The Influence of Nanoparticles’ Conductivity and Charging on Dielectric Properties of Ester Oil Based Nanofluid

Konstantinos N Koutras,Eleftheria C Pyrgioti,Spyros N Yannopoulos,Aspasia E Antonelou,Ioannis F Gonos,Vasilios P Charalampakos,Ioannis A Naxakis

doi:10.3390/en13246540

Abstract

This study addresses the effect of nanoparticles’ conductivity and surface charge on the dielectric performance of insulating nanofluids. Dispersions of alumina and silicon carbide nanoparticles of similar size (~50 nm) and concentration (0.004% w/w) were prepared in natural ester oil. The stability of the dispersions was explored by dynamic light scattering. AC, positive and negative lightning impulse breakdown voltage, as well as partial discharge inception voltage of the nanofluid samples were measured and compared with the respective properties of the base oil. The obtained results indicate that the addition of SiC nanoparticles can lead to an increase in AC breakdown voltage and also enhance the resistance of the liquid to the appearance of partial discharge. On the other hand, the induction of positive charge from the Al2O3 nanoparticles could be the main factor leading to an improved positive Lightning Impulse Breakdown Voltage and worse performance at negative polarity.

Highlights

The lifetime of the power transformer is a major factor for the reliability and uninterrupted operation of the electricity grid
Dielectric strength for a gap of 2.5 mm is 24.9 kV·mm−1, 25.9 kV·mm−1, and 28.9 kV·mm−1 for base, iNF, and sNF samples, respectively. This finding could be attributed to the fact that the addition of semi-conducting SiC NPs for the selected weight fraction can lead to the delay of streamer propagation, by trapping and de-trapping the fast electrons at the tip of the streamer in shallow traps [27,28,32,38]
If considerable divergence exists in conductivity or permittivity between NP and base oil, induced or polarized charges are generated at the interface between NP and matrix

Summary

Introduction

The lifetime of the power transformer is a major factor for the reliability and uninterrupted operation of the electricity grid. As well as the paper immersed in dielectric liquid, should provide protection of its windings under the influence of electrical, thermal, and even environmental effects to prevent short circuits and leakage currents [1,2]. The first step towards the improvement of transformer insulation is to turn the attention of research to the study of alternatives, such as natural or synthetic ester oils [7,8,9,10]. The use of ester oils entails, beyond improved properties like biodegradability and higher moisture tolerance, benefits for the transformer itself, essentially aging characteristics, enhanced lifetime, and loading capability [3,11,12].

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Results

Discussion

Conclusion