A Physical Model for Inception and Propagation of Upward Lightning Leader from a 1200 kV AC Power Transmission Line

UHV power transmission lines have high probability of shielding failure due to their higher height, larger exposure area and high operating voltage. Lightning upward leader inception and propagation is an integral part of lightning shielding failure analysis and need to be studied in detail. In this paper a model for lightning attachment has been proposed based on the present knowledge of lightning physics. Leader inception is modeled based on the corona charge present near the conductor region and the propagation model is based on the correlation between the lightning induced voltage on the conductor and the drop along the upward leader channel. The inception model developed is compared with previous inception models and the results obtained using the present and previous models are comparable. Lightning striking distances (final jump) for various return stroke current were computed for different conductor heights. The computed striking distance values showed good correlation with the values calculated using the equation proposed by the IEEE working group for the applicable conductor heights of up to 8 m. The model is applied to a 1200 kV AC power transmission line and inception of the upward leader is analyzed for this configuration.

Computation of power released during corona treatment on polymeric insulators under ac and dc excitation

With increasing energy demand, it necessitates to generate and transmit the electrical power with minimal losses. High voltage power transmission is the most economical way of transmitting bulk power over long distances. Transmission insulator is one of the main components used as a mechanical support and to electrically isolate the conductor from the tower. Corona from the hardware and conductors can significantly affect the performance of the polymeric insulators. In the present investigation a methodology is presented to evaluate the corona performance of the polymeric shed material under different environment conditions for both ac and dc excitation. The results of the comprehensive analysis on various polymeric samples and the power released from the corona electrode for both the ac and dc excitation are presented. Some interesting results obtained from the chemical analysis confirmed the presence of nitric acid species on the treated sample which in long term will affect the strength of the insulator, also the morphological changes were found to be varying for different experimental conditions. (C) 2015 The Authors. Published by Elsevier Ltd.

High Performance Modulation of High-Frequency AC Link Inverter

Inverters with high voltage conversion ratio are used in systems with sources such as batteries, photovoltaic (PV) modules or fuel cells. Transformers are often used in such inverters to provide the required voltage conversion ratio and isolation. In this paper, a compact high-frequency (HF) transformer interfaced AC link inverter with lossless snubber is discussed. A high performance synchronized modulation scheme is proposed for this inverter. This modulation addresses the issue of over-voltage spikes due to transformer leakage inductance and it is shown that the circuit can operate safely even when the turn-on delay, such as dead-time, is not used in the HF rectifier section. The problem of spurious turn-on in the HF inverter switches is also mitigated by the proposed modulation method. The circuit performance is validated experimentally with a $900W$ prototype inverter.

A Simple Hysteretic Energy Harvesting Method for Nonneutral AC Switches in Load Automation

This paper presents a simple hysteretic method to obtain the energy required to operate the gate-drive, sensors, and other circuits within nonneutral ac switches intended for use in load automated buildings. The proposed method features a switch-mode low part-count self-powered MOSFET ac switch that achieves efficiency and load current THD figures comparable to those of an externally gate-driven switch built using similar MOSFETS. The fundamental operation of the method is explained in detail, followed by the modifications required for practical implementation. Certain design rules that allow the method to accommodate a wide range of single-phase loads from 10 VA to 1 kVA are discussed, along with an efficiency enhancement feature based on inherent MOSFET characteristics. The limitations and side effects of the method are also mentioned according to their levels of severity. Finally, experimental results obtained using a prototype sensor switch are presented, along with a performance comparison of the prototype with an externally gate-driven MOSFET switch.

Growth Mechanism And Corrosion Behavior Of Ceramic Coatings On Aluminum Produced By Autocontrol Ac Pulse Peo

Ceramic coatings are produced on aluminum alloy by autocontrol AC pulse Plasma Electrolytic Oxidation (PEO) with stabilized average current. Transient signal gathering system is used to study the current, voltage, and the transient wave during the PEO process. SEM, OM, XRD and EDS are used to study the coatings evolution of morphologies, composition and structure. TEM is used to study the micro profile of the outer looser layer and inner compact layer. Polarization test is used to study the corrosion property of PEO coatings in NaCl solution. According to the test results, AC pulse PEO process can be divided into four stages with different aspects of discharge phenomena, voltage and current. The growth mechanism of AC PEO coating is characterized as anodic reaction and discharge sintering effect. PEO coating can increase the corrosion resistance of aluminum alloy by one order or two; however, too long process time is not necessarily needed to increase the corrosion resistance. In condition of this paper, PEO coating at 60 min is the most protective coating for aluminum alloy substrate. (C) 2008 Elsevier B.V. All fights reserved.

