17,955 research outputs found
Influence of ac ageing on space charge dynamics in LDPE
No full textPolymeric materials have been widely used as insulation in power industry due to their excellent electrical properties. However, these properties deteriorate in time irreversibly when the material is subjected to electric stress. Although space charge is believed to play an important role in ac ageing, exact mechanisms are poorly understood due to very limited experimental data. In the present work efforts have been made to investigate the influence of ac ageing on space charge dynamics in low-density polyethylene (LDPE). LDPE films with 200mm were aged at 50 kV/mm at 50 Hz for various times at ambient temperature. Space charge dynamics in the samples prior to and after ageing were monitored using the pulsed electroacoustic (PEA) technique under dc electric stress. The results indicate that there is a significant amount of homocharge accumulation in the unaged sample due to charge injection. These injected charges are the captured by the deep traps originated from the interface between crystalline and amorphous regions in LDPE. Ageing under ac condition does not necessarily lead to an increase in amount of charge in the bulk but leads to an increase in mobility of charge carriers. Chemical analysis by infrared spectroscope (FTIR) reveals there are chemical changes taken place in the bulk of the material after ac ageing. It is believed that the chemical changes introduce shallow traps which promote the movement of charge carriers in the bulk. Consequently, the injected charges spread across the sample
A power sharing series power BJT array with isolated low voltage control for AC power control applications
No full textA technique for a continuously variable AC resistance using a series BJT array is presented. This array provides high power dissipation capability and uniform voltage and power distribution across the individual transistors. The array, controlled using a set of optoisolators to maintain the electrical isolation between the control circuits and the power stage, could be used as the basis to develop several useful techniques including a solid state AC regulator with comparable performance to the commonly used ferro-resonant systems; a linear AC electronic load suitable for testing UPS and other power conditioners; and, in other AC power control applications such as switching capacitors in AC resonant circuits
Dina Maria viriginis ac Matris Saluatoris nostri Jesu Christi Historiam Epithome per Jllustrem pictorem
No full textDINA MARIA VIRIGINIS AC MATRIS SALUATORIS NOSTRI JESU CHRISTI HISTORIAM EPITHOME PER JLLUSTREM PICTOREM
Dina Maria viriginis ac Matris Saluatoris nostri Jesu Christi Historiam Epithome per Jllustrem pictorem ( - )
Cover ( - )
Titelseite ([1])
Abbildung 1 - 10 ([2])
Abbildung 11 - 19 ([12]
Experimental High-Frequency Parameter Identification of AC Electrical Motors
No full textIn order to predict conducted electromagnetic interference in inverter-motor drive systems, high-frequency (HF) motor models are requested and the involved parameters have to be available. In previous studies, the authors have presented an accurate HF model for induction motors and they have defined the procedures to identify the model parameters. In this paper, these results are extended to several types and sizes of industrial ac motors such as induction, synchronous reluctance (without interior permanent magnets), and brushless motors. The model parameter-identification procedure has been improved, and it is based on a least-squares data fitting applied to the measured magnitude and phase-frequency-response curves of the phase-to-ground and the phase-to-neutral impedances. The aim of this paper is to provide quick indications to select the suitable values of the HF model parameters, with reference to the size and type of the ac motor, to evaluate the HF voltage and current components in inverted-fed ac motor system
Using the AC Drive Motor as a Transducer for Detecting Electrical and Electromechanical Faults
No full textCondition monitoring of AC motors is a subject area that has received extensive research. Whether this monitoring is carried out on a scheduled basis by engineer intervention, or continuously using an on-line unit, the results of this testing enable preventative maintenance work to be a carried out earlier, before any major failure occurs. Monitoring using vibration analysis is the most common and depending on the plant, can be done once or twice a year. This is usually limited to the condition of motor bearings and is not commonly used to detect failures in the motor electromagnetic systems. Monitoring units that use motor current measurements are also available, but these are less widely-used and usually on major plant motors (>250kW for example) that have a large capital outlay to replace.
The industry drivers – as always – are maximum plant and machinery uptime, with the minimal amount of scheduled maintenance. If maintenance is carried out too regularly, costs rise significantly not only due to the maintenance activity itself, but disruption to production schedules. Maintenance schedules that are too infrequent can result in an unacceptable rise in total failures of plant that are unexpected and may cause a significant amount of production disruption and downtime, especially if this occurs during out-of-hours working time. However, industry now faces another big challenge and one that has had a good share of exposure over the last few years. It is of course, the drive to reduce carbon emissions and with it the amount of energy that a plant itself consumes. What has brought this more to the fore recently is the significant rise in energy costs. Whilst product margins have to remain the same, many companies energy costs have seen a two to three-fold increase in energy budgets in the last few years alone. For industry processes that have a significant amount of fan and pump applications, the manufacturers of low-cost AC inverters have saturated the lower-performance market of inverter drives such that any drive can control these type of fan and pump applications, where accurate speed control is not a major driver.
Unfortunately, this can be a step backwards for end-users of plant that use equipment to monitor motor condition via motor current signals. Additionally, vibration analysis that relies upon ‘base-lining’ motor data when the AC motor is running at base speed may not give accurate readings when the motor is under inverter control and running at a different speed.
For manufacturers of AC inverter drives in this low-end market, it can be difficult to sell a product from one manufacturer over another without the unit having a “USP”, or Unique Selling Proposition. Most decisions taken on inverter equipment purchase at this level are usually in favour of the equipment that costs the least to purchase. Credibility of manufacturers based on product history and perceived reliability cuts little ground with an ever cost-conscious industry.
