Outdoor insulation and gas-insulated switchgears

Introduction With the growth of the world’s population and faster-developing industries, larger amounts of electric energy are needed [1–6]. To reduce Joule losses at longer distances, voltages delivered by generators are increased with step-up power transformers, and electric energy is transported at large voltages [7,8]. Consequently, many ultra/extra AC/DC high-voltage transmission projects have been commissioned or are under construction in many countries: Canada (735 kV), Venezuela (800 kV), China (1100 kV), Japan (1100 kV), and India (1200 kV) [9–18]. For the power to be delivered to end-users, transmission grids, including towers, conductors, insulators, as well as substations, are essential [19–22]. The main equipment in substations includes, but is not limited to: power transformers, circuit breakers, surge arrestors, relays, insulators, disconnector switches, busbars, capacitor banks, batteries, wave trapper, switchyard, as well as protection, control, and metering instruments, etc. When the equipment is installed outside, it is refereed as an “outdoor substation” and an “indoor substation” when set inside a building. One of the main advantages of an indoor substation over an outdoor substation is the independence from meteorological impacts [23–25]. Nowadays, indoor substations are commonly gas-insulated substations (GIS), as they require a much smaller footprint [23]

Pre-Breakdown and Breakdown Behavior of Synthetic and Natural Ester Liquids under AC Stress

In the last decades, a large focus is being placed on the sustainability and safety of the power transformer spectrum. Ester liquids, which have interesting properties such as high fire point and biodegradability, are gaining needed attraction. Since in-service condition, thermal aging deteriorates the physicochemical and electrical properties of liquid dielectrics, it is important to study their long-term behavior. In this contribution, the pre-breakdown and breakdown behavior of ester fluids (synthetic and natural) under AC stress are investigated. Important characteristics, such as partial discharge pre-inception voltage, partial discharge inception voltage, breakdown voltage, average streamer velocity, and inception electric field, were assessed. The influence of the radius of curvature (of high voltage needle electrode) as well as the thermal degradation of typical ester liquids are also discussed. Mineral oil was also included in the tests loop as a benchmark for comparative purposes. It is found that the pre-inception voltage of ester liquids was, in most cases, higher than that of mineral oil. For a given radius of curvature, the streamer inception and breakdown voltages decreased with thermal aging. During the streamer initiation, the electric field at the electrode tip decreased with the increase in the radius of curvature. The velocity of the streamers seems to increase with the decrease in the radius of curvature. The period of vulnerability, the so-called “delay time”, seems to be independent of the aging or the radius of curvature for a given condition of the liquid

Prebreakdown and Breakdown Behaviour of Low Pour Point Dielectric Liquids Under Negative Lightning Impulse Voltage

In this article, some investigations on the prebreakdown and breakdown phenomena of low pour point insulating liquids under negative lightning impulse (LI) voltage are reported. The tested liquids include mineral oil (MO), a typical synthetic ester (TSE), and two low-pour point synthetic esters. These liquids underwent accelerated thermal aging. The nonaged and aged samples were subjected to LIs using a point-plane electrode arrangement. The discussions are focused on the initiation of partial discharges, propagation of streamers, and breakdown behavior in the nonaged and aged liquids. The investigated parameters include inception voltage, LI breakdown voltage, streamer acceleration voltage, and streamer velocity. The results are supported by the oscillographs of the light activity that is recorded during the discharge process. The prebreakdown phenomenon noticed in the TSE vis-à-vis mineral insulating oil is in line with the existing literature. Importantly, it is noticed that the inception and breakdown voltages of the nonaged low pour point synthetic esters are similar to nonaged MO. In addition, the inception and breakdown voltages of the aged low pour point synthetic esters are noticed to be higher than that of the aged MO. These results add to the arguments in favor of replacing MOs in power transformers

Analysis of Breakdown Voltage of Low Pour Point Synthetic Ester Insulating Liquids under Lightning Impulse Voltage of both Polarities

In this article, lightning impulse breakdown behaviour of two low pour point synthetic ester liquids is presented in comparison to a typical synthetic ester at both positive and negative polarities. Traditional mineral insulating oil has been also considered for reference purposes. A detailed breakdown behaviour analysis of the four test liquids under a non-uniform field (medium gap, point-plane electrode system) and quasi-uniform field (smaller gap, U-plane electrode system) is envisaged. The lightning impulse breakdown 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 non-uniform fields, the lightning breakdown voltage of the low pour point liquids is found to be higher than typical synthetic esters and is comparable to mineral oil 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 mineral oil and comparable to the typical synthetic ester under both polarities. These findings add to limited knowledge on the application of esters in cold countries and allow insulation designers to estimate the behaviour of the low pour point synthetic ester liquids under lightning conditions

"Hook"-calibration of GeneChip-microarrays: Chip characteristics and expression measures

