ASTM D6097-01a(2008)e1
(Test Method)Standard Test Method for Relative Resistance to Vented Water-Tree Growth in Solid Dielectric Insulating Materials
Standard Test Method for Relative Resistance to Vented Water-Tree Growth in Solid Dielectric Insulating Materials
SIGNIFICANCE AND USE
This is a laboratory test designed to simulate the growth of vented water-trees in the solid dielectric insulating material initiated by a sharp protrusion at the insulating and conductive interface under a wet environment in a high electrical field. Water-treeing is the phenomenon which describes the appearance of tree-like growth in organic dielectrics under an ac field when exposed to moist environments. Two types of water-trees are formed. Bow tie trees (within the dielectric) and vented water-trees formed from conductive/insulating material interface into the insulating material. The water-trees referred to in this test method are the vented type. The insulating material is the solid dielectric organic material. The conductive material is the salt solution. This salt solution is used on both sides of the insulating material to simulate the same inner and outer semiconductive shields saturated with moisture between the insulation layer used in a medium-voltage underground power cable.
This test method provides comparative data. The degree of correlation with the performance in service has not been established.
The standard test conditions are designed to grow a sufficient water-tree length for most solid dielectric insulating materials of interest before electrical breakdown occurs. Materials with a very high resistance to water-tree growth may require a longer time under test conditions (such as 180 days) or higher voltage (such as 10 or 15 kV) in order to differentiate their performance. For materials with a very low resistance to water-tree growth, electrical breakdown may occur during the 30-day testing time. A shorter testing time (such as one or ten days) is recommended to prevent electrical breakdown during testing for those low water-tree resistant materials.
Other voltages, frequencies, temperatures, aqueous solutions, and defects can be used to evaluate specific materials for specific applications. Temperatures should not exceed the softening or ...
SCOPE
1.1 This test method covers the relative resistance to vented water-tree growth in solid translucent thermoplastic or cross-linked electrical insulating materials. This test method is especially applicable to extruded polymeric insulation materials used in medium-voltage cables.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitation prior to use. For specific hazard statements see 8.1.
1.4 There is no similar or equivalent IEC standard.
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´1
Designation: D6097 − 01a (Reapproved 2008)
Standard Test Method for
Relative Resistance to Vented Water-Tree Growth in Solid
Dielectric Insulating Materials
This standard is issued under the fixed designation D6097; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—The units statement in subsection 1.2 was corrected and the warning in old Note 2 was moved into the text of
8.2 editorially in July 2008.
1. Scope Using Diverging Fields
1.1 This test method covers the relative resistance to vented
3. Terminology
water-tree growth in solid translucent thermoplastic or cross-
3.1 Definitions of Terms Specific to This Standard:
linked electrical insulating materials. This test method is
3.1.1 water tree length (WTL), n—the maximum length of a
especially applicable to extruded polymeric insulation materi-
stained tree-like micro-channel path in millimetres, measured
als used in medium-voltage cables.
fromthetipoftheconicaldefectinthedirectionoftheconical
1.2 The values stated in SI units are to be regarded as
axis.
standard. No other units of measurement are included in this
3.1.2 resistance to water-tree growth (RWTG)— a dimen-
standard.
sionless value which is L divided by the WTL.
1.3 This standard does not purport to address all of the
3.1.3 thickness of point-to-plane specimen (L), n—the ver-
safety concerns, if any, associated with its use. It is the
tical distance in millimetres from the tip of the conical defect
responsibility of the user of this standard to establish appro-
to the opposite surface of the solid dielectric material.
priate safety and health practices and determine the applica-
bility of regulatory limitation prior to use. For specific hazard
4. Summary of Test Method
statements see 8.1.
