Study on the Contamination Rate of Mineral Oil in Natural-Ester Retrofilled Transformers

Montero, Andrés; García, Belén; Burgos, Juan Carlos

doi:10.1109/tdei.2023.3298314

Cited by 2 publications

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“…Although there is agreement on the fact that cellulose insulation ages more slowly in the presence of an ester, it is not so clear that this result can be extrapolated to the insulation of retrofilled transformers. Experimental evidence on this fact is mainly based on laboratory accelerated ageing tests carried out on cellulose-ester systems, but the liquid insulation of retrofilled transformers is a mixture of mineral oil (MO) and natural (NE) or synthetic ester [7][8][9], the MO being the material that remains mostly adsorbed in the paper [10,11].…”

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confidence: 99%

Life Expectancy of Transformer Paper Insulation Retrofilled with Natural Ester in the Laboratory

Montero,

García,

López

2023

Polymers

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The use of alternative insulating liquids instead of mineral oil in transformers is spreading around the world due to their superior fire resistance. Furthermore, researchers have demonstrated that these oils increase the lifespan of the solid insulation of the transformers and, thus, the life expectancy of the equipment. Retrofilling of transformers with natural and synthetic esters allows companies to benefit from the properties of using these liquids without making an investment into new machinery. This paper investigated the ageing process of Kraft paper that was retrofilled with a natural ester in the laboratory. The Kraft paper samples were subjected to accelerated thermal ageing in an oven at 130 °C, and markers such as the degree of polymerisation and tensile strength were measured. The ageing tests comprised a first period, where the samples were immersed in mineral oil, followed by a replacement of the oil with a natural ester. As moisture is a determinant factor for paper ageing, two sets of samples with different moisture contents were tested. The results showed that the retrofilling of the transformers may slow down the degradation rate of the solid insulation despite the presence of remaining mineral oil adsorbed in the paper.

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