<p>Abstract</p> <p>Background</p> <p>Microarray experiments rely on several critical steps that may introduce biases and uncertainty in downstream analyses. These steps include mRNA sample extraction, amplification and labelling, hybridization, and scanning causing chip-specific systematic variations on the raw intensity level. Also the chosen array-type and the up-to-dateness of the genomic information probed on the chip affect the quality of the expression measures. In the accompanying publication we presented theory and algorithm of the so-called hook method which aims at correcting expression data for systematic biases using a series of new chip characteristics.</p> <p>Results</p> <p>In this publication we summarize the essential chip characteristics provided by this method, analyze special benchmark experiments to estimate transcript related expression measures and illustrate the potency of the method to detect and to quantify the quality of a particular hybridization. It is shown that our single-chip approach provides expression measures responding linearly on changes of the transcript concentration over three orders of magnitude. In addition, the method calculates a detection call judging the relation between the signal and the detection limit of the particular measurement. The performance of the method in the context of different chip generations and probe set assignments is illustrated. The hook method characterizes the RNA-quality in terms of the 3'/5'-amplification bias and the sample-specific calling rate. We show that the proper judgement of these effects requires the disentanglement of non-specific and specific hybridization which, otherwise, can lead to misinterpretations of expression changes. The consequences of modifying probe/target interactions by either changing the labelling protocol or by substituting RNA by DNA targets are demonstrated.</p> <p>Conclusion</p> <p>The single-chip based hook-method provides accurate expression estimates and chip-summary characteristics using the natural metrics given by the hybridization reaction with the potency to develop new standards for microarray quality control and calibration.</p

Contribution to study of visible discharge initiation and development on the ice surface = Contribution à l'étude de l'apparition et du développement des décharges visibles à la surface de la glace

Le présent travail a pour objectif d'améliorer la connaissance des processus fondamentaux de décharges électriques à la surface de la glace. La compréhension de ces phénomènes peut aider à développer des outils numériques pour la prédiction des contournements des isolateurs recouverts de glace et à améliorer la conception des isolateurs à haute tension pour des applications dans des réseaux de transport d'énergie électrique dans les régions froides. Malgré un grand nombre d'études relatives à la performance électrique des isolateurs industriels sous des conditions givrantes, peu de travaux ont traité des processus fondamentaux. Dans ce contexte, ce projet de recherche a été initié par la Chaire CRSNG/Hydro-Québec/UQAC sur le givrage atmosphérique des équipements des réseaux électriques (CIGELE), dont les activités visent à accroître les connaissances de ces phénomènes. Dans cette étude expérimentale, des technologies sophistiquées de photographie à ultra haute vitesse sont appliquées dans le but d'observer et d'analyser pendant les premières nanosecondes les processus extrêmement rapides de l'apparition et du développement de décharge visible à la surface de la glace. Un modèle physique, qui consiste en deux électrodes métalliques à moitié submergées dans la glace, est utilisé pour les expériences. Des tensions d'essai en forme de choc de foudre sont appliquées. Les effets de plusieurs paramètres sont étudiés: conductivité de l'eau, température de la glace, uniformité de la surface de glace, taux de refroidissement, type d'accumulation de glace, polarité de la tension, forme d'onde, champ électrique pendant la période de refroidissement, distance entre les électrodes, rayon de courbure des électrodes, orientation de l'axe des électrodes. Les résultats montrent que la technologie des appareils photo à balayage de fente est adéquate pour l'étude des premières décharges visibles à la surface de la glace. Les expériences révèlent qu'il existe différents régimes pour les premières étapes des processus de décharge à la surface de la glace en fonction de la température de la glace et de la distance entre les électrodes. Des valeurs numériques sont relevées pour les conditions critiques de l'amorçage des décharges, pour la durée entre l'apparition des premières décharges et le contournement, ainsi que pour la vitesse de développement des décharges à la surface de la glace. Malgré le fait que les conditions expérimentales (modèle physique simplifié, tension en forme de choc de foudre) ne reproduisent pas parfaitement la situation d'une ligne de transport d'énergie électrique à haute tension (isolateur avec des formes complexes, tension sinusoïdale), des similitudes peuvent être identifiées entre les observations de terrain pendant des coupures de courant et des expériences en laboratoire

Evolution of countermeasures against atmospheric icing of power lines over the past four decades and their applications into field operations

The reliability and efficiency of power grids directly contribute to the economic well-being and quality of life of citizens in any country. This reliability depends, among other things, on the power lines that are exposed to different kinds of factors such as lightning, pollution, ice storm, wind, etc. In particular, ice and snow are serious threats in various areas of the world. Under certain conditions, outdoor equipment and hardware may experience various problems: cracking, fatigue, wear, flashover, etc. In actual fact, a variety of countermeasures has been proposed over the past decades and a certain number have been applied by utilities in various countries. This contribution presents the status and current trends of different techniques against atmospheric icing of power lines. A snapshot look at some significant development on this topic over the last four decades is addressed. Engineering problems in utilizing these techniques, their applications, and perspectives are also foreseen. The latest up-to-date review papers on the applications and challenges in terms of PhD thesis, journal articles, conference proceedings, technical reports, and web materials are reported

The predator defence system of an African king cricket (Orthoptera: Anostostomatidae): does it help to stink?

We examined the putative defence system of a king cricket, Onosandrus sp., in particular the efficacy of the noxious faeces against two types of predator: a lizard, the skink Mabuya striata (an active, diurnal forager), and the toad Bufo gutturalis (a nocturnal, ambush predator). Contrary to our predictions, the faeces did not act as a deterrent to either predator. Tongueflick trials with cotton scent applicators indicated that the skinks showed a heightened predatory response to king cricket faeces over king cricket integument, field cricket integument and an odourless control. We suggest that ‘primary’ defence mechanisms, such as nocturnal behaviour, cryptic colouration and immobility, are more effective than ‘secondary’ defence mechanisms, such as stridulation, kicking and defecation. Given that the noxious faeces already have a demonstrated role in inter- and intrasexual communication, we suggest that the assumed defensive role of the faeces is minor or an epiphenomenon.Keywords: Anostostomatidae, king cricket, defence behaviour, tongue-flicks, predatory behaviou

cricket (Orthoptera: Anostostomatidae):

does it help to stink