Kraft And Diamond Dotted Paper Thermally Aged In Mineral Oil And Natural Ester: Mechanical Characterisation

Abstract

Oil-immersed transformers, whose lifespan is defined by cellulose insulation's lifetime, utilize frequently mineral oil. However, this insulating fluid is being replaced by alternative liquids such as natural and synthetic esters. This replacement requires to guarantee a similar behavior of solid insulating materials immersed in them. Although there are different authors who have concluded that Kraft paper reduces its deterioration rate when it is immersed in biodegradable fluids, there are few works that have analyzed the effect of insulation liquids on the mechanical properties of other cellulosic materials such as diamond dotted paper (DDP) during laboratory tests. This paper shows a comparative analysis of four paper/oil specimens (a standard Kraft paper and a diamond dotted paper aged in both mineral oil and natural ester) under controlled laboratory accelerated thermal ageing. This work focuses on changes in mechanical properties such as the energy consumed per unit volume of the failure zone (ER), rupture strength (σR) and strain under ultimate strength (εcm).

Impact of the Use of Vegetable Oil on the Mechanical Failure of the Cellulosic Insulation of Continuously Transposed Conductors in Power Transformers

“…There are numerous recent studies on the influence of vegetable oils in the chemical and dielectric properties of the transformer insulation, such as [5][6][7][8][9]. Nevertheless, there are only a few which analyse their impact on the mechanical properties of the solid insulation, for instance [10,11]. Thus, it can be claimed that there is a lack of understanding about how the ageing process with vegetable oils affects the mechanical performance of the dielectric paper in transformer components such as Continuously Transposed Conductors (CTCs), especially for papers different from Kraft type, such as crepe.…”