Numerical-simulation of ac plasma-arc thermodynamics

A mathematical model and approximate analysis for the energy distribution of an ac plasma arc with a moving boundary is developed. A simplified electrical conductivity function is assumed so that the dynamic behavior of the arc may be determined, independent of the gas type. The model leads to a reduced set of non-linear partial differential equations which governs the quasi-steady ac arc. This system is solved numerically and it is found that convection plays an important role, not only in the temperature distribution, but also in arc disruptions. Moreover, disruptions are found to be influenced by convection only for a limited frequency range. The results of the present studies are applicable to the frequency range of 10-10(2) Hz which includes most industry ac arc frequencies. (C) 1994 Academic Press, Inc.

Novus orbis regionum ac insularum veteribus incognitarum : una cum tabula cosmographica & aliquot alijs consimilis argumenti libellis, quorum omnium catalogus sequenti patebit pagina : his accessit copiosus rerum memorabilium index

Esta coleção, geralmente conhecida por Grineu, foi compilada por Johann Huttich e publicada por Simon Grineu, que também escreveu e assinou o prefácio. A primeira edição, "muito e rara e de inestimável valor", segundo Borba de Moraes, foi publicada na Basiléia por Jo. Hervagium, em 1532. Dessa edição, a Biblioteca Nacional do Rio de Janeiro possui um exemplar que pertencia à Biblioteca da Ajuda. A obra foi reimpressa em Paris, em 1532, e novamente na Basiléia, em 1537. Esta edição foi acrescida da carta de Maximilianus Transilvanus, secretário de Carlos V, ao Cardeal de Salzburgo. Dentre as várias ediçoes, a mais completa é a de 1555. Relata as grandes navegações e as expedições de Cristovão Colombo, Pedro Alonso, Pinzoni, Americo Vespucio, dentre outros

Characteristics of an AC Three-Phase GlidArc Plasma Generator

M. tullii ciceronis orationum : cum optimis ac postremis exemplaribus accurate collatus

Titulo do v. 2 : m. tulli ciceronis orationes

Io. gottl. heineccii, iureconsulti quondam celeberrimi : recitationes in elementa iuris civilis secundum ordinem institutionum, accedunt io. christ. gottl. heineccii ... commentarius de vita, fatis ac scriptis b. parentis, auctior emendatior christiani thomasii, delineatio historiae juris nec non burc. gottelf. struvii, bibliotheca juris selectissima cum notis hen. contelmanni, ubi praestantiora iurisconsultorum opera ad nostra usque tempora referuntur

Título Uniforme : Corpus Juris Civilis. Institutas.

Hugonis grotii de jure belli ac pacis :libri tres, cum annotatis auctoris, nec non j.f. gronovii notis, & j. barbeyracii animadversionibus, commentariis insuper locupletissimis henr. l.b. de cocceii, sacrae regiae majestati borussicae, quondam a consiliis secretioribus, sub titulo grotii illustrati antea editis, nunc ad calcem cujusque capitis adjectis : insertis quoque observationibus samuelis l.b. de coceii, henrici fillii, regni borussici cancellarii, ... adduntur tandem ipsius grotti dissertatio de mari libero, ac libellus singularis de aequitate, indulgentia et facilitate

Titulo do volume 5: Samuelis l.b. de cocceii, summi regni borussici canncellari... introductio ad Henrici l.b. de cocceii grotium illustratum.

Missale romanum ex decreto sacrosancti concilii tridentini restitutum :cum omnibus aliorum sanctorum missis novissimè per summos pontifices enarratis, ac universis ditionibus fidelissimorum lusitaniae regum hucusquè pro utroque clero concessis locupletatum : PII V. Pont. Max. Jussu editum, Clementis VIII. et Urbani VIII. Auctoritate Recognitum

Pagina de rosto e texto impressos em vermelho e preto

Control de convertidor DC/AC trifásico por eliminación selectiva de armónicos

[ES]El objetivo de este trabajo es el desarrollo de un sistema de control de un inversor trifásico mediante una modulación PWM, basada en la eliminación selectiva de armónicos. En este documento se describen las técnicas empleadas en los sistemas actuales, los métodos para implementar el sistema de control propuesto, las tareas a realizar durante el desarrollo del proyecto, una estimación económica y los resultados obtenidos. Con esto, se pretende demostrar que la eficiencia de la solución propuesta es mayor que la de los métodos actuales y que es posible implementarla de una manera sencilla.