Natural Ester Fluid Research Articles

Rheological Analysis of Thermally Aged Natural Ester Fluid Using Nonlinear Least Square Technique

Rheological Analysis of Thermally Aged Natural Ester Fluid Using Nonlinear Least Square Technique

Application of Transformer Oil and Biodegradable Ester Mixtures as Insulation for High-Voltage Equipment

Synthetic and natural esters as insulating fluids for high voltage equipment have been a focus of much research, especially in the last two decades. This is due to the fact that, unlike mineral oil, ester fluids are biodegradable, non-toxic, safe for the environment and human health, produced from renewable raw materials, and feature high fire resistance. Despite the fact that commercially available ester fluids having excellent insulating properties are offered in the market, both transformer manufacturers and operators are not yet ready for mass-scale transition to the use of biodegradable ester dielectric fluids. In addition, since there is a huge amount of electrical equipment filled with mineral oil, mass-scale replacement of this oil with ester dielectric fluids will be extremely expensive for power companies. A suitable way for making a shift from oil to esters can be partial replacement of mineral oil with ester fluids (for example, topping up during repairs) or complete replacement of mineral oil with biodegradable esters. Whatever of these options is implemented, there will be a mixture of two insulating fluids inside of the equipment. Therefore, specialists intensely study the characteristics and behavior of insulating mixtures based on mineral oil and other dielectric fluid (synthetic ester, natural ester or silicone fluid). The article presents a review of the latest advances in the investigations of mixtures consisting of mineral oil and other dielectric fluids, including the studies of their properties. Problems associated with the operation of equipment in the case of its filling with mixed liquids are discussed.

Enhancement of characteristics of ester based insulating oil in the presence of nano composites

The development of reliable, environmentally safe and economically viable insulating oil for transformers is an endless effort of the electrical industry. Recent research is based on natural ester fluid, a green insulating oil that exhibits excellent dielectric performance and environment friendly characteristics. Mineral oil is a popular dielectric liquid used in transformers and switchgear. The environmental hazards caused by the oil have reached an alarming level and several incidents relating to transformer explosions have been reported worldwide, one major cause being the insulation failure. The requirement of an insulating liquid with fire safety and biodegradable nature has become a key concern of transformer manufacturers. One such kind of oil is Refined Coconut Oil having similar properties and characteristics as mineral oil. Refined coconut oil is commonly available as an environmentally friendly ester oil. In the present work, nano- fluids such as Nano MgO and nano BN have been added in different concentrations to identify their positive effects on improvement in the characteristics of mineral oil. It is also conclusively proved that nano-fluids are potential replacements for mineral oil since the qualities of the base oil were improved by the inclusion of nanoparticles.

Development of Eco-Friendly Transformer Oil from Neem Seed Oil using Periwinkle Waste Shell as Catalyst

Abstract The urge for a sustainable and non-polluting industry has raised the need for a search for an alternative insulating fluid that could be used in transformers, because of the negative environmental effect of mineral-based insulating fluids. Natural esters from non-edible oil seeds showed to be feasible alternative, unfortunately they possess poor thermooxidative properties. Neem trees grow nearly on all types of soils and can be as old as 45 years before they start to produce less fruits. Neem tree can produce up to 50 kg of its fruits yearly from the tenth year and the seed oil content is 45 % making it a sustainable tree. The neem seed transformer oil (NSTO) was produced via catalysed transesterification process using neem seed oil and methanol with periwinkle shell as catalyst. Prior to the transesterification reaction the seed oil was degummed. The produced ester also underwent water treatment process. The produced NSTO density, water content, acidity flash point, pour point, viscosity, breakdown voltage, dielectric, relative dielectric constant, dissipation factor and resistivity properties were tested, presented and discussed. Results show that NSTO meet most of the standard requirements of new natural ester fluids as insulating oil. The dielectric breakdown voltage of the oil is 32 kV, which is more than the required for new natural ester fluids. The dissipation factor limit value for new natural ester of 0.20 % at 25 °C limit value was met by NSTO from 100 Hz to 400 Hz, and the relative dielectric constants of NSTO are 3.01 k, which value also meets the specification of between 2.9 k and 3.2 k. The pre-treatment of degumming of the seed oil prior to transesterification and water treatment of the produced ester appears to be a promising route for the production of electrical insulating oil for transformer.

