Review on ester based dielectric liquids for transformer insulation technology

Abstract

Ester based dielectric fluids were found to beat mineral oils in thermal and environmental aspects. Hence there is a great need of research on ester oils. The present paper is a review of 84 published articles. Owing to length of the document; exceptions were made to include a citation if a publication contributed a significantly technical viewpoint on usage of ester oils for transformer insulation technology. The selected literature has been classified into relevant sections to make researchers convenient in obtaining literature. Some citations spanned for more than one section, efforts were made to include such citations in one of the most relevant section. The present paper will be useful to the industry and researchers to know the significance and need of ester based dielectrics to the present day scenario.

Research progress in modified mineral oil, natural ester and mixed oil in transformers

“…NEs are 100% biodegradable and belong to the K2 class liquids with high fire safety compared to MOs which are O1 class liquids 47–49 . However, the permittivity, viscosity, and dissipation factor of NE is all higher than that of MO.…”

Review on natural ester and nanofluids as an environmental friendly alternative to transformer mineral oil

“…The major disadvantage of mineral oil is its inflammable and toxic nature. Natural esters are 100% biodegradable and belong to the K2 class liquids with higher fire safety (higher limits for flash point and fire point) compared to mineral oils which are O1 class liquids [13, 39]. The distance of separation of an ester filled transformer from other transformers or buildings is only 1/10th of the distance for mineral oil based transformers, which promotes its safe usage in highly populated areas.…”

On Some Imperative IEEE Standards for Usage of Natural Ester Liquids in Transformers

“…The comparison cannot be made directly between these two liquids because the mechanisms are different. Indeed, the polarity of the triglyceride molecules present in natural ester leads to a slightly higher dissipation factor than mineral oil [14]. The formation of acids caused by intermediate species in mineral oil is due to an increase in its dissipation factor.…”

“…It is inferred that; higher acidity of esters may be otherwise understood as a degree of dryness of the insulating paper whereas higher acidity in mineral indicated the formation of sludge in the oil [14]. Hence, one may consider the acid number of mineral oils to decide with the reclamation and replace action while acid number alone is not capable of deciding this action in the case of ester liquids.…”