Nanofluids, formed by adding nanoscale particles to insulating oil, are stable and homogeneous suspensions that present advanced performance of electrical insulation and heat dissipation. This study shows a comprehensive literature review based on the related results of nano-modified insulating oils (both mineral and vegetable insulating oils) to analyse the preparation methods, stability, dielectric spectroscopy, thermal conductivity, breakdown characteristics under AC and DC voltage, the thermal aging performance of nanofluids and oil-paper interaction. Then theoretical models have been introduced to explain the electrical mechanism of nanofluids. In addition, future research is proposed for nanofluids which would be low cost, highly stable and practically applicable to the power transformers.

Electrical and thermal properties of insulating oil-based nanofluids: a comprehensive overview

Recently, nanofluids are introduced in the power utilities for the dielectric performance enhancement of power transformer oil. The compactness and fault improvement of the power transformers has resulted in the necessity of next-generation insulating fluid with inflated dielectric properties. This article investigates the dielectric performance of the novel ester oil-based magnetic nanofluids with different nanoparticles under different electric stress conditions. Two biodegradable fluids used as the base liquid for the experiment are synthetic ester oil and natural ester oil while three magnetic nanoparticles used to synthesize nanofluids are iron (II, III) oxide, cobalt (II, III) oxide, and iron phosphide. The concentrations of the nanoparticles are varied to optimize the characteristics of the prepared nanofluids. The dielectric breakdown and relative permittivity of the nanofluids have been experimentally investigated. Further, the breakdown predictions have been performed using Weibull statistical distribution-based regression analysis. The experimental results show the improvement in the characteristics of prepared nanofluids with the change in nanoparticle concentration as compared with the host fluids.

/pdf/dielectric-performance-of-magneto-nanofluids-for-advancing-4oq4t6skt8.pdf

Dielectric Performance of Magneto-Nanofluids for Advancing Oil-Immersed Power Transformer

The use of dielectric nanofluids has been recently proposed as a method to improve the insulation system of transformers. It has been widely reported that these liquids present superior dielectric properties than conventional dielectric liquids and have a better behavior as cooling agents. Nevertheless some aspects need to be addressed before these materials are applicable to real equipment. This paper analyzes the interaction between dielectric nanofluids and the cellulose materials that constitute the solid insulation of transformers. The impregnation process of a transformer has been emulated in order to obtain samples of solid insulation impregnated with a 
$$\hbox {Fe}_{3}\hbox {O}_{4}$$

 based nanofluid. The samples have been subjected to ICP testing and Cryo-SEM observation, complemented with the determination of the EDX sprectrum. The interaction between the nanoparticles and the cellulose fibers has been investigated finding that bonds are established between them when cellulose is impregnated with nanofluids.

/pdf/morphological-analysis-of-transformer-kraft-paper-11m2g9u8m5.pdf

Morphological analysis of transformer Kraft paper impregnated with dielectric nanofluids

Mobile communication systems are undoubtedly an environmental source of electromagnetic radiation (EMR). Although the direct health effect of a cell phone to human is still elusive, the effect to unicellular organisms is rather apparent. The aim of this study was to examine the effects of EMR on development of bacterial biofilm. Microtitration plates with four strains of Staphylococcus aureus were exposed to electromagnetic field of frequencies 1-5 GHz, which are used in mobile phones. The results showed mostly the inhibition of the development biofilm activity at frequencies 1, 2 and 3 GHz, however the significant stimulation of biofilm development occurred at frequencies 4 and 5 GHz. Our observations demonstrate that EMR exposure produced modulation effects on bacterial biofilms, which are very important in commensal and pathogen bacteria.

Modulation of staphylococcus aureus biofilm by electromagnetic radiation

The interest in developing and testing dielectric nanofluids for electrotechnical purposes has increased significantly in the last ten years. A number of works have been published reporting dielectric and thermal properties for these liquids that enhance those of conventional insulating fluids. Some authors propose that the application of dielectric nanofluids to transformer insulation could improve the reliability of transformers and open new possibilities for transformer design. However, this will not be feasible until thorough studies on the interaction of these materials with other elements of the transformer, specially the solid insulation, are carried out. In this work, the effect of the presence of nanoparticles on the dielectric response of oil and oil-paper insulation is analysed in laboratory conditions. Specimens have been prepared to emulate the insulation system of transformers and the dielectric response in the frequency domain of these specimens has been characterized. The dependence of nanoparticle concentration on the dielectric response has been analysed. Proposing physical mechanisms that explain the experimental results observed over the oil and the paper samples. Some conclusions are extracted in this work that may be of interest if nanofluids are considered as liquid insulation for transformers.

