Study on the effect of impulse voltage withstandability on the thermally-aged transformer paper

Transformers play an important role in power transmission. It is, therefore, necessary to know the condition, once the transformer becomes aged. Presently, residual life assessment (RLA) methods are being extensively used to know its condition. The insulation system of a transformer consists of mainly oil and paper; and hence, the conditions of these two materials are critical for reliable operation of transformer. Methodologies are available for RLA studies using different parameters like dissolved gas analysis (DGA), furfural content, and degree of polymerization (DP) etc. However, it is also necessary to study the impulse withstandability of cellulose paper and establish its relationship with DP. In this paper, the effect of ageing of cellulose paper on DP, dielectric strength and impulse withstandability has been studied and a methodology has been developed to know the condition of paper vis-a-vis the impulse withstandability and dielectric strength.