This is where the research into diagnosis of faults on inverter driven motor systems can provide just this USP for manufacturers. If the incorporation of on-line diagnosis for simple inverter applications can be brought to a typical inverter unit at a reasonable cost, the manufacturer who can offer this gains a unique foothold in the marketplace – a drive that can monitor and signal that the motor it is driving is showing signs of early failure.
It will be sensible to limit this research to simple inverter applications as high-end inverter drives that operate equipment such as high-speed printing presses, rotary shears will be more difficult to model and simulate than a fan or pump application.
It is hoped that a typical inverter drive can relay enough detailed information about the load which it is driving to allow this to be used for abnormal motor load conditions as this will provide a platform on which to extend the research beyond this MSc and into the realms of incorporating such technology into a drive manufacturers equipment. If this can be done without major modification to an inverter, then it may be easier to implement in equipment offered by different manufacturers.
It is quite possible that this technology could be licensed under a name that guarantees the performance of the condition monitoring algorithms and reliability from one drive manufacturer to another
Compression of time during smooth pursuit eye movements
No full textHumans have a clear sense for the passage of time but while implicit motor timing is quite accurate explicit timing is prone to distortions particularly during action (Wenke & Haggard 2009) and saccadic eye movements (Morrone Ross & Burr 2005) Here we investigated whether perceived duration is also affected by the execution of smooth pursuit eye movements showing a compression of apparent duration similar to that observed during saccades To this end we presented two brief bars that marked intervals between 100 and 300 ms and asked subjects to judge their duration during fixation and pursuit We found a compression of perceived duration for bars modulated in luminance contrast of about 32% and for bars modulated in chromatic contrast of 14% during pursuit compared to fixation Interestingly Weber ratios were similar for fixation and pursuit if they are expressed as ratio between JND and perceived duration This compression was constant for pursuit speeds from 7 to 14 deg/s and did not occur for Intervals marked by auditory events These results argue for a modality-specific component in the processing of temporal information (C) 2010 Elsevier Ltd All rights reserve
Imagens de Otto Maria Carpeaux: esboço de biografia
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas, Programa de Pós-Graduação em História, Florianópolis, 2015.Este esboço de biografia procura citar algumas imagens de Otto Maria Carpeaux: construções biográficas de naturezas múltiplas, elaboradas em contextos, por atores e sob condições igualmente díspares. Está constituído a partir de uma visão crítica da História, o que permite que ?outras imagens?, fragmentárias e não monumentais, também tenham espaço. Em diálogo com o princípio da montagem, este esboço apresenta-se em duas partes. Na primeira, Imagens possíveis, estão citadas as imagens elaboradas em vida e post mortem acerca do austríaco-brasileiro que nasceu em Viena em 1900, se exilou no Brasil em 1939 e morreu no Rio de Janeiro, em 1978. Na segunda, Montagens possíveis, apresentam-se duas possibilidades de exercício biográfico: pela leitura alegórica do documentário O velho e o Novo (Otto Maria Carpeaux), entendido como instrumento de intervenção no contexto ditatorial brasileiro e de uma reelaboração biográfica concernentes às suas experiências europeias; e pelo Caderno de imagens críticas, registro dos encontros em Carpeaux pelo meio de imagens críticas produzidas a partir da cesura do presente.Abstract : This biographical sketch attempts to quote some images of Otto Maria Carpeaux: various types of biographical constructions, carried out in different contexts by disparate authors under conditions just as distinct. It stems from a critical view of history, allowing for ?other images? fragmented and non-monumental ? to share the space.In dialogue with the montage principle, this sketch has two parts. The first, Possible Images, quotes the images produced during and after the life of the Austrian-Brazilian, who was born in Vienna in 1900, went to Brazil in exile in 1939 and died in Rio de Janeiro in 1978. The second part, Possible Montages, presents two possibilities of a biographical exercise: through the allegorical reading of documentary O Velho e o Novo (Otto Maria Carpeaux), understood as an instrument of intervention in the Brazilian dictatorship context and as a biographical retelling of the author?s European experiences; and through my Scrapbook of Critical Images, a record of the encounters in Carpeaux through critical images produced from the caesura of the present
Saverio Celentano e la disputa accademica «a lode del Venerando Nome di Maria»
No full textLa Biblioteca La Magna Capitana di Foggia (BPF) conserva il copioso lascito manoscritto di Saverio Celentano (1698-1760), personalità eminente per la storia sociale, politica e istituzionale foggiana dei suoi tempi. Nel ms. 34 figurano in doppia redazione (e una volta sotto forma di minuta) una «Introduzione dell’Accademia del nome di Maria à 13 settembre 1733 fatta dal dottor Saverio Celentano Principe di detta Ac- cademia» e un «Discorso accademico» tenuto da Celentano su cui mi soffermerò a breve
Qualidade da farinha de mandioca produzida no Vale do Juruá/AC.
No full textEste trabalho avalia a qualidade da farinha de mandioca produzida no Vale do Juruá/AC
Avaliação de germoplasmas de tomate para resistência à murcha bacteriana em Rio Branco-AC.
No full textNo estado do Acre a murcha bacteriana é o principal fator limitante ao cultivo do tomateiro pois o ataque da murchadeira é mais intenso na época chuvosa, quando se forma um microclima favorável ao aparecimento da doença. Este estudo objetiva selecionar cultivares tolerantes à murcha bacteriana nas condições climáticas de Rio Branco (AC)
- …
