Dielectric Performance of Natural Ester Insulating Fluids as a Sustainable Alternative to Mineral Transformer Oil: A Systematic Review

Ude Kingsley Okechukwu; Ugwu Kelvin Ikechukwu; Mmamel Ngozi Juliana; Nnamani; Micheal Obiora

doi:10.56201/wjimt.v10.no8.2026.pg221.235

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Dielectric Performance of Natural Ester Insulating Fluids as a Sustainable Alternative to Mineral Transformer Oil: A Systematic Review

Ude Kingsley Okechukwu, Ugwu Kelvin Ikechukwu, Mmamel Ngozi Juliana, Nnamani, Micheal Obiora

Abstract

The increasing demand for environmentally sustainable, fire-safe and technically reliable transformer insulation has intensified interest in natural ester insulating fluids as alternatives to conventional mineral transformer oil. This review critically evaluates the dielectric performance, moisture behaviour, ageing characteristics, environmental sustainability and practical applicability of natural ester insulating fluids in power transformers. The review synthesizes published evidence on key performance parameters, including AC breakdown strength, impulse withstand capability, streamer behaviour, partial discharge, dielectric losses, moisture interaction, thermal ageing, oxidation stability and cellulose insulation degradation. Particular attention is given to the factors responsible for variations in reported performance, including fluid formulation, temperature, moisture content, electrode configuration, electrical stress and ageing conditions. The findings indicate that natural ester fluids generally provide competitive dielectric performance while offering significant advantages in fire safety, biodegradability, renewable- resource potential and moisture management. Their high moisture solubility can facilitate moisture redistribution from cellulose insulation and may contribute to improved insulation ageing performance. However, oxidation stability, viscosity, temperature-dependent behaviour and the limited availability of long-term field data remain important challenges. Evidence also indicates that natural ester transformers require condition-monitoring and diagnostic approaches that are attuned to their particular electrical and chemical properties, especially for dissolved gas analysis and partial discharge assessment. From a sustainability perspective natural ester offer significant environmental benefits, although their overall sustainability needs to be assessed from a lifecycle perspective including feedstock production, processing, transport and end-of-life management. Nigeria has specific opportunities with high ambient temperatures, fluctuating transformer loading, environmental concerns, growth in renewable energy and the availability of agricultural oil resources providing a solid basis for further investigation. The review concludes that natural ester insulating fluids represent technically viable and environmentally attractive alternatives to mineral transformer oil, but their broader adoption should be supported by standardized testing, long-term field studies, ester-specific diagnostic criteria, lifecycle economic assessment and climate-specific research. A progressive pathway involving laboratory validation, prototype testing, pilot deployment and long-term monitoring is recommended for sustainable adoption.

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Dielectric Performance of Natural Ester Insulating Fluids as a Sustainable Alternative to Mineral Transformer Oil: A Systematic Review

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