1、Designation:D 2298-81 4cTb AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race St.,Philadelphia,Pa.19103 Reprinted from the Annual Book of ASTM Standards,Copyright ASTM If not listed in the current combined index,will appear in the next edition.Standard Test Method for STABILITY OF INSULATING OILS
2、UNDER ELECTRICAL STRESS(MERRELL TEST)This standard is issued under the fixed designation D 2298 the number immediately foliowing the designation indicates the year of original adoption or,in the case of revision,lhe year of last revision.A number in parentheses indicates the year of last reapproval.
3、1.scope I.1 This method covers the determination of stability of electrical insulating oils,such as are used in cables and capacitors,by subjecting them to electric discharge under prescribed conditions for a fmed period of time and eval-uating the amount of gas evolved.2.Applicable Document 2.1 AST
4、M Standard D 923 Sampling Electrical Insulating Liq-uid?3.Summary of Methods 3.1 A sample of oil is admitted under vac-uum into the evacuated cell and,at room tem-perature,10 O00 V is applied between the high-voltage electrode and the grounded salt-water electrode for IO00 min.At the conclusion of t
5、he test,the manometer is read.The amount of gas evolved is a function of the pressure at-tained.The power factor of the oil at 100C,or other pertinent characteristics,may be deter-mined before and after the stability test.4.Significance 4.1 When subjected to load cycling,some types of oil-impregnate
6、d paper cable may de-velop partial vacuums or reduced pressure.The resistance of an oil to gas evolution or the change in other pertinent characteristics,such as the amount of power factor increase when the oil is exposed in a vacuum to electrical discharge,are criteria indicative of the suitabil-it
7、y of an oil for use in a cable.5.Apparatus 5.1 Discharge Cell,3 shown in Fig.1,includ-ing a closed-tube mercury manometer.5.2 Glass Dish,approximately 4 in.(100 mm)in diameter for holding salt-water ground elec-trode.5.3 Test Chamber,with safety interlocked door which de-energizes the test transform
8、er when opened and large enough to contain the desired number of cells with at least I-in.(25-mm)clearance between cells and sides,and top.5.4 Transformer,60-Hz,2OO-VA,115 or 230 V to at least 10 o00 V.The crest factor(ratio of maximum to mean effective)of the output voltage shall not differ from a
9、sine wave by more than 1 5%.5.5 Variable-Tap Autotransformer or Equiv-alent,500 VA min,115 or 230 V for applying voltage to transformer.5.6 Relay,115 or 230-V,double-pole,for energizing transformer.5.7 Switch,double-pole,115 or 230-V,on-off switch for applying voltage to circuit.5.8 Voltmeter-A volt
10、meter connected across the transformer primary may be used to determine voltage,provided it has been cali-brated in terms of the transformer high-voltage output when cells are under test.5.9 Vacuum Pump,laboratory-type capable of attaining a vacuum of less than 100 pm Hg.5.10 Clamp Stand,for support
11、ing cell in chamber.This method is under the jurisdiction of ASTM Com-mittee D-27 on Electrical Insulating Liquids and Gases.Current edition approved Feb.27,1981.Published April 198 I.Originally published as D 2298-64 T.Last pnvious edition D 2298-76.:Annuai Book of ASTM Siandards,Part 4 0.A suitabl
12、e discharge cell is obtainable from ibe Lapine Scientific Cq.375 Chestnut St.,Norwood,N.J.07648.1 NOTICE:This standard has either been superseded and replaced by a new version or discontinued.Contact ASTM International(www.astm.org)for the latest information.9 7007276 0025346 2b7 9 5.I I Vacuum Cage
13、,Stokes,or equivalent,to establish initial vacuum pressure.6.Sampling accordance with Method D 923.7.Cleaning Test Cell 7.1 Before using the cell,it should be thor-oughly flushed out with a suitable solvent such as trichloratrifluoroethane,petroleum ether,or pentane.Caution-Solvents should be used u
14、n-der a ventilated hood.Deposits that are not removed by solvent cleaning may accumulate on the sides of the flask.If this occurs,the inside of the flask should be purged with nitro-gen or oil-free air to remove any residual sol-vent vapors.The deposits may then be burned off with an oxygen gas flam
15、e applied to the outer glass surface at the location of the deposit.Usually it is not necessary to break the ground-glass joints except for the manometer connec-tion.8.Procedure 8.1 Test four cells at the same time,prepar-ing and connecting each in the same manner.8.2 Assemble the clean discharge ce
16、ll using a suitable silicone stopcock grease on all joints.Place the bottom of the cell in a water bath at 100OC(the salt-water dish containing fresh wa-ter on a hot plate is convenient).Use a clamp stand to support the cell at the lower ground-giass joint.Evacuate the cell for 1 h to an absolute pressure of 0.1 mm Hg or less.With the pump shut off for 15 min there should be no increase in the manometer reading;if there is,locate and stop the leak.8.3 Determine the power factor,or other desired