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Authors = Eleftheria C. Pyrgioti

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17 pages, 5415 KiB  
Article
Breakdown Performance and Partial Discharge Development in Transformer Oil-Based Metal Carbide Nanofluids
by Konstantinos N. Koutras, Sokratis N. Tegopoulos, Vasilios P. Charalampakos, Apostolos Kyritsis, Ioannis F. Gonos and Eleftheria C. Pyrgioti
Nanomaterials 2022, 12(2), 269; https://doi.org/10.3390/nano12020269 - 14 Jan 2022
Cited by 40 | Viewed by 3828
Abstract
In this work, the influence of semi-conductive SiC nanoparticles on the AC breakdown voltage and partial discharge development in natural ester oil FR3 is examined. Primarily, the dielectric constant and the electrical conductivity of the nanoparticles are measured following the broadband dielectric spectroscopy [...] Read more.
In this work, the influence of semi-conductive SiC nanoparticles on the AC breakdown voltage and partial discharge development in natural ester oil FR3 is examined. Primarily, the dielectric constant and the electrical conductivity of the nanoparticles are measured following the broadband dielectric spectroscopy technique. The nanoparticles are added into the matrix following the ultrasonication process in three weight percentage ratios in order for their effect to be evaluated as a function of their concentration inside the base oil. The processing of the results reveals that the nanofluid containing SiC nanoparticles at 0.004% w/w demonstrates the highest AC dielectric strength improvement and shows the greatest resistance to the appearance of partial discharge activity. The mechanisms behind the aforementioned results are discussed in detail and confirmed by the broadband dielectric spectroscopy technique, which reveals that this particular nanofluid sample is characterized by lower dielectric constant and electrical conductivity than the one with double the weight percentage ratio. Full article
(This article belongs to the Special Issue New Frontiers in Nanofluids)
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16 pages, 3068 KiB  
Article
The Influence of Nanoparticles’ Conductivity and Charging on Dielectric Properties of Ester Oil Based Nanofluid
by Konstantinos N. Koutras, Ioannis A. Naxakis, Eleftheria C. Pyrgioti, Vasilios P. Charalampakos, Ioannis F. Gonos, Aspasia E. Antonelou and Spyros N. Yannopoulos
Energies 2020, 13(24), 6540; https://doi.org/10.3390/en13246540 - 11 Dec 2020
Cited by 24 | Viewed by 3230
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. [...] Read more.
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. Full article
(This article belongs to the Topic Applications of Nanomaterials in Energy Systems)
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11 pages, 2280 KiB  
Article
Dielectric Insulation Characteristics of Natural Ester Fluid Modified by Colloidal Iron Oxide Ions and Silica Nanoparticles
by Vasilios P. Charalampakos, Georgios D. Peppas, Eleftheria C. Pyrgioti, Aristides Bakandritsos, Aikaterini D. Polykrati and Ioannis F. Gonos
Energies 2019, 12(17), 3259; https://doi.org/10.3390/en12173259 - 23 Aug 2019
Cited by 26 | Viewed by 3685
Abstract
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 [...] Read more.
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. Full article
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