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Reference: ISH2015_451

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Experiences with Application, Diagnostic Value and Impact on Asset Management of Insulation Oil Analysis



This paper presents and discusses the Swiss experiences with the application, analysis, value and impact on asset management of regular insulation oil diagnostics, which includes dielectric-chemical parameters, dissolved gas analysis and furan analysis. Most frequently oil laboratories determine the dielectric-chemical parameters according to IEC 60422. Here the interfacial tension, neutralization number (acidity), colour number and dielectric dissipation factor tangent delta (conductivity) allow for collecting a consistent record – even over decades – on the ageing performance of the observed oil-paper-insulation. This is not true for moisture content and breakdown voltage. Though these parameters are closely linked to each other (moisture strongly influences breakdown voltage), the authors could not establish a dependable relationship between these two parameters and the other ageing indicators. As for the limits given by standards, the authors observed that for most insulation oils the parameter interfacial tension (with 20 mN/m according to IEC60422) is the first which does not meet the requirements of the standards. Other parameters follow only after decades of operation. Therefore we conclude that the present limit is too high and propose to lower it. For the DGA (dissolved gas analysis) the paper presents the 90 % values of oil-filled HV equipment in Switzerland, grouped by power transformers and instrument transformers. These values are mostly lower than given in IEC60599. The most frequent DGA failure type is local hot spots, indicated by excessive production of ethylene. This is followed by partial discharge activity.

File Size: 712,8 KB

Year: 2015

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