State-of-the-art review on the performance of cellulosic dielectric materials in power transformers: Mechanical response and ageing

Power transformers are essential elements in electrical systems and the end of their useful life is frequently conditioned by the state of the cellulosic insulation materials inside them. These materials are subjected to high temperatures and mechanical stresses, primarily generated by short-circuits or inrush currents. Moreover, both the cellulosic materials and the dielectric oil in which they are impregnated are affected by chemical reactions. In order to achieve a better understanding of ageing kinetics and improve the management and planning in electrical systems from a technical and economical point of view, it is important to better understand the behaviour of cellulosic insulation. The purpose of this review is to analyse the current state-of-the-art with reference to the modelling of the mechanical behaviour of paper materials used as insulation in power transformers, as this topic has been previously analysed in many different publications but only fragmentarily. A suitable model for transformer cellulosic insulation, in combination with engineering measurements, could help to optimise the design of the insulation and manufacturing processes, as well as to accurately predict the end-of-life of power transformers.