Protection against lightning overvoltages in resonant grounded power distribution networks

AES Sul, a Brazilian electric distribution utility, has recently started a project focused on the installation of neutral resonant grounding devices at the medium voltage side of some substation transformers previously operated with solid grounded neutral. As a consequence of the expected increase of the voltage in the sound conductors during phase to ground faults, all the surge arresters must be replaced with ones with increased rating. In order to minimize the number of required surge arresters, a procedure has been developed for the estimation of the annual number of lightning events causing concomitant faults in more than one phase conductor. The paper describes the procedure, which takes into account all the main factors that have a significant influence on line insulation flashovers caused by lightning, and presents results obtained for the case of an overhead line with and without protection means

Estimation of the influence of direct strokes on the lightning performance of overhead distribution lines

When assessing the lightning performance of distribution lines, major attention is in general devoted to the induced voltages from nearby strikes rather than to direct events hitting the line, as the latter are always expected to cause a fault in the line. This paper proposes a Monte Carlo procedure capable to make it possible the evaluation of the overvoltage probability due to both indirect and direct strokes. The results are presented making reference to specific nodes of medium voltage overhead distribution networks, namely the locations of MV/LV transformers connections. The problem is of interest when a major upgrade of surge arresters is required, for instance when the neutral grounding practice needs to be changed (e.g. from grounded to resonant)

Selection of MV/LV transformers to be protected by surge arresters against indirect lightning overvoltages

The papers addresses the problem of locating surge protective devices in a medium voltage distribution network by means of an accurate computer model for the calculation of lightning induced overvoltages and a Monte Carlo statistical procedure. The indirect lightning performance of small network cells of different configuration are evaluated and used as a benchmark for the validation of the surge arrester locations provided by a genetic algorithm procedure. The obtained results appear useful for the lightning protection design of networks with complex topology

Associations of maternal bisphenol urine concentrations during pregnancy with neonatal metabolomic profiles

Background: Fetal exposure to bisphenols is associated with altered fetal growth, adverse birth outcomes and childhood cardio-metabolic risk factors. Metabolomics may serve as a tool to identify the mechanisms underlying these associations. We examined the associations of maternal bisphenol urinary concentrations in pregnancy with neonatal metabolite profiles from cord blood. Methods: In a population-based prospective cohort study among 225 mother–child pairs, maternal urinary bisphenol A, S and F concentrations in first, second and third trimester were measured. LC–MS/MS was used to determine neonatal concentrations of amino acids, non-esterified fatty acids (NEFA), phospholipids (PL), and carnitines in cord blood. Results: No associations of maternal total bisphenol concentrations with neonatal metabolite profiles were present. Higher maternal average BPA concentrations were associated with higher neonatal mono-unsaturated alkyl-lysophosphatidylcholine concentrations, whereas higher maternal average BPS was associated with lower neonatal overall and saturated alkyl-lysophosphatidylcholine (p-values &lt; 0.05).Trimester-specific analyses showed that higher maternal BPA, BPS and BPF were associated with alterations in neonatal NEFA, diacyl-phosphatidylcholines, acyl-alkyl-phosphatidylcholines, alkyl-lysophosphatidylcholine, sphingomyelines and acyl-carnitines, with the strongest effects for third trimester maternal bisphenol and neonatal diacyl-phosphatidylcholine, sphingomyeline and acyl-carnitine metabolites (p-values &lt; 0.05). Associations were not explained by maternal socio-demographic and lifestyle characteristics or birth characteristics. Discussion: Higher maternal bisphenol A, F and S concentrations in pregnancy are associated with alterations in neonatal metabolite profile, mainly in NEFA, PL and carnitines concentrations. These findings provide novel insight into potential mechanisms underlying associations of maternal bisphenol exposure during pregnancy with adverse offspring outcomes but need to be replicated among larger, diverse populations.</p