A Review on Synthetic Ester Liquids for Transformer Applications

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.

A supportive electrostatic model of the COVID-19 airborne transmission

A mechanism-oriented model is proposed here as a speculative but robust attempt to understand whether there might be any increased risk of electrostatically induced contamination, with relevant consequences from the epidemiological viewpoint. This could also be the case for the COVID-19 spreading because an amount of micro-sized droplet nuclei, often carrying net electric charge, are expected to be electro-dynamically involved in a physical process originated by the natural and unperceivable static electrification of human beings. The effects of the triboelectric charging have long been successfully tested because the phenomenon under examination is also implied in the genesis of the electrostatic discharge (ESD), a demanding key objective in the special context of electromagnetic compatibility (EMC). Therefore, the ultimate purpose of this technical paper is to provide valuable insights into infection control, building on what is already being done for maintaining static-safe environments. The stature of the applied model can be further appreciated because some currently observed climate-dependent and sex-linked different vulnerabilities to COVID-19 are critically examined by unique sound arguments. These ultimately focus attention on ambient relative humidity and worn shoes, the latter differing for typology, size and material, for their integrated control of the inadvertent human aptitude to buildup tribocharges. These would appear as a dreadful prerequisite for charge bearing droplets in the airborne state to be efficiently attracted/repelled according to the described electrostatic mechanism.

Kraft-Pulp Based Material for Electrical Insulation

<p>The dielectric properties of the electrical insulation material have a significant influence on the performance and reliability of components in electrical equipment. The influence of the chemistry and electronic structure of the different constituents of the kraft pulp (used in electrical insulation) on some dielectric properties is discussed in this paper. The studies and mechanisms discussed indicate that the presence of different wood polymers (cellulose, hemicellulose and lignin), have different effects on dielectric properties (static electrification and high frequency response). Our results show that the dielectric response of lignin is different compared with the response of hemicellulose and cellulose and this is also expected from the chemical structure of the different components. The lignin molecule has a higher polarizability at frequencies of significance for streamer inception and propagation. With spectroscopic ellipsometry measurements it has also been shown that the energy for electronic transitions in this spectral region is lower for lignin. The results also clearly indicate that the role of cellulose, lignin and hemicellulose should be further investigated for improving electrical breakdown strength of paper based insulation materials.</p>