1、Designation: D 6097 01a (Reapproved 2008)e1An American National StandardStandard Test Method forRelative Resistance to Vented Water-Tree Growth in SolidDielectric Insulating Materials1This standard is issued under the fixed designation D 6097; the number immediately following the designation indicat
2、es 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 () indicates an editorial change since the last revision or reapproval.e1NOTEThe units statement in subsection 1.2 was corrected
3、 and the warning in old Note 2 was moved into the text of 8.2editorially in July 2008.1. Scope1.1 This test method covers the relative resistance to ventedwater-tree growth in solid translucent thermoplastic or cross-linked electrical insulating materials. This test method isespecially applicable to
4、 extruded polymeric insulation materi-als used in medium-voltage cables.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use
5、. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitation prior to use. For specific hazardstatements see 8.1.1.4 There is no similar or equivalent IEC standard.2. Referenced Documents2.1 AST
6、M Standards:2D 1898 Practice for Sampling of Plastics3D 1928 Practice for Preparation of Compression-MoldedPolyethylene Test Sheets and Test Specimens3D 2275 Test Method for Voltage Endurance of Solid Elec-trical Insulating Materials Subjected to Partial Discharges(Corona) on the SurfaceD 3756 Test
7、Method for Evaluation of Resistance to Elec-trical Breakdown by Treeing in Solid Dielectric MaterialsUsing Diverging Fields3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 water tree length (WTL), nthe maximum length of astained tree-like micro-channel path in millimetres, meas
8、uredfrom the tip of the conical defect in the direction of the conicalaxis.3.1.2 resistance to water-tree growth (RWTG) a dimen-sionless value which is L divided by the WTL.3.1.3 thickness of point-to-plane specimen (L), nthe ver-tical distance in millimetres from the tip of the conical defectto the
9、 opposite surface of the solid dielectric material.4. Summary of Test Method4.1 Ten compression-molded disk specimens, each contain-ing a conical-shaped defect, are subjected to an applied voltageof 5 kV at 1 kHz and 23 6 2C in an aqueous conductivesolution of 1.0 N NaCl for 30 days. This controlled
10、 conicaldefect is created by a sharp needle with an included angle of60 and a tip radius of 3 m. The electrical stress at the defecttip is enhanced and can be estimated by the Masons Hyper-bolic point-to-plane stress enhancement equation.4This en-hanced electrical stress initiates the formation of a
11、 ventedwater-tree grown from the defect tip. Each treed specimen isstained and sliced. The water-tree length and point-to-planespecimen thickness measured under microscope are used tocalculate a ratio that is defined as the resistance to water-treegrowth.5. Significance and Use5.1 This is a laborato
12、ry test designed to simulate the growthof vented water-trees in the solid dielectric insulating materialinitiated by a sharp protrusion at the insulating and conductiveinterface under a wet environment in a high electrical field.Water-treeing is the phenomenon which describes the appear-ance of tree
13、-like growth in organic dielectrics under an ac fieldwhen exposed to moist environments. Two types of water-trees1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.12 on Electrical Tes
14、ts.Current edition approved May 1, 2008. Published July 2008. Originally approvedin 1997. Last previous edition approved in 2001 as D 6097 01a.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vo
15、lume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.4The sole source of supply of the base, Dow Corning 3110RTV, the catalyst,Dow Corning RTV Catalyst S, and the sealant, Dow Corning Multipurpose SiliconeSealant 732, known to the committee at this time is Dow
16、 Corning, Inc., Midland, MI48686. If you are aware of alternative suppliers, please provide this information toASTM International Headquarters. Your comments will receive careful consider-ation at a meeting of the responsible technical committe, which you may attend.1Copyright ASTM International, 10
17、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.are formed. Bow tie trees (within the dielectric) and ventedwater-trees formed from conductive/insulating material inter-face into the insulating material. The water-trees referred to inthis test method are the vented
18、type. The insulating material isthe solid dielectric organic material. The conductive material isthe salt solution. This salt solution is used on both sides of theinsulating material to simulate the same inner and outersemiconductive shields saturated with moisture between theinsulation layer used i
