Diagnostic testing of power transformer insulation by response measurements in frequency domain

Abstract

This paper presents results of frequency domain response measurements on field-aged power transformer insulation comprising oil and cellulose material (paper. pressboard. etc.). Different types of oil-paper insulated power transformers were selected from the hydropower stations in Sri Lanka. The loss tangent of the transformer insulation was measured over a broad frequency range. It is shown that the variation of loss tangent over frequency provides an easy classification of new and aged transformers.