Use Performance and Management of Biodegradable Fluids as Transformer Insulation

Abstract

In recent years, the use of biodegradable fluids as liquid insulation for distribution and power transformers is spreading. The main biodegradable fluids used are natural and synthetic esters, although biodegradable hydrocarbons have been recently proposed. Biodegradable fluids have a much lower environmental impact than mineral oil, limiting the risk of soil contamination in leaks, which makes them a suitable solution for applications such as offshore transformers or railway transformers. Additionally, these fluids have a higher flash point than conventional mineral oils, which dramatically reduces the risk of fire and collateral damage derived from explosion and fire. Despite these advantageous factors, there are still some aspects that hinder the broadening of their use, such as the difference in thermal properties or the lack of accepted maintenance procedures for transformers that use them as liquid insulation. This paper presents the current status of biodegradable insulating fluids, analyzing some of their properties and discussing the aspects that are still to be investigated in order to make them a real alternative to petroleum-based fluids.

Evaluation of Thermal Properties of Various Insulating Liquids Used in Power Transformers

“…There are many research results in the literature showing that mineral oil has better thermal properties than esters [30][31][32][33][34][35][36]. This claim is supported by comparative results of tests of both materials as a liquid filling the remaining volume of the transformer.…”

“…The articles [30,31] prove the influence of the type of liquid (esters, oil) on selected thermal properties such as viscosity, density, specific heat and thermal conductivity. The paper [32] shows that the addition of nanoparticles changes the density, viscosity and thermal conductivity of oil and esters.…”

Thermal Ageing of Dry Cellulose Paper Impregnated with Different Insulating Liquids—Comparative Studies of Materials Properties

“…Currently, alternatives to mineral oil are mainly synthetic and natural esters [3,4]. These liquids are increasingly used in low-and medium-voltage distribution transformers and occasionally in grid and step-up transformers.…”

“…The greatest advantage of these liquids, compared to mineral oil, is their good fire properties, including high flash and fire points [5,6]. Furthermore, synthetic and natural esters are considered environmentally friendly liquids due to their biodegradability [4,7].…”

Numerical Simulation of 35kV Oil-Immersed Transformer Fire and Extinguishing Effects of High-Pressure Fine Water Mist

“…Insulation oil is the main insulating and cooling medium for oil-immersed transformers, which are filled with large quantities of combustible transformer oil inside and on top of the oil pillow. Oil-immersed power transformers in the long-term operation process, its internal insulating oil paper will be affected by electrical, thermal, mechanical stress and other factors and gradually deteriorate, resulting in its insulation performance decline, in the fault, high temperature conditions fire, often leading to oil-immersed transformers themselves and other adjacent electrical equipment damage, serious damage to substations, once a fire will not only affect the safe and stable operation of the power grid, and even to the safety of society has a great impact [6][7][8][9][10][11][12]. In a 220kV transformer fire true type experiment, the temperature around the fire was up to 800℃, causing serious damage to the facilities around the substation [13].…”