AEMC 6503 - 4.4 Successful Insulation Resistance Testing

14 MegohmmeterModels6501/6503
4.3.3 Ratio Testing
In time resistance reading (Dielectric Absorption Ratio), readings
are taken at 30 seconds and 60 seconds to obtain the dielectric
absorptionratio.
 Insulationresistance@60s
 Insulationresistance@30s
Thistestisusefultoincreasetheaccuracyofspottesting.Ingen-
eral,aratioof1.25:2orbettershouldberequired.Aratiobelowthis
indicatesthatrepairisprobablyneeded.
Rememberthata DCinsulationtestmaybeusedfor acceptance
testing,butismorecommonlyusedtocheckthegradualdeteriora-
tionofequipmentoveritslife.Consultyourequipmentmanufacturer
forspecictestortestvoltageifnotknown.
Insulationresistancedecreaseswithmoisture,temperatureandage
andshouldberecordedovertimeatagiventemperatureandcor-
rected.
4.4 SuccessfulInsulationResistanceTesting
• Checkwiththeequipmentmanufacturerforfactoryinsula-
tionresistancereadings.
• Donotrelyoninsulationresistancetestingaloneasproof
ofwindingconditions.
• Donotexpectthesamevalueforallpartsofallmachines.
• Observeconsistenttesttimeduration,recognizingthat
totalcurrentthroughinsulationundertestwillvarywith
time.
• Correctallreadingsproperlytoastandardreferencetem-
perature(seeIEEEstd#43-2000,Temperature Correction
Curve).
• Knowwhatyouaretesting.Isolatethepieceofequipment
fromothercircuitry.
• Watchtrendsratherthanrelyingonsingle“spot”readings.
=DielectricAbsorptionratio
(DAR)
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