4.1 Ten compression-molded disk specimens, each contain-
1.4 There is no similar or equivalent IEC standard.
ingaconical-shapeddefect,aresubjectedtoanappliedvoltage
2. Referenced Documents of 5 kV at 1 kHz and 23 6 2°C in an aqueous conductive
2 solution of 1.0 N NaCl for 30 days. This controlled conical
2.1 ASTM Standards:
defect is created by a sharp needle with an included angle of
D1898Practice for Sampling of Plastics (Withdrawn 1998)
60° and a tip radius of 3 µm. The electrical stress at the defect
D1928Practice for Preparation of Compression-Molded
tip is enhanced and can be estimated by the Mason’s Hyper-
PolyethyleneTest Sheets andTest Specimens (Withdrawn
3 bolic point-to-plane stress enhancement equation. This en-
2001)
hanced electrical stress initiates the formation of a vented
D2275Test Method for Voltage Endurance of Solid Electri-
water-tree grown from the defect tip. Each treed specimen is
cal Insulating Materials Subjected to Partial Discharges
stained and sliced. The water-tree length and point-to-plane
(Corona) on the Surface
specimen thickness measured under microscope are used to
D3756Test Method for Evaluation of Resistance to Electri-
calculate a ratio that is defined as the resistance to water-tree
cal Breakdown by Treeing in Solid Dielectric Materials
growth.
5. Significance and Use
This test method is under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and is the direct responsibility of
5.1 Thisisalaboratorytestdesignedtosimulatethegrowth
Subcommittee D09.12 on Electrical Tests.
of vented water-trees in the solid dielectric insulating material
CurrenteditionapprovedMay1,2008.PublishedJuly2008.Originallyapproved
in 1997. Last previous edition approved in 2001 as D6097–01a. DOI: 10.1520/
D6097-01AR08E01.
2 4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or The sole source of supply of the base, Dow Corning 3110RTV, the catalyst,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM DowCorningRTVCatalystS,andthesealant,DowCorningMultipurposeSilicone
Standards volume information, refer to the standard’s Document Summary page on Sealant732,knowntothecommitteeatthistimeisDowCorning,Inc.,Midland,MI
the ASTM website. 48686. If you are aware of alternative suppliers, please provide this information to
The last approved version of this historical standard is referenced on ASTM International Headquarters. Your comments will receive careful consider-
www.astm.org. ation at a meeting of the responsible technical committe, which you may attend.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6097 − 01a (2008)
initiated by a sharp protrusion at the insulating and conductive days) is recommended to prevent electrical breakdown during
interface under a wet environment in a high electrical field. testing for those low water-tree resistant materials.
Water-treeing is the phenomenon which describes the appear-
5.4 Other voltages, frequencies, temperatures, aqueous
anceoftree-likegrowthinorganicdielectricsunderanacfield
solutions,anddefectscanbeusedtoevaluatespecificmaterials
whenexposedtomoistenvironments.Twotypesofwater-trees
for specific applications. Temperatures should not exceed the
are formed. Bow tie trees (within the dielectric) and vented
softening or melting point of the material or 10 to 15°C below
water-trees formed from conductive/insulating material inter-
the boiling point of the salt solution. Any nonstandard condi-
face into the insulating material. The water-trees referred to in
tions should be reported along with the results.
this test method are the vented type. The insulating material is
thesoliddielectricorganicmaterial.Theconductivematerialis
5.5 Tree-growth rates generally increase with the test fre-
the salt solution. This salt solution is used on both sides of the
quency. An acceleration factor due to frequency is given by (
insulating material to simulate the same inner and outer
k
f/60) wherefisthetestfrequencyandkisbetween0.6and0.7.
semiconductive shields saturated with moisture between the
The test frequency of 1 kHz is selected to accelerate the
insulation layer used in a medium-voltage underground power
water-tree growth. However, the chemical nature of oxidized
cable.
products from water-treeing may be different at different
5.2 Thistestmethodprovidescomparativedata.Thedegree
frequency ranges.