Mobility of charge carriers in mineral oil and ester fluids

New, more stringent environmental requirements for electrical insulation liquids have led to the development of novel, more environment-friendly liquid dielectrics. Ester fluids, introduced several decades ago, provide a viable alternative to traditional mineral insulating liquids. In order to expand the practical applications of these novel dielectric fluids, their dielectric and electrical parameters should be established. One of the critical parameters that affects and governs the development of pre-breakdown processes in insulating liquids is the mobility of charge carriers. In the present paper, the mobility of charge carriers in commercially available synthetic and natural insulating ester fluids and in a mineral insulating oil were obtained using two methods, the time of flight and the space charge saturation current methods. The mobility was obtained for a wide range of electrical field magnitudes. It was found that the mobility of charge carriers is greater in the mineral oil than in both, the natural and synthetic, ester fluids. It was also established that the mobility is higher for higher applied electric field. The results of this work will help in characterizing liquid dielectrics and in optimizing high-voltage systems in which liquid dielectrics, including natural and synthetic ester fluids, are used.

Temperature dependence of the pre-breakdown and breakdown phenomena in natural esters under AC stress

Natural ester dielectric fluids are being used as alternatives for mineral insulating oils in oil-filled power apparatuses. Although partial discharges (PDs) are recognised as one of the main causes of degradation of dielectrics used in power equipment, their characteristic voltages appear to be temperature-dependent. In this contribution, the pre-breakdown and breakdown behaviour of two natural ester fluids, extracted from canola oil (NE1) and soybean oil (NE2) is reported. To assess the effectiveness of the temperature dependence, −5, 0, and + 20°C have been identified as test temperatures. It was found that the different pre-breakdown and breakdown characteristic voltages increase with increasing temperature for both types of esters. The delay time is always longer for canola oil when compared to soybean oil regardless of the test temperature. The analysis of the average propagation velocity of NE1 and NE2 indicates that PDs propagate faster in NE2 than in NE1. The field strength at the tip of the needle electrode during the inception of the streamers leading to breakdown indicates that streamers in both oils are propagating in the slow mode. It is found that the temperature has a significant influence on the PDs’ parameters for both fluids.

Investigation on the performance of thermally aged natural ester fluid impregnated pressboard material

This paper reports the key findings from an experimental study carried out on thermally aged natural ester fluid impregnated pressboard (EOIP) material. The results show that the surface discharge inception voltage (SDIV) with thermally aged EOIP material is higher under negative DC voltage compared with positive DC and AC voltage. The SDIV increases with AC voltage frequency and a minimal reduction in voltage was observed under harmonic AC voltages with different total harmonic distortion (THD). The rate of change in voltage due to ripple content in DC voltage affects the SDIV of EOIP material, initiating discharges at lower voltages. The UHF signals radiated during the surface discharge process have a bandwidth in the range 0.9 to 2 GHz. Surface potential variation studies indicated the formation of high trap sites and trap density due to thermal aging. A reduction in the oxidation onset temperature and the activation energy of thermal decomposition were observed with thermally aged EOIP material. A pyrolysis study showed high composition of levoglucosan and acidic residue with the thermally aged specimen, which reduces its degree of polymerization. Impedance spectroscopic analysis indicates a non-Debye type of relaxation with thermally aged EOIP material. The mobility and charge transfer characteristics were also inferred from the modulus spectroscopy which showed less change for thermally aged pressboard material.

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

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.

