Investigating the effects of oxidation and thermal degradation on electrical and chemical properties of power transformers insulation

This paper describes the analysis of thermally accelerated aged insulation samples to investigate the degradation processes observed in the insulation of aged transformers. Accelerated ageing experiments were performed on pap er wrapped insulated conductors in the presence of air and nitrogen environ ments over a temperature range of 115 to 145 degrees C. Effects of oxidatio n on the ageing of oil-paper insulation were investigated and results are p resented in this paper. The condition of aged insulation samples was invest igated by a number of diagnostic techniques: (a)measurements of interfacial polarization spectra by the return voltage method (b) measurements of mole cular weight and its distribution by gel permeation chromatography, (c) sur face analysis by X-ray photo-electron spectroscopy and (d) a study of the o xidation of the oil by UV-visible spectroscopy. Results from these measurem ents are presented in this paper and are used to analyse the degradation pr ocess with special emphasis on oxidation.