of correlation with the performance in service has not been
established. 5.6 Two assumptions for this test method are: (1) all tested
materialsgrowtreesinthesamepowerlawkineticmannerand
5.3 The standard test conditions are designed to grow a
(2) the time under test conditions of 30 days is long enough to
sufficient water-tree length for most solid dielectric insulating
establishthedifferenceinwater-treegrowth.Ifthereisadoubt,
materials of interest before electrical breakdown occurs. Ma-
at least three different testing times (such as 30, 90, and 180
terials with a very high resistance to water-tree growth may
days) should be used to verify their comparative performance
require a longer time under test conditions (such as 180 days)
and disclose their kinetic nature of water-tree growth. Of
orhighervoltage(suchas10or15kV)inordertodifferentiate
course, it is also assumed that all water-treed regions are
their performance. For materials with a very low resistance to
water-tree growth, electrical breakdown may occur during the oxidized regions that can be stained for optical observation.
30-day testing time.Ashorter testing time (such as one or ten Different materials may also have different temperatures and
FIG. 1 Test Specimen Mold Cavity
´1
D6097 − 01a (2008)
times to stain the oxidized (treed) regions due to their different support assembly is carefully screwed into the base until the
softening temperature. needlepointextends3.2 60.1mmabovethesurface.Fig.1is
an example of the mold cavity.
6. Apparatus
6.4 Specimen Holder— The specimen holder, designed to
6.1 Power Supply—Ahigh-voltagesupplywithasinusoidal
holdatleasttenspecimens,ismadefromasolidblockofclear
voltage output of at least 5 kV at a frequency of 1 kHz and an
polymethyl methacrylate (PMMA). The PMMA is used be-
output power of 3 kVA.
cause of the ease of machining and its good electrical proper-
6.2 Conical Needles— Conical needles are made from steel
ties. The inside is machined to a depth of 50.8 mm with a
ortungstencarbide.Theirdimensionsare14.5 60.5mmlong,
12.7-mm wall thickness. The outside bottom has the same
4 6 0.2 mm in diameter, point radius of 3 6 1 µm for the
number of holes with an inside diameter of 25.4 mm with a
needle tip radius, and 60 6 1° point angle.
depth of 6.35 mm, drilled with a spacing of 38.1 mm from
6.3 Test Specimen Mold—The test specimen mold is a
center to center of the holes. The inside bottom has the same
three-layer metal mold. The top metal plate is flat. The center
holes with an inside diameter of 12.7 mm and a depth of 6.35
plate has at least ten holes to make ten test specimens for each
mm in line with the centers of the holes drilled at the outside
material. Each hole has a 25.4-mm diameter and at least
bottom. Fig. 2 is an example of the specimen holder.
31.75-mm spacing from center to center of each hole. The
6.5 Electrodes—Theelectrodeismadefroma1-mlengthof
centerplatealsohastheguideholesabout8mmindiameterat
24 AWG nickel-chromium wire or other suitable conductive,
two corners to mate with pins in the bottom plate section. The
noncorrosivemetalwireformed,ononeend,intoaclosedloop
bottom plate section consists of two metal plates bolted
about 50 mm smaller in diameter than the inside diameter of
together. The first bottom plate has the same number of holes
as the center plate. Each hole has the inside diameter of 4 mm the specimen holder with the remainder bent perpendicular to
to accommodate needles. The second bottom plate has the the loop so that it can be connected to the transformer to
holes with an inside diameter of 10 mm. The center points of
conduct the voltage into the electrolyte (the salt solution).
all the holes in the bottom and center plates are matched and
6.6 Water Bath—A circulating water bath; provided with
aligned.Theseholesatthesecondbottomplatearethreadedto
heaters and temperature controls if tests are to be made at
accommodate the needle support member. The needle support
elevated temperatures.
memberisfabricatedfromthreadedstainlesssteelroddrilledat
one end to provide a snug fit for needles, and at the other end
NOTE 1—Circulation of the solution in the bath even at room tempera-
to accommodate an hexagonal head driver. Needles are
ture is necessary to remove gas bubbles formed at the interface of the
threaded into the support member. The needle and needle solution and the test specimens caused by electrolysis.