19、n a medium-voltage underground powercable.5.2 This test method provides comparative data. The degreeof correlation with the performance in service has not beenestablished.5.3 The standard test conditions are designed to grow asufficient water-tree length for most solid dielectric insulatingmaterials
20、 of interest before electrical breakdown occurs. Ma-terials with a very high resistance to water-tree growth mayrequire a longer time under test conditions (such as 180 days)or higher voltage (such as 10 or 15 kV) in order to differentiatetheir performance. For materials with a very low resistance t
21、owater-tree growth, electrical breakdown may occur during the30-day testing time. A shorter testing time (such as one or tendays) is recommended to prevent electrical breakdown duringtesting for those low water-tree resistant materials.5.4 Other voltages, frequencies, temperatures, aqueous so-lution
22、s, and defects can be used to evaluate specific materialsfor specific applications. Temperatures should not exceed thesoftening or melting point of the material or 10 to 15C belowthe boiling point of the salt solution. Any nonstandard condi-tions should be reported along with the results.5.5 Tree-gr
23、owth rates generally increase with the test fre-quency. An acceleration factor due to frequency is given by(f/60)kwhere f is the test frequency and k is between 0.6 and0.7. The test frequency of 1 kHz is selected to accelerate thewater-tree growth. However, the chemical nature of oxidizedproducts fr
24、om water-treeing may be different at differentfrequency ranges.5.6 Two assumptions for this test method are: (1) all testedmaterials grow trees in the same power law kinetic manner and(2) the time under test conditions of 30 days is long enough toestablish the difference in water-tree growth. If the
25、re is a doubt,at least three different testing times (such as 30, 90, and 180days) should be used to verify their comparative performanceand disclose their kinetic nature of water-tree growth. Ofcourse, it is also assumed that all water-treed regions areoxidized regions that can be stained for optic
26、al observation.Different materials may also have different temperatures andtimes to stain the oxidized (treed) regions due to their differentsoftening temperature.6. Apparatus6.1 Power SupplyAhigh-voltage supply with a sinusoidalvoltage output of at least 5 kV at a frequency of 1 kHz and anoutput po
27、wer of 3 kVA.6.2 Conical Needles Conical needles are made from steelor tungsten carbide. Their dimensions are 14.5 6 0.5 mm long,4 6 0.2 mm in diameter, point radius of 3 6 1 m for theneedle tip radius, and 60 6 1 point angle.6.3 Test Specimen MoldThe test specimen mold is athree-layer metal mold. T
28、he top metal plate is flat. The centerFIG. 1 Test Specimen Mold CavityD 6097 01a (2008)e12plate has at least ten holes to make ten test specimens for eachmaterial. Each hole has a 25.4-mm diameter and at least31.75-mm spacing from center to center of each hole. Thecenter plate also has the guide hol
29、es about 8 mm in diameter attwo corners to mate with pins in the bottom plate section. Thebottom plate section consists of two metal plates boltedtogether. The first bottom plate has the same number of holesas the center plate. Each hole has the inside diameter of 4 mmto accommodate needles. The sec
30、ond bottom plate has theholes with an inside diameter of 10 mm. The center points ofall the holes in the bottom and center plates are matched andaligned. These holes at the second bottom plate are threaded toaccommodate the needle support member. The needle supportmember is fabricated from threaded
31、stainless steel rod drilled atone end to provide a snug fit for needles, and at the other endto accommodate an hexagonal head driver. Needles arethreaded into the support member. The needle and needlesupport assembly is carefully screwed into the base until theneedle point extends 3.2 6 0.1 mm above
32、 the surface. Fig. 1 isan example of the mold cavity.6.4 Specimen Holder The specimen holder, designed tohold at least ten specimens, is made from a solid block of clearpolymethyl methacrylate (PMMA). The PMMA is used be-cause of the ease of machining and its good electrical proper-ties. The inside
33、is machined to a depth of 50.8 mm with a12.7-mm wall thickness. The outside bottom has the samenumber of holes with an inside diameter of 25.4 mm with adepth of 6.35 mm, drilled with a spacing of 38.1 mm fromcenter to center of the holes. The inside bottom has the sameholes with an inside diameter o
34、f 12.7 mm and a depth of 6.35mm in line with the centers of the holes drilled at the outsidebottom. Fig. 2 is an example of the specimen holder.6.5 ElectrodesThe electrode is made from a 1-m length of24 AWG nickel-chromium wire or other suitable conductive,noncorrosive metal wire formed, on one end,
