Synthetic esters have become more and more popular in last few decades, explaining the increasing number of units filled with this liquid year by year. They have been investigated under different aspects, both from the fundamental point of view and breakdown mechanisms, well as from the application point of view. However, their use in high voltage equipment is always a challenge and deeper knowledge of the various aspects that can be encountered in their exploitation is needed. The intent of this review paper is to present the recent research progress on synthetic ester liquid in relation to the selected issues, most important for ester development in the authors’ opinion. The described issues are the breakdown performance of synthetic esters, lightning impulse strength and pre-breakdown phenomena of synthetic esters, synthetic esters-based nanofluids, combined paper-synthetic ester based insulating systems, application of synthetic ester for retro-filling and drying of mineral oil-immersed transformers, DGA(dissolved gas analysis)-based diagnosis of synthetic esters filled transformers as well as static electrification of synthetic esters. The different sections are based both on the data available in the literature, but above all on the authors’ own experience from their research work on synthetic ester liquids for electrical application purposes.

This article presents the results of the studies on positive streamers behavior in an insulation system of non-uniform electric field distribution where point-to-sphere electrode system was divided on two parts by placing the pressboard barrier in the middle of oil gap. The studies were performed for two synthetic esters as per IEC 61099, natural ester as per 62770, blended low viscosity ester and mineral oil as per IEC 60296. The experimental techniques used in the measurements were both electrical and optical ones. The results showed that independently of the liquids tested lightning strength of the insulation system increased circa 3 times in relation to the system without pressboard barrier. In turn in the waveforms of light emitted by the streamers propagating in esters no differences were observed between them. However in comparison to the mineral oil duration of streamer propagation is longer in esters and intensity of emitted light is higher. In general the results indicated quite similar properties of the streamers developing in all the liquids tested in the condition of the experiment.

This study presents findings on the influence of gap length distance on the lightning impulse breakdown voltage of three dielectric liquids of different chemical origins. The liquids were tested in a model electrode system with a quasi-uniform electric field distribution and a pressboard plate placed on the grounded electrode. The experimental studies were supported using calculations and simulations to show the individual relationships between the lightning impulse breakdown voltage and gap distance, which represent the so-called volume effect of the most stressed liquid. The results of the experiment, which involved four considered gap distances of 2, 4, 6, and 8 mm, show that a dynamic increase in lightning impulse breakdown voltage with an increase in gap distance is associated with mineral oil and bio-based hydrocarbons. However, similar trends were not observed for synthetic ester. Calculations that allowed us to assess the impact of gap length distance on lightning impulse breakdown voltage support the observations from the experimental studies. The curves obtained in this field can be considered in the process of designing insulating systems for transformers.

In this article, the lightning impulse breakdown (LIBV) behavior of two low pour point synthetic ester liquids is presented in comparison to a typical synthetic ester (TSE) at both positive and negative polarities. Traditional mineral insulating oil has also been considered for reference purposes. A detailed breakdown behavior analysis of the four test liquids under a nonuniform field (medium gap, point-plane electrode system) and quasi-uniform field (smaller gap, U-plane electrode system) is envisaged. The LIBV measurements based on the source voltage waveforms and light activity during the discharge process are presented. The Weibull breakdown failure rates and streamer velocity during the breakdown of different liquids for all the cases (± polarities and both electrode configurations) are reported in support of the discussions. In the case of nonuniform fields, the lightning breakdown voltage of the low pour point liquids is found to be higher than TSE s and is comparable to mineral oil (MO) under both polarities. While in the case of quasi-uniform field, the lightning breakdown voltage of the low pour point liquids is found to be lower than MO and comparable to the TSE under both polarities. These findings add to limited knowledge on the application of esters in cold countries and allow insulation designers to estimate the behavior of the low pour point synthetic ester liquids under lightning conditions.

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informuj?ce swoich czytelnik?w o najnowszych osi?gni?ciach naukowych i nowoczesnych rozwi?zaniach technicznych w Polsce i na ?wiecie, popularyzuje problemy techniczne oraz poszerza wiedz? i kultur? techniczn?.

W artykule przedstawiono wyniki badań nad inicjacją i przebiciem w biodegradowalnych cieczach dielektrycznych przy napięciu udarowym piorunowym. Do badań wykorzystano układ elektrod, w którym zarówno elektroda wysokonapięciowa jak i elektroda uziemiona wyposażone są w izolację stałą. Wyniki dotyczące estrów zestawiono z analogicznie uzyskanymi wynikami dla olejów mineralnych. W ramach analizy porównano napięcie inicjacji wyładowań i napięcie przebicia, a także czasy do przebicia oraz intensywność wyładowań.