FIG. 2 PMMA Specimen Holder
´1
D6097 − 01a (2008)
6.7 Microscope—A microscope equipped for 20 and 100× Warning—Water in the test tank is gradually evaporated.
magnification. Keeping the water level constant is important to prevent an
electrical hazard.
7. Reagents
9. Sampling
7.1 Salt—Reagent-grade sodium chloride.
9.1 Sample in accordance with Practice D1898.
7.2 Sealants—The material used for sealing in this test
method is a two-part silicone rubber sealant consisting of a
4 4
10. Test Specimen
base and a catalyst.
10.1 Geometry of Test Specimens —The test specimen is a
7.3 Multipurpose Silicone Sealant —One-partsilicone rub-
disk containing a conical defect at the center of one side. The
ber sealant.
disk has a diameter of 25.4 mm and a thickness of 6.35 mm.
7.4 Staining Dye— The staining dye is a mixture of the
Thisconicaldefecthasadiameterof3.2mmandheightof3.2
methylene blue and sodium hydroxide.
mm with an included angle of 60°. The radius of the cone tip
7.5 Deionized Water, or distilled water.
is 3 6 1 µm. Fig. 3 is the geometry of the test specimen.
10.2 Preparation of Test Specimens —Compression mold
8. Hazards
ten specimens for each solid dielectric material using the
8.1 Warning—Lethal voltages are a potential hazard dur- preparation method described in Practice D1928. Use a pre-
ing the performance of this test method. It is essential that the drilled polyethylene terephthalate sheet over needles to cover
test apparatus and all associated equipment that may be the metal surface of the bottom section of the test specimen
electrically connected to it be properly designed and installed mold to prevent cross contamination from the previous mate-
for safe operation. rialresidue.Applyacolorlessmoldreleaseagenttoallsurfaces
of the center section of the mold, to prevent cross contamina-
8.2 Solidlygroundallelectricallyconductivepartsthatmay
tionfromthepreviousmaterialresidue.Themoldreleaseagent
be possible for a person to contact during the test. Provide
should not contain grease, wax, or silicone oil. Weigh a
meansforuseatthecompletionofanytesttogroundanyparts
sufficient amount of each sample and fill the mold with the
whichwereathighvoltageduringthetestorhavethepotential
material. Cover the material with a polyethylene terephthalate
for acquiring an induced charge during the test or retaining a
sheet under the top test specimen mold plate. Put the mold
charge even after disconnection of the voltage source. Thor-
assembly together, and place the entire mold assembly in a
oughly instruct all operators as to the correct procedures for
hydraulic press and complete the molding cycle.
performing tests safely. When making high-voltage tests,
particularly in compressed gas, oil, water, or aqueous solution, 10.3 Molding Conditions—For thermoplastic polyethylene,
it is possible for the energy released at breakdown to be the molding cycle is 5 min at a low pressure of 0.30 MPa, 2
sufficient to result in fire, explosion, or rupture of the test minatahighpressureof3MPaat160 65°C.Forcross-linked
chamber. Design test equipment, test chambers, and test polyethylene, the mold cycle is 5 min at 125 6 5°C at a low
specimens so as to minimize the possibility of such occur- pressure of 0.30 MPa, 2 min at 120 6 5°C at a high pressure
rencesandtoeliminatethepossibilityof personal injury. If the of 3 MPa, and 15 min at 175 6 5°C at the same high pressure.
potential for fire exists, have fire suppression equipment Coolthemoldinthepressat15°C/mintoambienttemperature.
available. See Practice D1928. Different materials may have different
FIG. 3 Water-Tree Growth Test Specimen
´1
D6097 − 01a (2008)
conditions for molding. For materials other than polyethylene, 11.5 Placing S
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
An American National Standard
e1
Designation:D6097–01 Designation:D6097–01a (Reapproved 2008)
Standard Test Method for
Relative Resistance to Vented Water-Tree Growth in Solid
Dielectric Insulating Materials
This standard is issued under the fixed designation D 6097; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
e NOTE—The units statement in subsection 1.2 was corrected and the warning in old Note 2 was moved into the text of 8.2
editorially in July 2008.
