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 paper wrapped insulated conductors in the presence of air and nitrogen environments over a temperature range of 115 to 145°C. Effects of oxidation on the ageing of oil-paper insulation were investigated and results are presented in this paper. The condition of aged insulation samples was investigated by a number of diagnostic techniques: measurements of interfacial polarization spectra by the return voltage method; measurements of molecular weight and its distribution by gel permeation chromalography; surface analysis by X-ray photo-electron spectroscopy; and a study of the oxidation of the oil by UV-visible spectroscopy. Results from these measurements are presented and are used to analyze the degradation process with special emphasis on oxidation