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Measurement and analysis of dielectric response in oil-paper insulation systems /

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ABSTRACT Diss. no. 12832 techn. sc. SFIT Zurich. Literaturverz.

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    ABSTRACT: This paper starts with a systematic benchmark test of the three commercialised dielectric diagnostic methods RVM (recovery voltage method), PDC (polarisation and depolarisation currents) and FDS (frequency domain spectroscopy), performed on a large transformer model. The water content as analysed by the specific software was compared under three parame-ters: insulation geometry, insulation temperature and oil conductivity. It was found, that for the RV method the interpretation scheme based on the central time constant is too simplistic. The other two methods PDC and FDS compensate much better for the mentioned parameters but nevertheless analyse a drier cellulose with increas-ing temperature and a wetter cellulose for increasing oil conductivity. Actually the moisture in cellulose re-mained constant at 1 % during all the tests. Starting from these weaknesses a more sophisticated software was developed. The new software called "Dirana" bases on a new data pool, measured at new and aged press-board with various moisture contents, temperatures and oil impregnation. The analysis algorithm works in fre-quency domain and features weighting of low frequency data and an extended XY-model for analysing oil-paper-insulations. Results obtained from this software show especially a much better compensation for varying oil conductivities and insulation geometries. The new soft-ware was successfully utilized for a on-site measure-ment in comparison to other measurement methods.
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    ABSTRACT: This paper presents a study on the characterization of aging of transformer oil–pressboard insulation. Traditional and modern diagnostic tools and techniques were used to investigate aging of oil–paper insulation under controlled laboratory conditions. Insulation condition testing includes common chemical diagnostics such as acidity tests and new chemical techniques: determination of relative content of dissolved decay products by spectrophotometry, solid suspension by turbidimetry, Fourier Transform Infrared (FTIR) spectroscopy and electrical diagnostic techniques that have gained exceptional importance for utility professionals: polarisation/depolarisation current, recovery voltage measurement and frequency domain dielectric spectroscopy measurements. From the obtained results it is found that chemical tests depicted more sensitivity to insulation degradation. Also, different oil–pressboard insulation ratios were investigated to assess the influence of the relative amount of cellulosic materials on aged mineral oil decay products and vice versa. Emphasize is laid on the potentialities/avenues offered by FTIR to assess oil insulation condition. Notable experimental results have been reported, which could be valuable to researchers and practicing engineers in this field.
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