Applying series braking resistors to improve the stability of low inertia synchronous generators

Widely held concerns over the environmental impact of emissions from large fossil fuelled generating plants are serving to promote the connection of renewable or sustainable generation onto distribution networks. Many such generators are synchronous machines with low values of inertia, and thus possess short critical clearance times to avoid the onset of transient instability. With fault clearance times of up to 1s occurring in distribution networks, there is the potential for a growing problem as distributed generation makes up a larger proportion of installed capacity. This paper proposes the use of series braking resistors that are switched into circuit at the generator terminals as a means of improving transient stability, and thus avoid, or at least defer major upgrades to distribution system protectio

Comparison between flying capacitor and modular multilevel inverter

The paper describes the operational principle of flying capacitor and modular multilevel inverters. The detailed discussions of dc link capacitors voltage balancing methods for both inverters are given in order to enable fair comparison. The causes of dc link capacitors voltage imbalance in flying capacitor multilevel inverter with more than three levels are highlighted. Computer simulation is used to compare the performance of both inverters under several operating conditions

Comparison between two VSC-HVDC transmission systems technologies : modular and neutral point clamped multilevel converter

The paper presents a detail comparison between two voltage source converter high voltage dc transmission systems, the first is based on neutral point-clamped (also known as HVDC-Light) and the second is based on innovative modular multilevel converter (known as HVDC-Plus). The comparison focuses on the reliability issues of both technologies such as fault ride-through capability and control flexibility. To address these issues, neutral point-clamped and three-level modular converters are considered in both stations of the dc transmission system, and several operating conditions are considered, including, symmetrical and asymmetrical faults. Computer simulation in Matlab-Simulink environment has been used to confirm the validity of the results

Regulation of primary production in the Gulf of California through interaction of large-scale and local ocean processes [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): The suppression of primary productivity observed in eastern boundary ecosystems of the Pacific during El Nino episodes does not occur throughout the Gulf of California. On the contrary, analysis of the modern siliceous phytoplankton record from annually layered sediments and compilation of available primary productivity measurements indicate that production is significantly increased in the central Gulf during El Nino years compared to anti-El Nino years. Integrated observations of biological and physical variability during the spring of 1983, under the influence of the strong El Nino, show that very high primary productivity occurred along the eastern margin of the central Gulf. This resulted from the upwelling of a nutrient rich source provided by the locally formed Gulf water mass originating in the northern Gulf. Lower productivity and phytoplankton biomass were associated with the anomalous penetration of Tropical Surface Water along the western side of the Gulf

Emerald and Aquamarine Mineralization in Canada

This paper reviews the geology, mineralogy, and origin of the gem varieties of beryl, including emerald (green) and aquamarine (blue); it focuses on western Canada, especially the Yukon Territory, because this is where most of the recent discoveries have been made. However, emerald occurrences in Ontario are also considered, including Canada's first reported discovery in 1940. Beryl (B3Al2Si6O18) is relatively common and spatially associated with granites and granitic pegmatites, but emerald is rare because trace amounts of Cr and/or V are required (to replace Al in the crystal structure) and these elements generally do not occur in sufficient concentrations in granitic rocks. The geological conditions needed to bring Be into contact with Cr and/or V are briefly discussed, as are the factors to consider and techniques to use in exploring for gem-quality beryl. SUMMAIRE Le présent article traite de la géologie, de la minéralogie et de l'origine de variétés gemmifères de béryl (vert), dont l'émeraude et l'aigue-marine (bleue). Il traite principalement de l'Ouest canadien, particulièrement du Territoire du Yukon, région où la plupart des découvertes ont eu lieu. Toutefois, des découvertes faites en Ontario sont aussi considérées, incluant la première au Canada, en 1940. Le Béryl (B3Al2Si6O18) est relativement commun et associé aux granites et aux pegmatites granitiques, mais l'émeraude est rare parce qu'elle nécessite le remplacement de l'Al dans la structure cristalline du béryl par du Cr et/ou du V, et ces éléments ne se retrouvent généralement pas dans en concentrations suffisantes dans les roches granitiques. Les facteurs géologiques nécessaires pour que le Be et le Cr et/ou le V soient mis en contact font l'objet de discussion, tout comme les facteurs à considérer et les techniques à employer dans l'exploration de gisements de béryls gemmifères

Voltage compensation and power factor correction in distribution networks with DVR

The stability analysis and voltage regulation in distribution systems, as well as power quality problems such as voltage sags, swells, due to connection and disconnection of large loads, short circuits and the presence of non-linear loads, require of the consideration of adequate technical solutions. In this paper, a Dynamic Voltage Restorer ( DVR ) model based on a power converter scheme for voltage compensation due to the presence of sags of amplitude since 0.1pu to 0.9pu and swells with amplitude from 1.1pu to 1.9pu, and power factor correction in distribution networks is proposed. The results are verified through MATLAB & Simulink