35、 into a closed loopabout 50 mm smaller in diameter than the inside diameter ofthe specimen holder with the remainder bent perpendicular tothe loop so that it can be connected to the transformer toconduct the voltage into the electrolyte (the salt solution).6.6 Water BathA circulating water bath; pro
36、vided withheaters and temperature controls if tests are to be made atelevated temperatures.NOTE 1Circulation of the solution in the bath even at room tempera-ture is necessary to remove gas bubbles formed at the interface of thesolution and the test specimens caused by electrolysis.6.7 MicroscopeA m
37、icroscope equipped for 20 and 1003magnification.7. Reagents7.1 SaltReagent-grade sodium chloride.7.2 SealantsThe material used for sealing in this testmethod is a two-part silicone rubber sealant consisting of abase4and a catalyst.47.3 Multipurpose Silicone SealantOne-part silicone4rub-ber sealant.7
38、.4 Staining Dye The staining dye is a mixture of themethylene blue and sodium hydroxide.7.5 Deionized Water, or distilled water.FIG. 2 PMMA Specimen HolderD 6097 01a (2008)e138. Hazards8.1 WarningLethal voltages are a potential hazard duringthe performance of this test method. It is essential that t
39、he testapparatus and all associated equipment that may be electricallyconnected to it be properly designed and installed for safeoperation.8.2 Solidly ground all electrically conductive parts that maybe possible for a person to contact during the test. Providemeans for use at the completion of any t
40、est to ground any partswhich were at high voltage during the test or have the potentialfor acquiring an induced charge during the test or retaining acharge even after disconnection of the voltage source. Thor-oughly instruct all operators as to the correct procedures forperforming tests safely. When
41、 making high-voltage tests,particularly in compressed gas, oil, water, or aqueous solution,it is possible for the energy released at breakdown to besufficient to result in fire, explosion, or rupture of the testchamber. Design test equipment, test chambers, and testspecimens so as to minimize the po
42、ssibility of such occur-rences and to eliminate the possibility of personal injury. If thepotential for fire exists, have fire suppression equipmentavailable.WarningWater in the test tank is gradually evaporated.Keeping the water level constant is important to prevent anelectrical hazard.9. Sampling
43、9.1 Sample in accordance with Practice D 1898.10. Test Specimen10.1 Geometry of Test SpecimensThe test specimen is adisk containing a conical defect at the center of one side. Thedisk has a diameter of 25.4 mm and a thickness of 6.35 mm.This conical defect has a diameter of 3.2 mm and height of 3.2m
44、m with an included angle of 60. The radius of the cone tipis 3 6 1 m. Fig. 3 is the geometry of the test specimen.10.2 Preparation of Test SpecimensCompression moldten specimens for each solid dielectric material using thepreparation method described in Practice D 1928. Use apre-drilled polyethylene
45、 terephthalate sheet over needles tocover the metal surface of the bottom section of the testspecimen mold to prevent cross contamination from theprevious material residue.Apply a colorless mold release agentto all surfaces of the center section of the mold, to preventcross contamination from the pr
46、evious material residue. Themold release agent should not contain grease, wax, or siliconeoil. Weigh a sufficient amount of each sample and fill the moldwith the material. Cover the material with a polyethyleneterephthalate sheet under the top test specimen mold plate. Putthe mold assembly together,
47、 and place the entire mold assem-bly in a hydraulic press and complete the molding cycle.10.3 Molding ConditionsFor thermoplastic polyethylene,the molding cycle is 5 min at a low pressure of 0.30 MPa, 2min at a high pressure of 3 MPa at 160 6 5C. For cross-linkedpolyethylene, the mold cycle is 5 min
48、 at 125 6 5C at a lowpressure of 0.30 MPa, 2 min at 120 6 5C at a high pressureof 3 MPa, and 15 min at 175 6 5C at the same high pressure.Cool the mold in the press at 15C/min to ambient temperature.See Practice D 1928. Different materials may have differentconditions for molding. For materials othe
49、r than polyethylene,obtain molding conditions from the material supplier.10.3.1 Remove the mold assembly from the press and takeoff the top plate. Slowly lift the center section of the mold,containing specimens, away from needles. Be careful not todrag material across needle tips. Remove the test specimensfrom the mold using a 25.4-mm diameter punch.10.4 Peroxide Cross-linked MaterialsHeat in a vacuumoven at a temperature of 80 6 3C and an absolute pressure of133 Pa (1 mm Hg) or less for 160 to 168 h. When releasing thevacuum do so with nitroge
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