The mineral or synthetic oil is mostly being used in conjunction with paper as the dielectric medium in most of the high voltage equipment. However, impact on environment, lack of petroleum oil reserves and disposal problems with used oils, have prompted researchers to direct their focus onto biodegradable and renewable insulating materials. The new insulating liquid materials development is guided by multiple factors such as environmental requirements and other safety and economic considerations. Therefore transformers manufacturer have to face new specifications related to these new requirements. The Vegetable-oil based transformer fluids increasingly replacing mineral oil-based products in the market place. They are successful because they perform better than mineral oil products and they provide definite environmental and safety gains. This paper reviews the current status of vegetable oils use as transformer oil, including their production, processing, and characterization. The vegetable oils most used as transformer oils are presented and their main advantages described in comparison with mineral oil. The various experimental work carried out in different countries is described, giving an overview of the current research carried out on the vegetable oils. In addition scope and challenges being faced in this area of research are clearly described.

Use of vegetable oils as transformer oils – a review

Green insulating fluids are playing a vital role in insulation design of the distribution transformers. Traditionally used mineral oil has lesser biodegradable and low fire resistant characteristics. Hence, it does not satisfy the new environmental regulation. Besides that, the availability of fossil fuels is also going to run out. These negative aspects motivate to search for an alternate insulating oil. This research has been proposed for feasibility study on non - edible pongamia pinnata oil as an alternate liquid dielectric which can be used in Distribution Transformers. The paper also reviews the alternate insulating oil, electrical, physical and chemical properties. Subsequently, Pongamia Pinnata Oil's electrical properties (Dielectric Strength, Dielectric Constant, Dielectric Dissipation Factor and Specific Resistance), chemical properties (Water content, Acidity) and physical properties (Viscosity, Flash Point, Interfacial Tension) have been estimated according ASTM and IEC for comparing the Pongaima Pinnata oil with conventional mineral oil. Alongside, solid insulating material deterioration, both in pongamia pinnata oil and mineral oil, using XRD and SEM was carried out. The experiments are encouraging. If the oil suited for these characteristics the value addition has been made from this oil which leads to waste land utilization and rural development.

A critical review on the characteristics of alternating liquid dielectrics and feasibility study on pongamia pinnata oil as liquid dielectrics

Review of vegetable oils behaviour at high temperature for solar plants: Stability, properties and current applications

The research for new mineral oil substitutes focuses on vegetable oils known for their biodegradability and low toxicity. This paper focuses on the development and analysis of physicochemical and dielectric properties of a bio-based insulating liquid from castor oil. Castor oil is an inedible tropical resource. It has a good annual oil yield and is widely available in developing countries. Cold pressing of castor seeds is the most appropriate non-chemical process for extracting oil. A refining process was used to remove metal and chemical residues. Refined Castor Oil was filtered and degassed in order to minimize the dissolved gases, solid particles and moisture. A transesterification operation was performed to significantly reduce viscosity oil. Finally, obtained Castor Oil Methyl Esters (COME) are finally distilled in a rotary evaporator under vacuum to remove traces of water and methanol. Physicochemical properties as visual examination, relative density, kinematic viscosity, and acidity were measured in accord-ance with ASTM D6871. AC Breakdown voltage was performed according to IEC 60156, and had been analyzed using Weibull distribution. Processed Castor Oil (PCO) has low viscosity than certified transformer vegetable oils (BIOTEMP, FR3) and high Dielectric Strength (74.67 kV/2.5 mm). Partial Discharges characteristics including the Partial Discharge Inception Voltage and the Partial Discharge Propagation Voltage were also investigated according to the recommendations of IEC 61294. PCO has satisfactory properties for their use as an insulating oil for transformer.

Elaboration and Performance Analysis of a Bio-Based Insulating Liquid from Castor Oil for Power Transformers

The present work aims to develop a new vegetable insulating fluid for power transformers based on Jatropha curcas oil. Besides its technical benefits, Jatropha curcas oil has a socio-economic role by promoting income to rural families, contributing to the countryside development and avoiding rural exodus. Thus, the entire transformer oil production (extraction, processing, characterization and accelerated aging) was covered and a new process was developed. For oil extraction, the most suitable process was the solvent extraction (5 mL of hexane per gram of crushed non-peeled seeds during 30 minutes) with an oil yield of 32%. In raw oil processing stage, the degumming, with 0.4 g of phosphoric acid per 100 g of oil, at 70°C, was used to remove phosphatides. Then, free fatty acids were 96% neutralized with a sodium hydroxide solution (0.5% w/w) at room temperature. For the oil clarification, the combination of 5% w/woil of activated carbon and 1% w/woil of MgO resulted in a bright, odorless and clear oil with an acid number of 0.04 mgKOH·g﹣1. The oil drying in a vacuum rotary evaporator, at 70°C, for 2 hours reduced the water content to 177 ppm. The processed oil was characterized following ASTM D6871 methods. This oil presented higher dielectric breakdown voltage (55 kV) than commercial transformer fluids (BIOTEMP®, EnvirotempFR3®, and Bivolt®), which increases transformer safety, capacity and lifetime. In addition, the processed oil has a lower viscosity than BIOTEMP® fluid, which can enhance the heat dissipation efficiency in the transformer. Moreover, the processed oil flash and fire points of 310°C and >340°C, respectively, confirm the great security of vegetable insulating fluids. The analyzed properties of the processed oil fulfill all the ASTM D6871, ABNT NBR 15422 and IEC 62770 specifications. Therefore, Jatropha curcas oil is a potential substitute formineral insulating fluids.

/pdf/development-of-a-new-bio-based-insulating-fluid-from-1q5es0yh2j.pdf

Development of a New Bio-Based Insulating Fluid from Jatropha curcas Oil for Power Transformers

The paper presents a comparison investigation to thermal aging behaviors between vegetable and mineral oil-paper insulation. Insulation pressboard samples were aged at 130 °C for 80 days in presence of either vegetable or mineral insulating oils, with copper wires together in well-sealed stainless vessels. The vessels contain some air in their vacant space at the beginning of the thermal aging experiments. The aged oil properties, including moisture content, acid number, viscosity, furfural concentration, dielectric loss, and AC breakdown voltage of oil samples, were measured at each interval of thermal aging experiment. The vegetable has a higher moisture content than mineral oil. Dielectric loss increases marginally with aging time in mineral oil while the increase is drastic for vegetable oil.

Comparison analysis to thermal aging properties of vegetable and mineral insulating oils

This article aims to contrastively study the thermal aging characters under different temperature between natural ester and mineral oil-pressboard insulation system. The thermal aging experiment was conducted with copper flat bars together in a sealed stainless vessel at 130 °C for 80 days, and at 100 °C for 220 days separately. Some basic physicochemical and electric characteristics of oil and cellulose varied with aging time, including moisture content, acid value, viscosity, furfural content, dielectric loss, AC breakdown voltage of oil, and the degree of polymerization were tested at each scheduled aging time. Results showed that the value of moisture content and dielectric loss in natural ester were higher than that of mineral oil, but it had a better insulation strength and service life.

Jinhui Zhou

Papers

Comparison analysis to thermal aging properties of vegetable and mineral insulating oils

Thermal aging properties of pressboard in mineral oil and natural ester