/pdf/dielectric-response-of-the-oil-paper-insulation-system-in-2tujureqmu.pdf

Dielectric Response of the Oil-Paper Insulation System in Nanofluid-Based Transformers

This paper deals with the measurement and comparison of the current characteristics of the liquid dielectric in the frequency and time domains. The theoretical part contains properties of insulating materials, a description of the impedance spectroscopy method in the frequency domain and IRC analysis. The practical part contains experimental description, used sample of liquid dielectric and analysis of measured results with graphical representation of capacity values and loss factor on frequency and values of charging current over time.

Impedance Spectroscopy of Liquid Insulating Materials

In this paper, the thermal ageing of pressboard impregnated with two kinds of insulation liquids is studied by means of frequency domain spectroscopy which involves the measurement of real and imaginary part of complex permittivity as function of frequency. The magnetic nanofluid was composed by mineral transformer oil as carrier liquid, nanoparticles of magnetite and surfactant. The thermal aging test was performed at the temperature 90°C for 1000 hours. Each sample had two variations, with and without copper, which has function catalyst. Then frequency domain spectroscopy was investigated at 40°C for restriction of moisture influence from surrounding. From the data and curves, it can be shown that the undried samples are dried with the aging time and cooper considerably getting worse the imaginary part of complex permittivity. In case of magnetic nanofluid, the colloidal suspension was unstable after 800 hours of the thermal ageing. There was found much more resistance of moisture at the nanofluids than in case of mineral oil impregnated pressboard.

Thermal degradation of transformer pressboard impregnated with magnetic nanofluid based on transformer oil

This paper deals with the negative abrasive effect of magnetic nanofluids on paper insulation. Nanofluid with magnetite Fe3O4 nanoparticles and conventional transformer paper was used in the experimental part. The simple degradation device based on magnetic properties of nanofluid for the simulation of fluid flow was constructed. Frequency dependent spectroscopy in 20 Hz - 2 MHz domain for analysis of results was used. Moreover, the analysis of samples under the microscope was additionally carried for detection of paper insulation disruption. The microscopic images were processed in 8-bits scale of grey and analysed by a software tool. The results of the experiment indicate the possible negative effect of nanoparticles on cellulose fibres.

Abrasive properties of transformer oil-based magnetic nanofluid

This paper deals with evaluation of shielding effectiveness by measurement in anechoic chamber for combination of shielding paint with building materials. The material used for the experiment was polystyrene POLYFORM with thickness 5 cm, shielding paint YSHIELD HSF 64, water and building glue BauKleber, class C1T. The measurement was performed in the frequency range from 1 GHz to 9 GHz with step 50 MHz

Influence of shielding paint on the combination of building materials for evaulation of shielding effectiveness

The article deals about magnetic fluids based on a transformer ITO100 oil and about behaviour of these fluids under influence of permanent magnetic field represented by time-current characteristics. The measurements were performed in an anechoic EMC chamber and outside the chamber for comparing the results on the same samples. The main objective was to determine how much is the measurement influenced by external electromagnetic fields that generate around electrical equipment and the impact of higher harmonics in the power supply voltage. The measurement is dependent from orientation of actuating magnetic field, this behaviour mainly shows the effect of nanoparticles structuring during exposition of specimen by magnetic field. These particles also changes polarization processes in fluid influence of nanoparticles concentration contained in the fluid.

Lukas Kruzelak

Papers

Impedance Spectroscopy of Liquid Insulating Materials

Thermal degradation of transformer pressboard impregnated with magnetic nanofluid based on transformer oil

Abrasive properties of transformer oil-based magnetic nanofluid

Influence of shielding paint on the combination of building materials for evaulation of shielding effectiveness

Influence of electromagnetic interference on time-domain spectroscopy of magnetic nanofluids