Dielectric Insulation Characteristics of Natural Ester Fluid Modified by Colloidal Iron Oxide Ions and Silica Nanoparticles

In this study, the dielectric characteristics of two types of natural esters modified into nanofluids are studied. The AC breakdown voltage was investigated for colloidal Fe2O3 and SiO2 nanoparticles effectively scattered in natural ester oil. The experimental results identify an increase in the breakdown voltage of the nanofluid with colloidal Fe2O3 conductive nanoparticles. In contrast, the breakdown voltage was reduced by adding SiO2 nanoparticles in the same matrix. The potential well distribution of the two different types of nanoparticles was also calculated in order for the results of the experiment to be explained. The dielectric losses of the colloidal nanofluid are compared with the matrix oil and studied at 25 °C and 100 °C in the frequency regime of 10−1–106 Hz. The experimental data and the theoretical study reveal that conductivity along with the permittivity of nanoparticles constitute a pivotal parameter in the performance of nanofluid. Specific concentrations of nanoparticles with different electrical conductivity and permittivity than those of matrix oil increase the breakdown voltage strength. Simultaneously, the addition of nanoparticles having electrical conductivity and permittivity comparable to the matrix oil results in reducing the breakdown voltage.

Fire resistance test of transformers filled with natural ester insulating liquid

Natural ester fluids, as a renewable, biodegradable liquid dielectric, its flash point is above 300°C, and the burning point exceeds 330°C, high flash point liquids known as ‘less flammable’ liquids. There is a possibility applying the natural ester fluid immersed transformer instead of dry type transformer in high fire resistance requirement occasion. In order to verify the fire resistance of natural ester insulating oil transformer, set forth a series of contrast test between natural ester insulating oil and mineral insulating oil, including flash point, burning point, explosion limits, metal hot surface test, and burning plate test. Through developing burning test platform of transformer to launch the burning test for 10 kV transformer of natural ester insulating oil. The results show that the transformer filled with natural ester fluid cannot burn for 30 min in the case of severe external fire, which provides a relatively abundant time for fire extinguishing and has certain fireproof performance. In addition, by improving the mechanical strength of transformer tank, install the specific pressure relief devices and using high temperature seal, bushing etc., which can improve the fire resistance of transformers filled with natural ester insulating fluids.

Electro-convection in natural ester based transformer fluid

The electro-convection phenomenon is among the pre-breakdown phenomena influencing the dielectric strength of insulating fluids. In transformer mineral oils, electro-convection can lead to catastrophic failure of transformers. With the current trend to replace mineral oils with natural ester fluids, it is important to characterize this phenomenon in vegetable fluids. This paper deals with the influence of different parameters on the electro-convection phenomenon in natural ester fluid; mineral oil is also considered for comparison. The investigations concern especially the dependence of the electro-convection threshold voltage of the electric field distribution, electrodes spacing distance, electrode material, water content in oil and temperature. The electro-convection threshold voltage in natural ester fluid is also compared to that in mineral oil. It is shown that the electro-convection threshold voltage is the lowest with electrodes made of copper and the highest for those made of aluminum; it is in between for electrodes made of brass. Also, the electro-convection threshold voltage is smaller in natural ester fluid than in mineral oil; the influence of water content is weaker in natural ester fluid.

Identification of Critical Values Based on Natural Ester Oils as Potential Insulating Liquid for High Voltage Power Transformers

This study tries to bring a complex summary of properties of natural ester fluids from the point of view of electrical insulation fluid for high voltage power transformers. Although many papers have been published in this area , this study try to address some less known problems which however plays a key role in new fluid practical applications. S ome differences compared to mineral oils are discussed in study. The critical values that might occur in the future for industrial applications are proposed, evaluated and discussed.

