ELECTRICAL AND CHEMICAL DIAGNOSTICS OF TRANSFORMERS INSULATION .B. ACCELERATED AGED INSULATION SAMPLES

This paper describes the analysis of accelerated aged insulation sampl es to investigate the degradation processes observed in the insulation from aged transformers. Short term accelerated ageing experiments wer e performed on paper wrapped insulated conductors and on pressboard sa mples. The condition of aged insulation samples was investigated by tw o relatively new diagnostic techniques: (a) measurements of interfacia l polarization spectra by a DC method (b) measurements of molecular we ight and its distribution by gel permeation chromatography. Several ot her electrical properties of the paper/pressboard samples were also st udied. Possible correlations have been investigated among the differen t measured properties. The GPC results have been used to predict how m olecular weights change with temperature and time.