Water uptake rates of transformer paper insulation impregnated with vegetable oil

Vegetable oil-based dielectrics have been available for the past 15 years; relevant articles have been published [1]-[3]. One practical advantage of using a vegetable-oil dielectric in a power transformer is its higher affinity to moisture, around 20 times higher than that of mineral oil at room temperature [4]. Power transformers containing vegetable oil are usually sealed, preventing water ingress from the air. However, during manufacture, installation, or servicing, the transformer cellulose structure is likely to be exposed to the air. The rate at which a vegetable oil absorbs moisture from the air, and hence the time for which transformer paper insulation impregnated with a vegetable oil dielectric can be exposed to air before it becomes too wet to function satisfactorily, is of considerable interest to power utilities. In this article we compare the water uptake rates of insulation paper impregnated with FR3 vegetable oil with the corresponding rates for mineral oil.