9,947 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
Avaliação dos níveis de infestação da broca Hypothenemus hampei (Ferrari, 1867) em linhagens e progênies de café, em Rio Branco, AC.
No full textEste trabalho tem a finalidade de avaliar os níveis de infestação da broca do café nos materiais genéticos introduzidos através de ações de pesquisa que visam fornecer indícios de resistência ou tolerância, para complementar as informações que embasarão futuras recomendações
Infestação e medidas preventivas no manejo da broca do cafeeiro Hypothenemus hampei (Ferrari, 1867) nas linhagens de café Robusta e Conilon em Rio Branco-AC.
No full textEste trabalho recomenda as medidas preventivas que devem ser adotadas no manejo da broca do cafeeiro nas linhagens de café Robusta e Conilon em Rio Branco-AC
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
O nosso CAFÉlino.
No full textEsta publicação tem como objetivo, promover a cafeicultura na Amazônia. O nosso Cafelino, é o personagem símbolo da cafeicultura moderna, com tecnologia, boa produtividade e rentabilidade. Ele vai nos contar a história do café e fornecer informações, ensinando aos pequenos agricultores como produzir o melhor café do mundo
Torque behavior of one-phase permanent magnet AC motor
No full textThis paper presents a detailed comparative study of two starting and running methods for a single-phase permanent magnet synchronous motor, equipped with a squirrel-cage rotor. The analysis of the motor performance is realized for a pulse width modulated (PWM) inverter fed motor and for a capacitor-start, capacitor-run motor. The developed approach may be extended to any 1-phase ac motor—induction, synchronous reluctance or synchronous permanent magnet
Estudo e otimização de conversores estáticos utilizados em sistemas fotovoltaicos conectados à rede elétrica comercial: Kleber César Alves Souza ; orientador, Denizar Cruz Martins
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-graduação em Engenharia Elétrica, Florianópolis, 2009Este trabalho apresenta um estudo na área de eletrônica de potência aplicada à tecnologia de painéis solares fotovoltaicos. Uma revisão das arquiteturas utilizadas até o momento para realizar a conversão de energia dos módulos fotovoltaicos é apresentada, além de uma breve classificação e evolução dos sistemas fotovoltaicos conectados à rede elétrica de energia. Para o trabalho, dois conversores CC-CC foram escolhidos, estudados e aplicados como estágios iniciais de potência a um sistema fotovoltaico conectado à rede elétrica. Estes foram projetados de tal maneira a levar em consideração a redução do número de componentes e das perdas. Uma estratégia de controle para os mesmos foi estudada e foi decidido que o controle associado ao primeiro estágio teria unicamente a função de forçar o mesmo a operar sempre próximo ao ponto de máxima potência. Um conversor CC-CA foi apresentado como segundo estágio do sistema. Uma análise detalhada do controle foi realizada e duas malhas de controle, trabalhando conjuntamente, foram empregadas. Uma para controlar a tensão contínua do barramento e o fluxo de potência. Outra para controlar a corrente de saída do sistema. Além disso, a pesquisa também considerou a possibilidade de conexão de cargas diretamente ao sistema, focando os esforços em cargas não-lineares. Um algoritmo seguidor de máxima potência foi apresentado além de um sistema de proteção e supervisão. Por fim, os resultados experimentais validam os estudos teóricos realizados, além de corroborar algumas hipóteses discutidas no decorrer do trabalho.This work presents a study on the application of power electronics in the photovoltaic system area. An overview of the power electronics architectures applied to photovoltaic modules energy conversion is presented, including a brief classification and evolution of grid connected photovoltaic systems. To the research, two DC-DC converters were chosen, designed and applied as first power stage of a grid connected system. They were designed considering the reduction of losses and devices. A control strategy for them was studied and it was decided that the control associated with the first stage would have only the function of forcing it to operate always near the point of maximum power. A DC-AC converter was presented as the second stage of the system. A detailed control analysis was developed and two loop controls, working together, were employed. One loop to control the voltage of bus and the power flow. Another to control the output current of the system. Moreover, the research also considered the possibility of connecting a load directly to the system, focusing efforts on non-linear loads. A maximum power point tracker algorithm and a system of protection and supervision were presented. Finally, the experimental results validate the theoretical studies conducted, in addition to corroborate some assumptions discussed in the course of work
AC/DC Characterization of a Ti/Au TES with Au/Bi Absorber for X-ray Detection
No full textTransition-edge sensors (TESs) are used as very sensitive thermometers in microcalorimeters aimed at detection of different wavelengths. In particular, for soft X-ray astrophysics, science goals require very high-resolution microcalorimeters which can be achieved with TESs coupled to suitable absorbers. For many applications, there is also need for a high number of pixels which typically requires multiplexing in the readout stage. Frequency-domain multiplexing (FDM) is a common scheme and is the baseline proposed for the ATHENA mission. FDM requires biasing the TES in AC at MHz frequencies. Recently, there has been reported degradation in performances under AC with respect to DC bias. In order to assess the performances of TESs to be used with FDM, it is thus of great interest to compare the performances of the same device both under AC bias and DC bias. This requires two different measurement set-ups with different processes for making the characterization. We report in this work the preliminary results of a single-pixel characterization performed on a TiAu TES under AC and afterwards under DC bias in different facilities. Extraction of dynamical parameters and noise performances are compared in both cases as a first stage for further AC/DC comparison of these devices.Accepted Author ManuscriptImPhys/Optic
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