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Theexperimentswereperformedontwotypesofspecimensthatrepresentedhigh-
voltagecableinsulation.Thefirstone,denotedas(PK),representstheinsulatingpaper,
whilethesecondone(XLPE)representsthecross-linkedpolyethylene.Bothspecimens
containedthesamesizeoftheembeddedvoidshowninFigure3.9.Theelectricalprop-
ertiesofthespecimens(specifically,permittivityandresistivity)areshowninTable3.1.
Table301
Electricalpropertiesofspecimens
Surfaceresistivity[Ω]
Volumeresistivity[Ωl⋅lm]
Relativedielectricpermittivity
800⋅10
101⋅10
Glass
709
10
11
200⋅10
406⋅10
PK
208
12
13
2⋅10
6⋅10
XLPE
204
13
14
InordertoinvestigatetheinfluenceofinsulatingmaterialresistivityonPDincep-
tion,thefollowingfourspecimenswerecompared:
a)wholespecimenmadeofinsulatingpaper(PK–layers1and2);
b)wholespecimenmadeofpolyethylene(XLPE–layers1and2);
c)voidLayer2madeofXLPE,andtop/bottomlayers1madeofinsulatingpaper(PK);
d)voidLayer2madeofPK,andtop/bottomlayers1madeofpolyethylene(XLPE).
Thegeometryofthespecimenswaskeptconstantforalloftheaboveconfigura-
tions.Inallofthesecases,layer0referstotheglassplate.Thegraphicalrepresentation
ofthespecimensisshowninFigure3.11.
a)
b)
c)
d)
Fig030110Graphicalrepresentationofspecimenconfigurations:a)insulatingpaper(PK);
b)XPLE;c)top/bottominsulatingpaper,voidlayerXLPE;
d)top/bottomXLPE,voidlayerPK
Forreference,thepartialdischargeswerefirstmeasuredatACvoltage;then,the
sequenceatDCvoltagewasrecorded.Thepartialdischargeinceptionvoltagethresh-
olds(PDIV)obtainedbothfromthecalculations(Equations(3.23)and(3.24))and
measurementsareshowninTable3.2.ThesymbolofPK-XLPE-PKusedinthispaper
translatestoXLPEvoidlayermaterialandPKtop/bottomlayers.Thesolesymbolsof
PKorXLPEdenotethespecimensthatweremadeentirelyfromtherespectivehomog-
enousinsulatingmaterials.
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