61,294 research outputs found
Greenhouse AC-yhtyeen konsertti
No full textGreenhouse AC-yhtyeen konsertti Helsingissä, Bar Loosessa, Stupido Records levy-yhtiön 30 v. juhlissa
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
Recomendações para o enraizamento de estacas de acerola (Malpiguia glabra L.) nas condições climáticas de Rio Branco-Acre.
No full textCom o objetivo de se avaliar métodos alternativos para a produção de mudas de acerola, nas condições climáticas de Rio Branco-AC, o Centro de Pesquisa Agroflorestal do Acre (CPAF-Acre) desenvolveu estudos sobre o desempenho da espécie quanto ao enraizamento de estacas, em função da posição de retirada das mesmas no ramo
Feasibility of high-frequency alternating current power for motor auxiliary loads in vehicles
No full textThis paper presents a feasibility study into the application of a 100-V, 50-kHz high-frequency ac (HFAC) network for powering automotive electrical auxiliaries. The study is focused on motor-actuated loads and is divided into two sections. First, the investigation indicates the benefits of replacing low-torque dc motors with lighter and more efficient 400-Hz ac machines for applications such as electric fans, fuel pumps, or blower motors. A comparative examination of commercially available machines indicates space and weight reduction of more than 60%, and efficiency savings between 25% and 100% are possible. Second, the inquiry evaluates the viability of replacing existing dc/ac inverters with HFAC/ ac converters for high-torque ac machines as employed, for example, in electric- power-assisted steering (EPAS) or heating, ventilation, and air conditioning systems. Based on experimental and simulation results for a column-assist EPAS application employing a three-phase permanent-magnet synchronous motor, this paper shows that an HFAC drive is expected to reduce the voltage harmonic content below 50 kHz by at least 10% compared with the dc/ac inverter. However, the disadvantages of the former drive make it less attractive than the existing dc/ac circuit. Specifically, the EPAS motor torque ripple is expected to be approximately 2% higher compared with the dc counterpart drive. Further drawbacks of the HFAC/ac drive include high metal-oxide-semiconductor field-effect transistor (MOSFET) conduction losses, higher voltage harmonics above 50 kHz, and complex control requirements of the inverter. Conclusively, significant HFAC advantages for motor loads can only be attributed to machines with a nominal torque capability that is limited to 2 N ·m. However, given the number of such devices within a typical vehicle, this translates into a possible vehicle mass saving of 30 kg and a potential reduction in fuel consumption by 0.8 L/100 kmIEEE Transactions on Vehicular Technolog
Adiectis passim im margine Responsorum ac Constitutionum capitibus, ex quibus Author suam Epitomen compilauit ...
No full textA Bernardo à Rey, I. V. D. fideliter reddita, ac in Latinam linguam conuersa ; Adiectis passim im margine Responsorum ac Constitutionum capitibus, ex quibus Author suam Epitomen compilauit ...DruckermarkeImpressum im Kolophon: Lvgdvni, Excudebat Ioannes Pvllon, Alias De Trin, Impensis honesti uiri Pauli MirallietiAus dem Vorbesitz des Klosters Rheinau Exemplar der ZB Züric
Experimental studies of influence of DC and AC electric fields on bridging in contaminated transformer oil
No full textAnalysis of real operating condition revealed that HVDC transformers experience combined effect of DC biased AC electric field. The dynamics of pressboard particle in contaminated transformer oil under the influence of DC, AC and DC biased AC electric field has been investigated in this paper. Different levels of particle concentrations are tested at different applied voltages. Optical images of the particles accumulation together with conduction current have been recorded during the experiments. A complete bridge between the electrodes of cellulose particles were observed for all the tests carried out under DC and DC biased AC electric field. Opposite to that, for AC experiments, pressboard particles accumulated on surfaces of both electrodes but did not create a full bridge between the electrodes. It is concluded that a combination of DC and AC voltages in a HVDC transformer could lead to a bridge formation within the equipment which could cause failure
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
R v Ireland; R v Burstow [1998] AC 147, House of Lords
No full textEssential Cases: Criminal Law provides a bridge between course textbooks and key case judgments. This case document summarizes the facts and decision in R v Ireland; R v Burstow [1998] AC 147, House of Lords. The document also included supporting commentary from author Jonathan Herring.</p
AG Securities v Vaughan; Antoniades v Villiers [1990] 1 AC 417, House of Lords
No full textEssential Cases: Land Law provides a bridge between course textbooks and key case judgments. This case document summarizes the facts and decision in AG Securities v Vaughan; Antoniades v Villiers [1990] 1 AC 417, House of Lords. The document also includes supporting commentary from author Aruna Nair.</p
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