Abstract: The structural elements within power transformers are commonly constructed from high-density pressboard, chosen for its favourable mechanical and dielectric properties. Among these elements are the spacers employed in the windings of transformers, which endure compressive loading during operation. The spacers are immersed in dielectric fluid and exposed to high temperatures and chemical reactions over the transformer's lifespan, resulting in the degradation of their dielectric and mechanical properties. The mechanical integrity of the power transformer significantly relies on these factors; hence, it is imperative to comprehend how ageing deteriorates the mechanical response of the high-density pressboard. The present article presents experimental data on the compressive mechanical properties of a commercially available high-density pressboard, commonly employed in power transformer spacers, under various ageing conditions (induced through accelerated thermal ageing and assessed by the degree of polymerisation). These data hold potential for diverse applications. They can enhance the existing comprehension of the mechanical behaviour and degradation mechanisms of cellulosic insulation in power transformers and provide reference benchmarks for comparison with factory-obtained values by manufacturers. In the realm of engineering failure analysis, these values can be utilised to evaluate the mechanical failures of paper-based materials utilised as structural components in power transformers.

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