1. Scope
1.1 This test method covers the relative resistance to vented water-tree growth in solid non-blacktranslucent thermoplastic or
cross-linked electrical insulating materials. This test method is especially applicable to extruded polymeric insulation materials
used in medium voltage power medium-voltage cables.
1.2 The values givenstated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitation prior to use. For specific hazard statements see 8.1.
1.4 There is no similar or equivalent IEC standard.
2. Referenced Documents
2.1 ASTM Standards:
D 1898 Practice for Sampling of Plastics
D 1928 Practice for Preparation of Compression-Molded Polyethylene Test Sheets and Test Specimens
D 2275 Test Method for Voltage Endurance of Solid Electrical Insulating Materials Subjected to Partial Discharges (Corona)
on the Surface
D 3756 Test Method for Evaluation of Resistance to Electrical Breakdown by Treeing in Solid Dielectric Materials Using
Diverging Fields
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 water tree length (WTL), n—a maximum distance, in millimetres, of a path which is a tree-like micro-channel measured
paralleltotheelectricfieldfromtheaxisofthetipoftheconicaldefect.—themaximumlengthofastainedtree-likemicro-channel
path in millimetres, measured from the tip of the conical defect in the direction of the conical axis.
3.1.2 resistance to water-tree growth (RWTG)— a dimensionless value which is L divided by the WTL.
3.1.3 thickness of point-to-plane specimen (L), n—the vertical distance in millimetres from the tip of the conical defect to the
opposite surface of the solid dielectric material.
4. Summary of Test Method
4.1 Ten compression-molded discdisk specimens, each containing a conical-shaped defect, are subjected to an applied voltage
of 5 kV at 1 kHz and 23 6 2°C in an aqueous conductive solution of 0.011.0 N NaCl for 30 days. This controlled conical defect
iscreatedbyasharpneedlewithanincludedangleof60°andatipradiusof3µm.Theelectricalstressatthedefecttipisenhanced
and can be estimated by the Mason’s Hyperbolic point-to-plane stress enhancement equation. This enhanced electrical stress
This test method is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of Subcommittee
D09.12 on Electrical Tests.
Current edition approved May 10, 2001. Published July 2001. Originally published as D6097–97. Last previous edition D6097–97a.
Current edition approved May 1, 2008. Published July 2008. Originally approved in 1997. Last previous edition approved in 2001 as D 6097 – 01a.
Discontinued; see 1997 Annual Book of ASTM Standards, Vol 08.01.
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Annual Book of ASTM Standards, Vol 08.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
e1
D6097–01a (2008)
initiates the formation of a vented water-tree grown from the defect tip. Each treed specimen is stained and sliced. The water-tree
length and point-to-plane specimen thickness measured under microscope are used to calculate a ratio that is defined as the
resistance to water-tree growth.
5. Significance and Use
5.1 This is a laboratory test designed to simulate the growth of vented water-trees in the solid dielectric insulating material
initiated by a sharp protrusion at the insulating and conductive interface under a wet environment in a high electrical field.
Water-treeing is the phenomenon which describes the appearance of tree-like growth in organic dielectrics under an ac field when
exposed to moist environments. Two types of water-trees are formed. Bow tie trees (within the dielectric) and vented water-trees
formed from conductive/insulating material interface into the insulating material. The water-trees referred to in this test method
aretheventedtype.Theinsulatingmaterialisthesoliddielectricorganicmaterial.Theconductivematerialisthesaltsolution.This
salt solution is used on both sides of the insulating material to simulate the same inner and outer semiconductive shields saturated
with moisture between the insulation layer used in a medium-voltage underground power cable.
