Pre-breakdown streamer propagation and breakdown characteristics of refined bleached and deodorized palm oil under lightning impulse voltage

This paper presents the investigation on the breakdown characteristics and pre-breakdown streamer propagation of Palm Oil (PO) impregnated aged pressboard under positive lightning impulse voltages. The experimental work was carried out under a non-uniform field with needle-plane electrodes configuration. The streamer stopping length and breakdown voltage of 2 types of refined, bleached, and deodorized palm oil were examined in the presence of new and aged pressboards. The pressboard was placed in parallel to the needle-plane electrode at a gap distance of 50 mm. The lightning breakdown voltage was applied to the samples based on 1 shot per step rising voltage method under positive polarity as per IEC 60897. The presence of impregnated pressboard in both PO slightly increases the 50% positive lightning breakdown voltages. PO impregnated pressboards have lower 50% positive lightning breakdown voltages than MO. After subjected to ageing, the positive lightning breakdown voltages for PO and MO impregnated pressboards decrease. In the presence of aged pressboard, the streamers in PO generally propagate further than MO at the same voltage level

Pre-breakdown streamer propagation and positive lightning breakdown characteristics of palm oil impregnated aged pressboard

This paper presents the investigation on the breakdown characteristics and pre-breakdown streamer propagation of Palm Oil (PO) impregnated aged pressboard under positive lightning impulse voltages. The experimental work was carried out under a non-uniform field with needle-plane electrodes configuration. The streamer stopping length and breakdown voltage of 2 types of refined, bleached, and deodorized palm oil were examined in the presence of new and aged pressboards. The pressboard was placed in parallel to the needle-plane electrode at a gap distance of 50 mm. The lightning breakdown voltage was applied to the samples based on 1 shot per step rising voltage method under positive polarity as per IEC 60897. The presence of impregnated pressboard in both PO slightly increases the 50% positive lightning breakdown voltages. PO impregnated pressboards have lower 50% positive lightning breakdown voltages than MO. After subjected to ageing, the positive lightning breakdown voltages for PO and MO impregnated pressboards decrease. In the presence of aged pressboard, the streamers in PO generally propagate further than MO at the same voltage level

High Voltage Insulating Materials-Current State and Prospects

Studies on new solutions in the field of high-voltage insulating materials are presented in this book. Most of these works concern liquid insulation, especially biodegradable ester fluids; however, in a few cases, gaseous and solid insulation are also considered. Both fundamental research as well as research related to industrial applications are described. In addition, experimental techniques aimed at possibly finding new ways of analysing the experimental data are proposed to test dielectrics

Performance Assessment of Cellulose Paper Impregnated in Nanofluid for Power Transformer Insulation Application: A review

Insulation cellulose paper is a basic measure for a power transformer’s remaining useful life, and its advantageous low cost, electrical, and mechanical properties have made it an extensive insulation system when impregnated in a dielectric liquid. Cellulose paper deteriorates as a result of ageing due to some chemical reactions like pyrolysis (heat), hydrolysis (moisture), and oxidation (oxygen) that affects its degree of polymerization. The condition analysis of cellulose paper has been a major concern since the collection of paper samples from an operational power transformer is almost impossible. However, some chemicals generated during cellulose paper deterioration, which were dissolved in dielectric liquid, have been used alternatively for this purpose as they show a direct correlation with the paper’s degree of polymerization. Furthermore, online and non-destructive measurement of the degree of polymerization by optical sensors has been proposed recently but is yet to be available in the market and is yet generally acceptable. In mitigating the magnitude of paper deterioration, some ageing assessments have been proposed. Furthermore, researchers have successfully enhanced the insulating performance of oil-impregnated insulation paper by the addition of various types of nanoparticles. This study reviews the ageing assessment of oil-paper composite insulation and the effect of nanoparticles on tensile strength and electrical properties of oil-impregnated paper insulation. It includes not only significant tutorial elements but also some analyses, which open the door for further research on the topic

Pre-breakdown phenomena in ester-based fluids for potential application in transformers serving in cold climatic regions

