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

Abstract

The development of reliable, environmentally safe and economic insulating oil for the transformer is an endless effort of the electrical industry. Recent research is based on natural ester fluid, the green insulating oil which exhibits excellent dielectric performance and environment friendly characteristics. Nanofluids are also emerging as potential replacement for the conventional mineral oil used in transformers. Characterisation of nanoparticle filled mineral oil and natural esters have validated their improved dielectric behaviour in comparison to the unfilled oil. Although the applications are wide, the state of the art technology requires a deeper understanding of the underlying phenomenon. Much work is expected to be done in the application of nanofluids prepared with mineral oil and natural ester, particularly its effect on the cellulose insulation. The study provides an overview of the different materials that have been used as alternatives to the conventional transformer mineral oil, with special emphasis on natural esters and natural ester nanofluids, their advantages and challenges.

Analysis of the application of Insulating Vegetable Oil in electric power distribution transformers

“…The history of the transformer began in 1855 with a patent granted to Addenbrooke and Ferranti, and since 1890 the IMO has been used in transformers and remains, today, the most used liquid dielectric in transformers in association with insulating paper [8,10,26]. General Electric produced the first recognized application of the IMO in transformers in 1892, turning the attention of the industry to determine the properties necessary for it to be used [26,27].…”

“…The popularity of the use of this oil occurred due to its low cost and its wide availability, obtained from the fractional distillation of oil, in addition to its excellent dielectric properties [10,26]. According to [28], IMO has been used as an insulating liquid in transformers for over a hundred years, reaching billions of liters of oil being used in electrical equipment worldwide.…”

“…The IMO consists basically of hydrocarbons [6] (molecules composed of Hydrogen and Carbon) with concentrations of other compounds, such as Sulfur, Nitrogen, among others [29]. Because of this composition, its leakage or spill can have significant environmental impacts, since it contaminates the soil and the water system, bringing economic impacts to the electric utilities [10,26]. Currently the mineral oil used can be naphthenic or paraffinic based, where naphthenic based is the most used, because it has good characteristics of thermal conductivity, high flash point, low cost of large-scale production, high regeneration capacity, great amount of physical-chemical tests, facilitating their maintenance, among others [10,21,24].…”

“…According to [7,26,29], the paraffins or alkanes material are saturated hydrocarbons of straight or branched open chain, thus, the paraffin-based oil has molecules arranged in a different structure from the naphthenic base. The structure of the paraffinic chain is shown in Figure 4.…”

“…These mineral oils tend to form short-chain organic acids with by-products of degradation consisting of hydrocarbons that are harmful to the environment regardless of whether the oil used is paraffinic or naphthenic [27,29]. These hydrocarbon compounds can migrate to the water table with rainwater infiltration, where one liter of oil can contaminate millions of liters of water, making it unfit for consumption [21,26]. The [29] show that the potential for contamination of a fluid is measured by its level of biodegradability, governed by the standard that determines these values, the Organization for Economic Cooperation and Development (OECD 301) [31], where for mineral oil, its level of biodegradability is around 10%, that is, it is not very biodegradable.…”