ASTM_D_6180_-_98.pdf

Designation:D 6180 98Standard Test Method forStability of Insulating Oils of Petroleum Origin UnderElectrical Discharge1This standard is issued under the fixed designation D 6180;the number immediately following the designation indicates the year oforiginal adoption or,in the 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.1.Scope1.1 This test method covers a laboratory technique thatmeasures the stability of new,used,or reclaimed insulatingoils,similar to those described in Specification D 3487 in thepresence of a controlled electric discharge.When subjected tothis type of discharge,insulating oils absorb energy andproduce gases as well as ionized molecules(charge carriers).The quantity of these decay products can be measured and canprovide an indication of the stability of oils under the condi-tions of this test.1.2 The gases are retained in the discharge cell and theirpressure measured.The charge carriers remain in the testspecimen.The change in the dissipation factor before and afterthe discharge is determined.1.3 The values stated in SI units are to be regarded as thestandard.The values stated in parentheses are for informationonly.1.4 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 the applica-bility of regulatory limitations prior to use.Specific cautionarystatements are given in 5.3 and 7.1.2.Referenced Documents2.1 ASTM Standards:D 923 Practice for Sampling Electrical Insulating Liquids2D 924 Test Method for Dissipation Factor(or Power Factor)and Relative Permittivity(Dielectric Constant)of Electri-cal Insulating Liquids2D 3487 Specification for Mineral Insulating Oil Used inElectrical Apparatus22.2IEEE Standard:41995 IEEE Standard Techniques for High-Voltage Test-ing33.Summary of Test Method3.1 A test specimen is introduced into a discharge cell anddegassed under vacuum at room temperature.An ac potentialof 10 kV is applied between a high voltage electrode and agrounded salt water electrode for 300 min.The gradual rise ofthe pressure inside the discharge cell is measured on anelectronic vacuum meter as a function of time.The dissipationfactor of the oil at 100C is determined before and after thestability test.4.Significance and Use4.1 During this test,insulating oil in an evacuated cell issubjected to a high voltage discharge between two electrodes.The discharge generates free electrons.These electrons collidewith the oil molecules causing many of them to becomeelectronically excited.Some of these molecules lose thisenergy as a quanta of light emitting fluorescent radiation.Someof the other excited molecules decompose into gases,ionizedmolecules and free radicals.These changes can provide anindication of the stability of oils under the conditions of thistest method.The measures of these changes are the increase ofthe pressure in the test cell and the increase in the dissipationfactor of the test specimen.4.2 During the test,the gas content increases in the cell andthe concentration of charge carriers increases in the oil.5.Apparatus5.1 Discharge Cell,4shown in Fig.1,includes an electronicvacuum meter.The cell must be made of quartz,be of sphericalshape,and have a 500 mL capacity.The electrode is sealed inthe cell as shown in Fig.1.The free electrons are generated bya cylindrical copper electrode 15 mm(0.6 in.)in diameter and10 mm(0.4in.)long,which is placed in the center of thedischarge cell.5.2 Glass Dish,approximately 150 mm(6 in.)in diameterand 100 mm(4 in.)deep for holding a salt-water groundelectrode.5.3 Test Chamber,with safety interlocked door,whichdeenergizes the test transformer when opened and large enough1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and is the direct responsibility of Subcom-mittee D27.05 on Electrical Test.Current edition approved Oct.10,1998.Published January 1999.Originallypublished as D 6180-97.Last previous edition D 6180-97.2Annual Book of ASTM Standards,Vol 10.03.3Available from the Institute of Electrical and Electronic Engineers,Inc.,P.O.Box 1331,Piscataway,NJ 08855.4A suitable discharge cell is obtainable from Insoil Canada Ltd.,231 HampshirePlace,N.W.,Calgary,AB Canada T3A 4Y7.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.to contain the desired number of cells with at least 100 mm(4in.)clearance between cells,sides,and top.5.4 Power Source Step-Up Transformer,60 Hz,200 VA,115 or 230 V to at least 10 kV.Design the transformer of sucha size that,with the test specimen in the circuit,the voltagewaveshape is approximately a sinusoid with both half cyclesalike,and it should have a ratio of peak-to-rms value equal tothe=2 6 5%.