A review on critical evaluation of natural ester vis-a-vis mineral oil insulating liquid for use in transformers: Part 1

Abstract

In a long 130 years of its journey in service to mankind, the power transformer has grown in many aspects; ratings, performance, technology, aesthetics and ecofriendliness. Today, the transformer industry is witnessing the era of shifting from petroleum based mineral oils that are depleting, environmentally unfavorable, and proven dangerous to natural esters (vegetable oil based) that are renewable, environmentally friendly, and non-hazardous. The market and regulatory pressures to reduce liability risk exposure of mineral-oil-filled distribution and power transformers are increasing. In addition, there are demands to improve equipment efficiency and adopt more "earth-friendly" options in our power systems. In the last two decades there has been a resurgence of usage of natural ester insulating liquids for their "GREEN" and Safety credentials. These renewable resources have good dielectric properties and are compatible for use in power transformers. This paper evaluates and relates the new natural ester oil with existing mineral oil technology in terms of environmental concern, fire safety, physio-chemical properties, thermal performance, and dielectric performance. It also covers key modifications in design, manufacturing and operation to help assure excellent functionality and long life. In brief, this paper provides transformer designers and users about the advantages and challenges of "Green Insulating Liquid". Due to the voluminous properties that are compared and discussed, this paper is presented in two parts: Part 1 discusses on key properties and standards for the two liquids. Part 2 emphasizes on additional key properties and material compatibility related to electrical design. Based on evidence discussed in both parts, it is concluded that natural esters are acceptable for both new transformers and for retro filling existing units.

Development of a Biodegradable Electro-Insulating Liquid and Its Subsequent Modification by Nanoparticles

“…Rapeseed oil contains a high number of saturated fatty acids which make the oil oxidation stable and thus usable in long-term applications. As was mentioned above, the application of natural esters in transformers has several pros and cons [2,6,12]. The main advantage is their environmental compatibility, biodegradability and high flash (<200 • C) and fire points (<300 • C).…”

“…From these overviews is visible that it is difficult to apply natural esters without further transformer adjustments. However, if all these features are already included in the machine design itself, the potential of natural esters can be fully utilized e.g., in areas of increased environmental protection [6], such as shopping centers, protected natural areas, natural parks, proximity to water sources, etc. The next possibility for using a natural ester is retrofilling mineral oil transformers.…”

“…There are commercial products already used in the transformers [3,4], however, still, several technical problems prevent them from being deployed. Well know are problems with their higher viscosity (a heat transfer issue) [5], high pour point [6], higher permittivity [7], low oxidation stability [8] (a hermetic design is required) and the high price of commercially produced esters, etc. This is also the reason why currently such fluids are deployed in Europe sporadically, mainly in headquarters or showrooms of international corporations or in specially protected areas.…”

Numerical analysis of the hot-spot temperature of a power transformer with alternative dielectric liquids

“…In 2016, Mehta et al presents two reviews [22,23] in which many properties of both types of liquids are compared. As a result of this comparison, it is concluded that natural esters are acceptable for both new transformers and for retro filling existing units.…”

Evolution and Modern Approaches of the Power Transformer Cost Optimization Methods

“…However, there was a huge development in the cleaning and the manufacturing processes of the oils and in the applied additives [9,18,[45][46][47]. Basically, two types of mineral oil based transformer oil are used: paraffinic-based and the naphthenic-based oils [48]. During the aging processes insoluble sludge has been produced in the case of paraffinic-based oils.…”