In recent years, environmental constraints have become major elements to be considered in the choice of insulating liquids. To address this concern, the present research has been directed towards biodegradable insulation liquid alternatives to mineral oils. Despite the advancement of knowledge on biodegradable oils, the application of low pour point esters in the insulation system of the transformers operating in cold climates remains a challenge. Apart from many positive characteristics of esters, the study of the propagation of "streamers" have indicated the poor performance when compared to mineral oils. To contribute the advancement of knowledge in this field, prebreakdown and breakdown phenomena of thermally aged low pour point esters have been studied. Tests with mineral oil were carried out in parallel for comparison. The breakdown voltage measurements were performed (in a needle-plane electrode configuration), at different aging conditions with different high voltage (HV) electrode tip radii under AC voltage. This allows studying the effect of chemical impurities (aging by-products) as assessed by some physicochemical properties (acidity, particles count, turbidity, and UV spectroscopy) on partial discharges (PD) and breakdown characteristics. The complete analysis is carried out for the liquids having pour point less than -50°C with those including a mineral oil (MO) and two synthetic ester liquids (SE1 and SE2). Changes in discharge properties such as particle partial discharge inception voltage (PDIV), breakdown-streamers inception voltage, inception electric field, and breakdown voltage are reported as a function of the HV electrode tip radius and aging factor. To assess the level of liquid degradation, UV spectroscopy, turbidity, particle count, and acidity measurements were performed. To highlight the influence of aging on streamer inception, suitable correlations have been reported between decay products, acidity, and PDIV. It is observed that the breakdown properties of SE1 are better than that of SE2 and comparable to MO. This underlines the potential use of the SE1, at least with regard to pre-breakdown phenomena. Importantly, the acidity and concentration of decay products evolve linearly with PD inception and streamer propagation regardless the tip radius. The calculation of the electrical onset in insulating fluids is of general interest for designing HV liquid filled equipment. As the physical processes of the breakdown are not yet fully understood, design engineers could rely these correlations when calculating the onset strength of a specific design layout. Depuis quelques années, les contraintes environnementales sont devenues des éléments majeurs à prendre en compte dans le choix des liquides isolants. C’est pourquoi la recherche sur les isolants liquides biodégradables, alternatives aux huiles minérales, connait un engouement. Malgré l’avancée des connaissances sur les huiles biodégradables, l'application d'esters à bas point d'écoulement pour l'isolation des transformateurs exploités dans les régions à climat froid reste un défi. Malgré de nombreuses caractéristiques positives des esters, des études concernant la propagation des « streamers » ont indiqué qu’elle se comporteraient moins bien que les huiles minérales. Pour contribuer à l’avancée des connaissances dans ce domaine, les tensions de préclaquage et de claquage d'esters à bas point d'écoulement vieillis thermiquement ont été étudiées. Des essais avec huile minérale ont été réalisés en parallèle à des fins de comparaison. Les mesures de tension de claquage ont été effectuées (dans une configuration d'électrode pointe-plan), à différentes durées de vieillissement avec différents rayons de l’électrode haute tension (HT) sous tension alternative. Cette approche permet d'étudier l'effet des impuretés chimiques (sous-produits du vieillissement) évaluées par certaines propriétés physico-chimiques (acidité, nombre de particules, turbidité et spectroscopie UV) sur les caractéristiques de décharges partielles (DP) et de dégradation. L'analyse est effectuée pour des liquides ayant un point d'écoulement inférieur à -50°C, une huile minérale (MO) et deux esters synthétiques (SE1 et SE2). Les changements dans les propriétés des décharges telles que la tension seuil d’apparition de décharges partielles (PDIV), la tension d’apparition des décharges streamers, le champ électrique seuil d’apparition des décharges électriques et la tension de claquage, sont rapportés en fonction du rayon de l'électrode HT et du degré de vieillissement. Pour évaluer le niveau de dégradation des liquides, des mesures par spectroscopie UV-visible, de turbidité, du nombre de particules et d'acidité ont été effectuées. Pour mettre en évidence l'influence du vieillissement sur l’initiation des décharges streamers, des corrélations appropriées ont été rapportées entre les produits dissous, l'acidité et le PDIV. Il est possible d’observer que les propriétés de claquage de SE1 sont meilleures que celles de SE2 et comparables à celles de MO. Ce qui souligne le potentiel d’utilisation du SE1, à tout le moins en ce qui a trait aux phénomènes de pré-claquages. Il est également important de mentionner que l’acidité et la quantité relative des produits dissous évoluent de manière linéaire avec l'apparition des DP et la propagation des décharges streamers, indépendamment du rayon de l’électrode HT. Le calcul du champ électrique d’initiation des décharges dans les fluides isolants est d'un intérêt général pour la conception d'équipements HT remplis de liquide. Étant donné que les processus physiques du claquage ne sont pas encore entièrement compris, les ingénieurs concepteurs pourraient se fier à ces corrélations pour calculer le seuil d’initiation d’une disposition spécifique

Effect of water on electrical properties of Refined, Bleached, and Deodorized Palm Oil (RBDPO) as electrical insulating material

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water

Comparison of the vocabularies of the Gregg shorthand dictionary and Horn-Peterson's basic vocabulary of business letters

This study is a comparative analysis of the vocabularies of Horn and Peterson's The Basic Vocabulary of Business Letters1 and the Gregg Shorthand Dictionary.2 Both books purport to present a list of words most frequently encountered by stenographers and students of shorthand. The, Basic Vocabulary of Business Letters, published "in answer to repeated requests for data on the words appearing most frequently in business letters,"3 is a frequency list specific to business writing. Although the book carries the copyright date of 1943, the vocabulary was compiled much earlier. The listings constitute a part of the data used in the preparation of the 10,000 words making up the ranked frequency list compiled by Ernest Horn and staff and published in 1926 under the title of A Basic Writing Vocabulary: 10,000 Words Lost Commonly Used in Writing. The introduction to that publication gives credit to Miss Cora Crowder for the contribution of her Master's study at the University of Minnesota concerning words found in business writing. With additional data from supplementary sources, the complete listing represents twenty-six classes of business, as follows 1. Miscellaneous 2. Florists 3. Automobile manufacturers and sales companie