1、Designation: D 6097 01aAn 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 indicates the year oforigin
2、al 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 the relative resistance to ventedwater-t
3、ree growth in solid translucent thermoplastic or cross-linked electrical insulating materials. This test method isespecially applicable to extruded polymeric insulation materi-als used in medium-voltage cables.1.2 The values given in SI units are to be regarded as thestandard.1.3 This standard does
4、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 limitation prior to use. For specific hazardstatements see 8.1.
5、1.4 There is no similar or equivalent IEC standard.2. Referenced Documents2.1 ASTM Standards:D 1898 Practice for Sampling of Plastics2D 1928 Practice for Preparation of Compression-MoldedPolyethylene Test Sheets and Test Specimens3D 2275 Test Method for Voltage Endurance of Solid Elec-trical Insulat
6、ing Materials Subjected to Partial Discharges(Corona) on the Surface4D 3756 Test Method for Evaluation of Resistance to Elec-trical Breakdown by Treeing in Solid Dielectric MaterialsUsing Diverging Fields53. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 water tree length (WTL),
7、 nthe maximum length of astained tree-like micro-channel path in millimetres, measuredfrom 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
8、), nthe ver-tical distance in millimetres from the tip of the conical defectto the 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 2
9、3 6 2C in an aqueous conductivesolution of 1.0 N NaCl for 30 days. This controlled 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 e
10、nhancement equation.6This en-hanced electrical stress initiates the formation of a 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 a
11、s the resistance to water-treegrowth.5. Significance and Use5.1 This is a laboratory 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 electr
12、ical field.Water-treeing is the phenomenon which describes the appear-ance of tree-like growth in organic dielectrics under an ac fieldwhen exposed to moist environments. Two types of water-treesare formed. Bow tie trees (within the dielectric) and ventedwater-trees formed from conductive/insulating
13、 material inter-face into the insulating material. The water-trees referred to inthis test method are the vented 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 s
14、imulate the same inner and outer1This 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 Tests.Current edition approved Sept. 10, 2001. Published November 2001. Originallypu
15、blished as D 6097 97. Last previous edition D 6097 01.2Discontinued; see 1997 Annual Book of ASTM Standards, Vol 08.01.3Annual Book of ASTM Standards, Vol 08.01.4Annual Book of ASTM Standards, Vol 10.01.5Annual Book of ASTM Standards, Vol 10.02.6The sole source of supply of the base, Dow Corning 311
16、0RTV, the catalyst,Dow Corning RTV Catalyst S, and the sealant, Dow Corning Multipurpose SiliconeSealant 732, known to the committee at this time is Dow Corning, Inc., Midland, MI48686. If you are aware of alternative suppliers, please provide this information toASTM International Headquarters. Your
17、 comments will receive careful consider-ation at a meeting of the responsible technical committe, which you may attend.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.semiconductive shields saturated with moisture between theinsulati
18、on layer used in 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 insu
19、latingmaterials 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 l
20、ow resistance towater-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, aq
21、ueous so-lutions, 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 resu
22、lts.5.5 Tree-growth 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 oxid
23、izedproducts from 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
24、 growth. If there 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 st
25、ained for optical observation.Different materials may also have different temperatures andtimes to stain the oxidized (treed) regions due to their differentsoftening temperature.6. Apparatus6.1 Power Supply A high-voltage supply with a sinusoidalvoltage output of at least 5 kV at a frequency of 1 kH
26、z and anoutput power 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-la
27、yer metal mold. The top metal plate is flat. The centerplate 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 holes about 8 mm in diameter attwo cor
28、ners 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 holesFIG. 1 Test Specimen Mold CavityD 60972as the center plate. Each hole has the inside diameter of 4 mmto accommodate needles. The
29、 second 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 threa
30、ded 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 a
31、bove 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 ins
32、ide 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 diamet
33、er of 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
34、end, 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;
35、 provided 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 Microscop
36、eA microscope 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 abase6and a catalyst6.7.3 Multipurpose Silicone SealantOne-part silicone6rub-ber seala
37、nt.7.4 Staining Dye The staining dye is a mixture of themethylene blue and sodium hydroxide.7.5 Deionized Water, or distilled water.8. Hazards8.1 WarningLethal voltages are a potential hazard duringthe performance of this test method. It is essential that the testapparatus and all associated equipme
38、nt 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. ProvideFIG. 2 PMMA Specimen HolderD 60973means for use at the completion of any test to gr
39、ound 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 making h
40、igh-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 possibility
41、 of such occur-rences and to eliminate the possibility of personal injury. If thepotential for fire exists, have fire suppression equipmentavailable.NOTE 2WarningWater in the test tank is gradually evaporated.Keeping the water level constant is important to prevent an electricalhazard.9. Sampling9.1
42、 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 3.2mm w
43、ith 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 te
44、rephthalate 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 prev
45、ious 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, a
46、nd 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 a
47、t 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 other
48、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 spec
49、imensfrom 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 nitrogen instead of air. This step isnecessary to remove by-products of the peroxide decomposi-tion, some of which are known to be tree-retardants.10.5 Do not use test specimens that have visible bubbles orcracks. It is also desirable that the flat surfaces on both sides ofeach disk are smooth. A dummy or trial s
