7,975 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
Wilbur Shaw, 1952 Junior
No full textWilbur Shaw was a junior at Jacksonville State Teachers College in 1951-1952.https://digitalcommons.jsu.edu/lib-ac-histimg/6046/thumbnail.jp
Larry Shaw, Student
No full textLarry Shaw was a student at Jacksonville State College (now Jacksonville State University) in the 1960s. (circa 1963)https://digitalcommons.jsu.edu/lib-ac-histimg/33952/thumbnail.jp
Wilbur Shaw, 1953 Senior
No full textWilbur Shaw was a senior at Jacksonville State Teachers College in 1952-1953. He was an elementary education major.https://digitalcommons.jsu.edu/lib-ac-histimg/4159/thumbnail.jp
Marvin Shaw, 1973-1974 Art Faculty
No full textMarvin Shaw was a member of the art faculty at Jacksonville State University in 1973-1974.https://digitalcommons.jsu.edu/lib-ac-histimg/45151/thumbnail.jp
Dataset for: The Effect of Organoclay Loading and Matrix Morphology on Charge Transport and Dielectric Breakdown in an Ethylene-based Polymer Blend
No full textDataset supports the publication: Shaw, A. V., Vaughan, A., & Andritsch, T. The effect of organoclay loading and matrix morphology on charge transport and dielectric breakdown in an ethylene-based polymer blend. Journal of Materials Science. Readme is contained within the spreadsheet.
Article abstract: The effect of an organoclay on the electrical properties of a polymeric host is described. The matrix was composed of a blend of high and low density polyethylene, such that a wide range of different morphologies could be generated, to which an ethylene/(vinyl acetate) copolymer was added, to increase compatibility between the organoclay and the matrix and, thereby, improve the organoclay dispersion. The ratio between the compatibiliser and organoclay was found to be important in forming a well-dispersed system, as evinced by thermogravimetric analysis, X-ray diffraction and scanning electron microscopy, indicating the effectiveness of the chosen compatibilisation strategy. DC conductivity was found to be determined by the precise distribution of the organoclay throughout the system; changes in morphology and phase structure of the matrix polymer resulting from changes in imposed thermal history had little effect per se, but varying degrees of self-assembly of the organoclay facilitated by different residence times within the quiescent melt could result in changes in overall DC conductivity of several orders of magnitude. Consequent increases in DC conductivity led to reductions in DC breakdown strength, implying failure through some avalanche or thermal process. However, a monotonic increase in observed AC breakdown strength implies that the associated underlying failure process is then very different.</span
Marvin Shaw, 1974-1975 Art Faculty 1
No full textMarvin Shaw was a member of the art faculty at Jacksonville State University in 1974-1975.https://digitalcommons.jsu.edu/lib-ac-histimg/48186/thumbnail.jp
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
Human rights journalism: advances in reporting distant humanitarian interventions
No full textDrawing on case studies of the reporting of distant humanitarian interventions, especially in Eastern Europe and Africa by the mainstream Western media, Ibrahim Shaw illuminates how journalists can create a more informed and empowered public sphere. He argues that journalists do not only hold the power to inform the public, but have the moral responsibility as duty bearers to educate and increase awareness of their rights and monitor, investigate and report all human rights violations. It is the first book to exclusively and critically explore the role of the media in the promotion and protection of human rights. Drawing on Kant's cosmopolitan principle of global justice, Shaw puts forward the case for human rights journalism as a more proactive approach in prioritising the deconstruction of indirect structural and cultural violence, and as the best way of preventing or minimising direct political violence
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