5.2 This test method provides comparative data. The degree of correlation with the performance in service has not been
established.
5.3 The standard test conditions are designed to grow a sufficient water-tree length for most solid dielectric insulating materials
ofinterestbeforeelectricalbreakdownoccurs.Materialswithaveryhighresistancetowater-treegrowthmayrequirealongertime
under test conditions (such as 180 days) or higher voltage (such as 10 or 15 kV) in order to differentiate their performance. For
materialswithaverylowresistancetowater-treegrowth,electricalbreakdownmayoccurduringthe30-daytestingtime.Ashorter
testing time (such as one or ten days) is recommended to prevent electrical breakdown during testing for those low water-tree
resistant materials.
5.4 Other voltages, frequencies, temperatures, aqueous solutions, and defects can be used to evaluate specific materials for
specificapplications.Temperaturesshouldnotexceedthesofteningormeltingpointofthematerialor10to15°Cbelowtheboiling
point of the salt solution. Any non-standard conditions should be reported along with the results.
k
5.5 Tree-growth rates generally increase with the test frequency. An acceleration factor due to frequency is given by ( f/60)
where f is the test frequency and k is between 0.6 and 0.7. The test frequency of 1 kHz is selected to accelerate the water-tree
growth. However, the chemical nature of oxidized products from water-treeing may be different at different frequency ranges.
The sole source of supply of the base, Dow Corning 3110RTV, the catalyst, Dow Corning RTV Catalyst S, and the sealant, Dow Corning Multipurpose Silicone Sealant
732, known to the committee at this time is Dow Corning, Inc., Midland, MI 48686. 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 committe, which you may attend.
FIG. 1 Test Specimen Mold Cavity
e1
D6097–01a (2008)
5.6 Two assumptions for this test method are: (1) all tested materials grow trees in the same power law kinetic manner and (2)
the time under test conditions of 30 days is long enough to establish the difference in water-tree growth. If there is a doubt, at least
three different testing times (such as 30, 90, and 180 days) should be used to verify their comparative performance and disclose
their kinetic nature of water-tree growth. Of course, it is also assumed that all water-treed regions are oxidized regions that can
be stained for optical observation. Different materials may also have different temperatures and times to stain the oxidized (treed)
regions due to their different softening temperature.
6. Apparatus
6.1 Power Supply— A high-voltage supply with a sinusoidal voltage output of at least 5 kV at a frequency of 1 kHz and an
output power of 3 kVA.
6.2 Conical Needles— Conical needles are made from steel or 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 µm for the needle tip radius, and 60 6 1° point angle.
6.3 Test- Specimen Mold—The test- specimen mold is a three-layer metal mold.The top metal plate is flat.The center plate has
at least ten holes to make ten test specimens for each material. Each hole has a 25.4-mm diameter and at least 31.75-mm spacing
from center to center of each hole. The center plate also has the guide holes about 8 mm in diameter at two corners to mate with
pins in the bottom plate section. The bottom plate section consists of two metal plates bolted together. The first bottom plate has
the same number of holes as the center plate. Each hole has the inside diameter of 4 mm to accommodate needles. The second
bottom plate has the holes with an inside diameter of 10 mm. The center points of all the holes in the bottom and center plates
are matched and aligned. These holes at the second bottom plate are threaded to accommodate the needle support member. The
needle support member is fabricated from threaded stainless steel rod drilled at one end to provide a snug fit for needles, and at
the other end to accommodate an hexagonal head driver. Needles are threaded into the support member. The needle and needle
support assembly is carefully screwed into the base until the needle point extends 3.2 6 0.1 mm above the surface. Fig. 1 is an
example of the mold cavity.