Development of the Platysma Muscle and the Superficial Musculoaponeurotic System (Human Specimens at 8–17 Weeks of Development)

There is controversy regarding the description of the different regions of the face of the superficial musculoaponeurotic system (SMAS) and its relationship with the superficial mimetic muscles. The purpose of this study is to analyze the development of the platysma muscle and the SMAS in human specimens at 8–17 weeks of development using an optical microscope. Furthermore, we propose to study the relationship of the anlage of the SMAS and the neighbouring superficial mimetic muscles. The facial musculature derives from the mesenchyme of the second arch and migrates towards the different regions of the face while forming premuscular laminae. During the 8th week of development, the cervical, infraorbital, mandibular, and temporal laminae are observed to be on the same plane. The platysma muscle derives from the cervical lamina and its mandibular extension enclosing the lower part of the parotid region and the cheek, while the SMAS derives from the upper region. During the period of development analyzed in this study, we have observed no continuity between the anlage of the SMAS and that of the superficial layer of the temporal fascia and the zygomaticus major muscle. Nor have we observed any structure similar to the SMAS in the labial region

Reconsidering the roots, structure, and implications of gambling motives: An integrative approach.

Accurately identifying motives to gamble is crucial in the functional analysis of gambling behavior. In this study, a data-driven approach was followed to clarify the factor structure underlying a pool of motives for gambling, selected from the Gambling Motives Questionnaire-Financial (GMQ-F), and the Reasons for Gambling Questionnaire (RGQ), in a sample of regular problem and non-problem gamblers. Additionally, the role of gambling motives in the relationship between root behavioral activation/inhibition systems (BIS/BAS) and gambling severity, frequency, and preferences was explored using structural equation modelling (SEM). The present study identified Social, Financial, and Fun/thrill-related gambling motives factors, but also a fourth factor in which some positive and negative reinforcement-based motives were grouped into a single and broader Affect regulation factor. This Affect regulation factor shared variance both with BIS and BAS-related measures, and was the only direct predictor of disordered gambling symptoms. The Fun/thrill factor was directly related to frequency of participation in high-arousal, skill-based games, and all factors were related to participation in lower-arousal, chance games (with Social motives negatively predicting both participation in the latter and total severity). In the SEM model, measures of BIS/BAS sensitivity were connected to gambling behavior only through gambling motives. Based on measures of items' specificity, a shortened Spanish scale (the brief Gambling Motives Inventory, bGMI) is proposed to assess gambling motives in accordance with the observed 4-factor structure

Numerical analysis of stream function, vorticity and circulation for a rotating flow with rigid boundary

En este trabajo se obtienen y analizan los campos de las funciones vorticidad tangencial, circulación y corriente meridional, que se generan en el interior de un cilindro cerrado que tiene el fondo giratorio y la tapa superior y envolvente sin movimiento. Los resultados se presentan mediante gráficas en las que se comparan dichas funciones, para un número de Reynolds de 3x10 4 y para un factor de forma (alto/radio) del recipiente de 0.5, 1.0 y 2.0. Se encontró al comparar el sistema con relación geométrica 2 respecto al 1, que la función corriente disminuye 29.63%; que la circulación permanece constante y que la vorticidad se reduce un 65.91%. Por otro lado, al comparar el sistema con relación geométrica 0.5 respecto al de 1, se encontró que la función corriente aumenta 1.4 veces, que la circulación se incrementó 3.45 veces y que la vorticidad aumentó 0.7 veces. Los resultados anteriores dan una idea del comportamiento de las funciones corriente, circulación y vorticidad tangencial para las relaciones geométricas antes mencionadas, pero se requiere de un mayor análisis para poder utilizar estos resultados al caso particular de mezclado o de alguna otra aplicación práctica de ingeniería.The tangential vorticity function, circulation and meridian stream that form in a closed rotating cylinder are analyzed. The cylinder has a rotating bottom whereas the lateral surface and the top are fixed. The results are presented as graphs that compare the mentioned functions for different aspect ratios. The comparing aspect ratios: 0.5, 1.0 and 2.0. In comparing the 2.0 aspect ratio versus the 1.0 aspect ratio; it is found that the stream function diminished a 29.63%, whereas the circulation does not change and the vorticity decreases 65.91%. On the other hand comparison of the cylinder with aspect ratio 0.5 against the one with aspect ratio 1; gives that the stream function increases 1.4 times; that the circulation increases 3.45 times and the vorticirty increases 0.7 times. The analysis was made for a 3 x 104 Reynolds number. The mentioned results give an indication of the influence of the aspect ratio as to the motion inside the cylinder. Further investigation is required in order to apply the results to particular conditions of mixing or another practical application.Peer Reviewe