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Energies 2017, 10(4), 511; doi:10.3390/en10040511

Comparative Study of Breakdown Voltage of Mineral, Synthetic and Natural Oils and Based Mineral Oil Mixtures under AC and DC Voltages

1
Ecole Centrale de Lyon, University of Lyon, Ampere CNRS UMR 5005, 36 avenue Guy Collongue, 69134 Ecully, France
2
Electrical Engineering Department, College of Engineering, King Saud University, Riyadh 11421, Saudi Arabia
3
Electrical Engineering Department, Faculty of Energy Engineering, Aswan University, Aswan 81528, Egypt
4
Electrical Engineering Department, Engineering Faculty, Universitas Lampung (Unila), Bandar Lampung, Lampung 35141, Indonesia
*
Author to whom correspondence should be addressed.
Academic Editor: Pierre Trambouze
Received: 27 February 2017 / Revised: 23 March 2017 / Accepted: 23 March 2017 / Published: 10 April 2017
(This article belongs to the Section Electrical Power and Energy System)

Abstract

This paper deals with a comparative study of AC and DC breakdown voltages of based mineral oil mixtures with natural and synthetic esters mainly used in high voltage power transformers. The goal was to analyze the performances of oil mixtures from the dielectric withstand point of view and to predict the behavior of transformers originally filled with mineral oil and re-filled with synthetic or natural ester oils when emptied for maintenance. The study concerns mixtures based on 20%, 50%, and 80% of natural and synthetic ester oils. AC breakdown voltages were measured using a sphere-sphere electrode system according to IEC 60156 specifications; the same specification was adopted for DC measurements since there is no standard specifications for this voltage waveform. A statistical analysis of the mean values, standard deviations, and histograms of breakdown voltage data was carried out. The Normal and Weibull distribution functions were used to analyze the experimental data and the best function that the data followed was used to estimate the breakdown voltage with risk of 1%, 10%, and 50% probability. It was shown that whatever the applied voltage waveforms, ester oils always have a significantly higher breakdown voltage than mineral oil. The addition of only 20% of natural or synthetic ester oil was sufficient to considerably increase the breakdown voltage of mineral oil. The dielectric strength of such a mixture is much higher than that of mineral oil alone and can reach that of ester oils. From the point of view of dielectric strength, the mixtures constitute an option for improving the performance of mineral oil. Thus, re-filling of transformers containing up to 20% mineral oil residues with ester oils, does not present any problem; it is even advantageous when considering only the breakdown voltage. Under AC, the mixtures with natural ester always follow the behavior of vegetable oil alone. With the exception of the 20% mixture of natural ester in DC, the breakdown voltage values of all the tested mixtures were in accordance with the normal distribution, which made it possible to define the breakdown voltages for the risk levels of 1%, 10%, and 50% of probability. View Full-Text
Keywords: insulating oils; vegetable oil; synthetic oil; mineral oil; oil mixtures; AC breakdown voltage; DC breakdown voltage; re-filling of power transformers; statistical analysis; normal distribution; Weibull distribution insulating oils; vegetable oil; synthetic oil; mineral oil; oil mixtures; AC breakdown voltage; DC breakdown voltage; re-filling of power transformers; statistical analysis; normal distribution; Weibull distribution
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Beroual, A.; Khaled, U.; Mbolo Noah, P.S.; Sitorus, H. Comparative Study of Breakdown Voltage of Mineral, Synthetic and Natural Oils and Based Mineral Oil Mixtures under AC and DC Voltages. Energies 2017, 10, 511.

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