added to the volume of the pressure gage (Note 4) is the volume,V, of the tester in millilitres. The volume, Vd, of the degassing chamber enclosed by the oven and the volume, Vt,
33、 of the cold trapcovered with coolant may be determined similarly. Correction for temperature of water may be made, but is an unnecessaryrefinement.7.1.2 Empty and thoroughly dry the glass apparatus in an oven. Grease the stopcocks and mount the apparatus on a suitableframe. When properly applied, t
34、he grease will coat the whole conical surface of all ground glass, with less than 5 % of said greaseextruding beyond the ground surface.7.1.3 An alternative method of calibration on the completed assembly to determine the volume, V, utilizes a gas buret procedure.After evacuating the assembled appar
35、atus, including the vacuum gage, to 0.1 mm Hg or less, a calibrated amount of air atatmospheric pressure is allowed to expand into the evacuated apparatus and the resultant pressure recorded. The total apparatusvolume may then be simply calculated.8. Procedure8.1 Raise the temperature of the oven to
36、 the desired level and make certain that it remains constant within 62C for at least30 min. The temperature of the cold trap will depend on the coolant employed. (The temperature of liquid air, or liquid nitrogen,is 195C and of carbon dioxide snow is 78C.)8.2 Evacuate the degassing chamber with stop
37、cock B closed and stopcock C open.FIG. 2 Apparatus for Sampling OilsD831/D831M 1238.3 When the McLeod gage is reasonably constant and less than 0.1 mm Hg (absolute pressure), close stopcock C for about 15min to test for any leaks. No observable pressure change should occur in this time. In this time
38、, if the pressure rises by more than5 % of its initial absolute value, search for sources of leakage. (Let the vacuum pump run continuously to enhance the seal ofstopcock C.)8.4 Flush oil slowly from the sample through stopcocks B and C so as to wash thoroughly the walls of the glass tubing and tore
39、move any trapped air bubbles in the system above stopcock B. (About 50 mL of oil are commonly used for this flushing.)8.5 Re-evacuate the degassing chamber, close stopcock C, read the McLeod gage and record as P1, then by careful manipulationof stopcock B feed oil from the sample container into the
40、degassing chamber at a very slow rate so that the oil falls in single dropsfrom pipet D. This rate will generally average 1 drop/s or less. A fritted disk, ifwhen employed, requires no regulation as it isself-monitoring. In the case of any significant positive pressure, a suitable means of reducing
41、the pressure should be employed soas to allow the fritted disk to be self-monitoring. The oil should show no appreciable tendency to bubble or foam after falling intothe oil well at the bottom of the degassing chamber. If this occurs When this is seen to occur, the rate of flow should be decreased.8
42、.6 When 50 mL of oil (Note 4) have been degassed, close stopcock B and read the pressure, P2, on the McLeod gage. RecordP2, room temperature, ta, oven temperature, td, and cold trap temperature, tt.NOTE 4SmallerUse sample volumes aliquots smaller than 50 mL may be desirable when measuring for insula
43、ting liquids having high gas content.8.7 Remove the sample container from the apparatus with stopcock B closed. Discharge the sample from the oil well by openingstopcock C. Vent the apparatus to atmosphere by careful manipulation of stopcock B.D831/D831M 1249. Calculation9.1 Calculate the gas conten
44、t as follows:G 5 35.9V1FV 2Vd 2Vt!P22P1!2731ta1Vd 2V 1!P22VdP12731td 1VtP22P1!2731tt GG 5 35.9V1FV 2Vd 2Vt!P22P1!2731ta1Vd 2V 1!P22VdP12731td 1VtP22P1!2731tt Gwhere:G = gas content (at 760 mm Hg and 0C) expressed as a percentage by volume of oil,V = known total fixed volume of apparatus, mL,V1 = vol
45、ume 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 apparatus, mm Hg,ta = ambient temperature, C,td = temperature of degassing chamber A, C, andtt = tempera
46、ture of cold trap J, C.NOTE 5The calculation may appear to be tedious, but when the fixed volumes and temperatures are substituted in the equation, it will be found thatit can be simplified considerably. Simplification will also be aided if P1 can be made low enough to be negligible.10. Precision an
47、d Bias10.1 PrecisionThis test method has been found to be reproducible to 60.02 % gas content for gas contents on the order of0.10 % (Note 6); for samples of higher gas content the absolute error will be somewhat greater but the percentage error somewhatless.NOTE 6Consider the case of an oil with 0.
48、10 % gas. For normal procedure, values of initial pressure and end point would be 0.100 and 0.300 mmHg, respectively. This pressure increase would be developed by 50 mL of oil tested at 50C in an apparatus having a total fixed-space volume ofapproximately 225 mL, the components of which have the fol
49、lowing volumes and temperatures: degassing chamber, 125 mL and 50C; cold trap, 25 mLand 195C; pressure gage, 75 mL and 27C. The Stokes gage (Model 276-AA) can be read to 60.005 mm below 0.100 mm; 60.025 mm between0.100 and 0.700 mm; and 60.050 mm between 0.700 and 5.000 mm. Oil volume can be read to 60.05 mL. Assuming errors in pressure and volumereadings adding to give maximum 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 be made because there