6.4 Specimen Holder— The specimen holder, designed to hold at least ten specimens, is made from a solid block of clear
polymethyl methacrylate (PMMA). The PMMA is used because of the ease of machining and its good electrical properties. The
inside is machined to a depth of 50.8 mm with a 12.7-mm wall thickness. The outside bottom has the same number of holes with
an inside diameter of 25.4 mm with a depth of 6.35 mm, drilled with a spacing of 38.1 mm from center to center of the holes. The
inside bottom has the same holes with an inside diameter of 12.7 mm and a depth of 6.35 mm in line with the centers of the holes
drilled at the outside bottom. Fig. 2 is an example of the specimen holder.
6.5 Electrodes—The electrode is made from a 1-m length of 24 AWG nickel-chromium wire or other suitable conductive,
noncorrosive metal wire formed, on one end, into a closed loop about 50 mm smaller in diameter than the inside diameter of the
FIG. 2 PMMA Specimen Holder
e1
D6097–01a (2008)
specimen holder with the remainder bent perpendicular to the loop so that it can be connected to the transformer to conduct the
voltage into the electrolyte (the salt solution).
6.6 Water Bath—A circulating water bath; provided with heaters and temperature controls if tests are to be made at elevated
temperatures.
NOTE 1—Circulation of the solution in the bath even at room temperature is necessary to remove gas bubbles formed at the interface of the solution
and the test specimens caused by electrolysis.
6.7 Microscope—A microscope equipped for 20 and 1003 magnification.
7. Reagents
7.1 Salt—Reagent-grade sodium chloride.
7.2 Sealants—The material used for sealing in this test method is a two-part silicone rubber sealant consisting of a base and
a catalyst.
7.3 Multipurpose Silicone Sealant —One-part silicone rubber sealant.
7.4 Staining Dye— The staining dye is a mixture of the methylene blue and sodium hydroxide.
7.5 Deionized Water, or distilled water.
8. Hazards Note2—
8.1 Warning—Warning—Lethal voltages are a potential hazard during the performance of this test method. It is essential that
the test apparatus and all associated equipment that may be electrically connected to it be properly designed and installed for safe
operation.
8.18.2 Solidly ground all electrically conductive parts that may be possible for a person to contact during the test. Provide
means for use at the completion of any test to ground any parts which were at high voltage during the test or have the potential
for acquiring an induced charge during the test or retaining a charge even after disconnection of the voltage source. Thoroughly
instruct all operators as to the correct procedures for performing tests safely. When making high-voltage tests, particularly in
compressed gas, oil, water, or aqueous solution, it is possible for the energy released at breakdown to be sufficient to result in fire,
explosion,orruptureofthetestchamber.Designtestequipment,testchambers,andtestspecimenssoastominimizethepossibility
of such occurrences and to eliminate the possibility of personal injury. If the potential for fire exists, have fire suppression
equipment available. Note3—
Warning—Warning—Water in the test tank is gradually evaporated. Keeping the water level constant is important to prevent
an electrical hazard.
9. Sampling
9.1 Sample in accordance with Practice D 1898.
10. Test Specimen
10.1 Geometry of Test Specimens —The test specimen is a disk containing a conical defect at the center of one side. The disk
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 3.2 mm with
an included angle of 60°. The radius of the cone tip is 3 6 1 µm. Fig. 3 is the geometry of the test specimen.
10.2 Preparation of Test Specimens —Compression mold ten specimens for each solid dielectric material using the preparation
method described in Practice D 1928. Use a pre-drilled polyethylene terephthalate sheet over needles to cover the metal surface
FIG. 3 Water-Tree Growth Test Specimen
e1
D6097–01a (2008)
of the bottom section of the test specimen mold to prevent cross contamination from the previous material residue. Apply a
colorless mold release agent to all surfaces of the center section of the mold, to prevent cross contamination from the previous
material residue. The mold release agent should not contain grease, wax, or silicone oil. Weigh a sufficient amount of each sample
and fill the mold wi
...
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