Showing papers by "CHESF published in 2011"
1 Oct 2011
TL;DR: In this article, the authors presented and compared the electromechanical effects produced by the inrush and short-circuit currents in the transformers windings, taking into account the same magnitude of current.
Abstract: This paper presents the mechanical effect on transformers when subjected to one of the power quality indicators, i.e., the electromagnetic transients. A common reason for internal faults in transformers windings is the weak insulation. This effect can be caused and accelerated by the electromechanical efforts produced by the inrush and short-circuit currents. Even though the transformer energizing is considered a normal operation, it produces high currents and this phenomenon significantly reduces the transformer life expectancy and may even lead to its instantaneous or timing destruction. Moreover, taking into account the same magnitude of current, the inrush currents can produce greater forces than those caused by short-circuit currents. Therefore, this papers aims to present and compare the electromechanical effects produced by the inrush and short-circuit currents in the transformers windings. To conduct this research, FLUX software in its 3D version, based on the finite element method (FEM) will be used. To highlight the overall model and the software performance, a laboratory 15 kVA transformer is utilized. It has been built with concentric double-layer windings and ferromagnetic core with three columns.
17 citations
24 Jul 2011
TL;DR: In this article, the authors present harmonic distortion measurements in several countries taken during live televised matches of the 2010 Soccer World Cup held in South Africa, and compare the latest measurements with previous events and make some considerations regarding future trends.
Abstract: This paper presents harmonic distortion measurements in several countries taken during live televised matches of the 2010 Soccer World Cup held in South Africa. The paper provides an analysis of the components involved in the increase of total harmonic distortion of current and voltage. The work also compares the latest measurements with previous events and makes some considerations regarding future trends. Measurements from Brazil, Italy, Netherlands and Australia are presented and briefly discussed. Lessons learned from these observations could potentially improve our understanding of the impact of customer equipment and customer behavior on harmonic levels and assist in managing waveform distortion now and in the future.
9 citations
TL;DR: Investigation of the reproductive behavior of this Anostracan in different periods (dry and rainy) showed the reproduction is sexed, and the number of produced cysts is related to the size of the female.
Abstract: The reproductive behavior of fresh water Anostracan has not been massively studied by the carcinology specialized literature, regarding especially the Dendrocephalus brasiliensis Pesta, 1921, about which there are abundant studies only on the geographical distribution of that Anostracan. The objective of this research was to investigate the reproductive behavior of this Anostracan in different periods (dry and rainy). For this, mature individuals of both sexes were used. They were collected in four ponds of the Fish Farming Station of Paulo Afonso (FFSPA), by monthly capture in each pond, within the period from December 2004 to November 2005. The reproduction type was observed by placing some females in aquariums with males and placing the other ones individually, starting from the nauplii phase, where they stayed for 15 days (reproductive age). The individuals' sexual proportion was calculated by the relative frequencies of males and of females, every month, for the whole collection period. At 10 days cysts production is possible and the number of produced cysts is related to the size of the female. The ratio male:female in the studied period was of 1 male to 1.07 female. The proportion male:female was 51.75% female to 48.25% male along the year. The observation of the reproductive behavior showed the reproduction is sexed. KEYWORDS: crustacean; fresh water; reproduction; Thamnocephalidae.
5 citations
TL;DR: The analysis of variance in taxonomic richness revealed higher averages for the dry season and for high tides, indicating conditions of environmental equilibrium in the studied area.
Abstract: Studies aimed at determining phytoplankton composition, biomass, ecology and some physical-chemical characteristics of the Sao Francisco estuary were conducted at 7 sampling stations located in Piacabucu-Alagoas (10o25’-10°30’S and 36o23’-36o27W) during the rainy and dry seasons. The samples were obtained from the subsurface layer at neap and spring tides, during high and low tides, using a plankton net with 45 um mesh size. The waters from this estuary are characterized by low salinity, high temperatures, pH between alkaline and slightly acid, transparency greater than 1 meter. The phytoplankton was composed of 205 taxa, mainly distributed between the divisions Chlorophyta and Bacillariophyta, considered the most representative. The diatom Aulacoseira ambigua was considered dominant. Most of the species identified were planktonic and of freshwater origin. Specific diversity and equitability were considered average and high, indicating conditions of environmental equilibrium in the studied area. The analysis of variance in taxonomic richness revealed higher averages for the dry season and for high tides. Chlorophyll a content ranged between 0.4ug/L and 24,4ug/L. The annual variation of phytoplankton and physical-chemical parameters was related to rainfall.
4 citations