Transformadores de distribución que operan con aceite de origen vegetal como dieléctrico y refrigerante

Researches related with the use of Natural Ester Fluids as refrigerant of power transformers have been developed in other countries with successful results. In Colombia there is no a procedure to control the use of these esters in electrical apparatus, so the current implementations are regulated by NTC 1465 standards for mineral esters. This new proposal involves the composition and the most relevant properties (the ignition resistance, impact on the lifetime of the insulating papers and the impact on the environment), which makes the application of natural esters fluids advantageous not only to preserve the environment but also to get a better performance of power transformers.

Pre-breakdown phenomena in new vegetable oil - based jatropha curcas seeds as substitute of mineral oil in high voltage equipment

Due to their high biodegradability, non-toxicity and higher fire safety guarantee, vegetablebased oils are considered today as a potential substitute for mineral and synthetic liquids for electrical insulation and especially in high voltage power transformers. However most of known vegetable oils are derived from food materials (rape-seeds, sunflower, soybeans, palms, corns and others). And one has to be vigilant to the fact that the replacement of mineral oil by natural ester fluids based on “renewably sourced” vegetable oils, does not create new problems as this could cause global food crisis due to diversion of food into insulating material oils or others (fuel). An interesting product can be jatropha curcas oil (JCO) extracted from the fruit seeds of jatropha curcas plants (“miracle tree”) which is non-food crops. These plants can be grown on marginal or degraded soils and thus enables to avoid the need to utilize those more fertile soils currently being used by smallholders to grow their staple crops; and they readily grow in areas where annual rainfall levels are significantly lower than those required by other species such as rape-seeds, sunflower, palm, soybeans, corns and others. This paper presents an experimental study of streamers phenomena in jatropha curcas methyl ester oil (JMEO) and mineral oil (MO) under positive and negative lightning impulse voltages (1.2/50 μs); JMEO is obtained by alkali base catalyzed trans-esterification process of JCO to reduce the viscosity and acidity. It is shown that basing on the streamer characteristics (shape, stopping length, velocity, current and electrical charge), JMEO could constitute a potential substitute for mineral for electrical insulation and especially in high voltage power transformers.

Comparative studies of the stability of various fluids under electrical discharge and thermal stresses

It is a well-known fact that the service reliability of power transformers largely depends upon the condition of the dielectric fluid. The steady deterioration (under the influence of the multiple stresses) of the insulation has an important impact on the condition of the transformers themselves. This contribution reports some investigations on some commercially available ester, silicone and mineral oil fluids. Some of their physicochemical properties are studied by submitting them to various stresses: electrical, thermal and oxidation. Many comparisons are made according to the quality test results of mineral oil, as it is very familiar to the transformer industry. A new technique using a reactive free radical reagent, 2,2-diphenyl-1- picrylhydrazyl (DPPH), added to both new oil for reference purposes and different aged oil to assess free radical concentration is presented. The gassing tendency under either thermal or electrical stress, along with the physicochemical properties of the fluids, is affected; it is assessed with the production of oxidative aging by-products. The gassing performance characteristics of natural ester fluids are far superior to those of conventional mineral oil. A significant reduction in insulation aging rate was observed with synthetic ester fluids.

Cold Start of a 240-MVA Generator Step-Up Transformer Filled With Natural Ester Fluid

A 240-MVA, 165-GRDY/20-kV generator step-up transformer was insulated with Envirotemp FR3 fluid. The transformer was energized during a cold temperature period in mid-December 2010. This is believed to be the largest generator step-up transformer filled with a natural ester fluid that was energized at low temperatures. The lack of cold start experience of natural ester-filled power transformers created questions and at least some uncertainty as to the outcome. This paper describes the instrumentation used and data collected during the cold startup procedure. In addition, a computational fluid dynamics analysis of this transformer design was performed that provided calculated temperatures and elapsed times until steady-state temperatures were achieved. Comparisons were made between the actual and calculated values. The results indicate that the cold startup procedures for a power transformer are the same whether filled with mineral oil or natural ester fluid of similar characteristics as used for this paper.

