A comparison of breakdown properties of natural and synthetic esters at high voltage

Abstract

Ester-based insulating liquids are considered today for electrical insulation in medium and high voltage transformers. The main advantages expected are their non-toxicity, excellent biodegradability, and fire resistance. Esters can be either of natural origin or synthetic. In this work, we present a study of prebreakdown and breakdown properties at high voltage and large gaps in several natural and synthetic esters, and a comparison with the well-know mineral transformer oil. This study is focused on the study of streamer propagation in large gaps up to 10cm. Compared to mineral oil, the transition to fast streamers in esters occurs at much lower voltage. Measurements also show no difference between esters, whatever their origin, viscosity, etc. From these results, it appears that the properties of esters are less favorable for very high voltage insulation than in mineral oil: once triggered, streamers are able to propagate very quickly to breakdown at lower voltage. In consequence, esters show a lower resistance to fast transients such as the standard lightning impulse.

The effect of polarity on the lightning breakdown voltages of palm oil and coconut oil under a non-uniform field for transformers application

“…Furthermore, it is observed that the content of saturated and unsaturated fats have no significant effect on the lightning breakdown performances since most of the breakdown voltages of all RBDPO are quite close to CO. The relationship between RBDPO/CO and gap distance is found to be following the same pattern as previous studies in MO and other types of esters (Liu et al, 2009;Ngoc et al, 2010;Liu and Wang, 2011;Wang et al, 2011;Wang et al, 2012). As part of the practical application, a model that could describe the relationship between RBDPO/CO at wide range of gap distance is needed which is important at design stage of transformers.…”

“…Under negative polarity, the highly mobility electrons cause smaller contribution of the space charge and higher negative applied voltages are needed for an event of breakdown to occur (Schmidt and Pugh, 1977). For esters, the differences between positive and negative breakdown voltages are lower than MO (Duy et al, 2009, Rongsheng et al, 2009Ngoc et al, 2010;Wang et al, 2011). In other study, it was observed that the differences between breakdown voltages of MO and esters between negative and positive polarities increased as the gap distance increased (Forster et al, 1994).…”

Study of Dielectric Properties of a Potential RBD Palm Oil and RBD Soybean Oil Mixture as Insulating Liquid in Transformer

“…14. Dissipation factor of 10%, 30% and 50% of RBDPO content at 40°C, 70°C and 90°C compared with mineral oil [9] and IEC 60296 standard dissipation factor of the RBDPO/RBDSO mixture has shown descending trend from 10% to 50% RBDSO ratio. This result shows that the addition of 0% to 50% RBDSO into RBDPO gives a positive effect on the dissipation factor.…”

“…10. Dielectric strength of RBDPO/RBDSO mixture dependence on RBDSO content compared with mineral oil [9] and IEC 60296 standard…”

“…Moreover, in the last five years, numerous researches pertaining to the uses of natural ester as an insulating liquid in electrical power transformer had been extensively conducted either singly or in combination with mineral oil [8][9][10][11][12][13][14][15][16][17]. The selection is due to its compatible dielectric properties which best suit its function as an insulating liquid, fire safety advantageous and most importantly it is renewable and environmentally friendly product.…”