Analysis of partial discharge characteristics of natural esters as dielectric fluid for electric power apparatus applications

Petroleum based mineral oils are generally used for electric power apparatus insulation and cooling applications. Since the conventionally used mineral oils are not biodegradable and difficult to decompose, there is a need for the development of alternate vegetable based insulation oils for such applications. Formation of partial discharges plays a major role in determining the life time of liquid insulation. Reports on partial discharge characteristics of thermal aged natural ester fluids for high voltage applications are scanty. The major aim of this research work is to understand the partial discharge characteristics of natural esters as a dielectric fluid for power transformer and other electric power apparatus insulation applications. Laboratory experiments are performed as per IEC (International Electro technical Commission) test procedures in order to understand the breakdown voltage and partial discharge characteristics of vegetable oils such as corn oil and palm oil under both virgin and thermal aged conditions. This paper presents a comparative assessment of the PD characteristics of thermal aged natural ester fluids with respect to mineral oil. Time and frequency domain analysis of PD pulse at both needle-plane and rod-plane electrode configurations are studied. Statistical analysis of PD pattern is also carried out. This analysis collects the typical PD patterns from natural ester fluids in order to find its suitability for power transformer and electric power apparatus applications.

Reducing Environmental Impact and Improving Safety and Performance of Power Transformers With Natural Ester Dielectric Insulating Fluids

Natural ester fluids may be used in new transformers as well as to retrofill existing units in order to improve their performance and reliability. Designing or retrofilling power transformers with natural ester fluids requires, however, to account for a number of significant differences in properties, characteristics, and material parameters between natural ester fluids and mineral oil in order to obtain the desired performance (thermally and dielectrically). This paper gives a comprehensive review of natural-ester-fluid main properties and associated values when it comes to environmental impact, fire resistance, and overall performance of transformers filled with such fluids. The key fluid characteristics impacting the design of power transformers are also highlighted.

The Lightning Impulse Properties and Breakdown Voltage of Natural Ester Fluids Near the Pour Point

Recently, researchers have become interested in natural ester fluids, as they are an environmentally friendly alternative to mineral oils. Natural ester fluids are a natural resource made from plants; they have higher biodegradability, flash, and fire points, and a greater permittivity compared to conventional mineral oils. However, natural ester fluids also have a higher pour point, viscosity, and water content. These characteristics can hamper circulation and impair the electrical properties of an oil-filled transformer. A large amount of data has been accumulated over the years in regards to mineral insulating oil involving dielectric breakdown voltage and lightning impulse tests. However, natural ester fluids have not had their electrical properties sufficiently characterized. In this paper, we present an investigation into the characteristics of the electrical discharge development in natural ester fluids and in an oil-filled transformer near the pour points. The experiment results show that the electrical properties decreased according to a decrease in the ambient temperature and freezing time. It was found that the pour point and water content of natural ester fluids have a significant effect on the electrical properties.

Insulating properties and charge characteristics of natural ester fluid modified by TiO2 semiconductive nanoparticles

In order to improve dielectric performance of natural esters, TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> semiconductive nanoparticles were added to obtain an ester-based nanofluid. AC, lightning impulse voltage and partial discharge tests were applied to the natural ester and the ester-based nanofluid to check their dielectric performances. It was found that TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles can not only enhance AC breakdown voltage of the ester based nanofluid by a factor of 1.3 but also improve the partial discharge properties of the ester based nanofluid compared to that of the natural ester. Pulse electroacoustic (PEA) and thermally stimulated current (TSC) techniques were applied to investigate charge transport and trap characteristic in natural ester and ester-based nanofluid. It reveals that TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles can accelerate the charge dissipation rate and uniform the electric field and increase the shallow trap density in the ester-based nanofluid. It is proposed that electron trapping and de-trapping processes in the shallow traps could be one of the main charge transport processes in the ester based nanofluid.