PD detection and localization by means of acoustic measurements onhydrogenerator stator bars

Acoustic partial discharge detection appears useful for the location of PD sources within various kinds of insulating systems. The usefulness of such a method to locate discharge sources in hydrogenerator stator bars is illustrated. The adopted measuring procedure, based on two piezo-electric transducers positioned on a bar, allows the identification of the discharge site position within an error range of ~2 cm. Such a measuring procedure appears useful as a diagnostic tool in quality control for bars that do not pass the specified acceptance test or in the development of new insulating systems. The measurement circuit and the relevant test procedure are presented. Further comments about the measured acoustic velocities of the acquired signals are given     

Medium term aging characterization of enamelled for high frequency applications

This work is related to a medium term research program which aims at studying the behaviour of twisted pair specimens of enamelled copper wires subjected to high frequency sinusoidal voltage waveforms which are used in some advanced types of electrical machines. High frequency voltages due to, for instance, converter operation are not considered in this paper. The following test conditions were adopted: different voltage amplitudes up to 2 kV, selected voltage frequencies up to 5 kHz and test temperatures up to 200 /spl deg/C. The experimental work aims at defining reference-testing procedures and at studying the aging process of enamelled wires which are usually employed in random windings of electrical machines. As final result, a phenomenological model of the aging process, acting in the considered insulation system, is obtained and it is accurately defined on the grounds of the output data. The type of test method adopted and the type of data processing appear worthy to be used in order to characterize enamelled wires in terms of thermoelectrical degradation processes in presence of partial discharges.     

Synthesis and Properties of New Cleavable Cationic Surfactants Containing Carbonate Groups

A novel series of cleavable alkyltrimethylammonium surfactants with different hydrocarbon chain lengths (C8–16) were synthesized. A carbonate break site inserted between the polar head and the hydrocarbon chain makes these compounds hydrolyzable. The reagents used are renewable, (bio)degradable, or reusable. The hydrolysis of these cleavable surfactants will lead to the generation of fatty alcohols and choline, which is an essential biological nutrient. The surface activities in aqueous solution of the synthesized carbonates fulfill the requirement of being good surfactants. In addition, the cleavable compounds containing n-decyl and n-dodecyl chains showed similar or higher antimicrobial activities when compared to a non-cleavable analog.     

Influence of aging on electrical properties of polyethylenenaphthalate-2,6 dicarboxylate films

Poly(ethylene naphthalate 2,6 dicarboxylate), thanks to its heat resistance, may be used as insulating material in motors and laminated chip capacitors. In these specific applications the occurrence of partial or corona discharges leads to insulation aging and possible breakdown. An experimental investigation has been carried out to determine the changes in dielectric properties as function of the aging conditions, e.g. the temperature of irradiation. Dielectric loss values have been determined in the 10² to 10⁶ Hz frequency range from 150 to 200°C. Three relaxation peaks were found α,β*,β, in the order of decreasing temperature     

Aging diagnosis of insulation systems by PD measurements.Extraction of partial discharge features in electrical treeing

The charge height values associated with PD measured during electrical tree inception and growth are processed according to the Weibull distribution. Test arrangements, based on the needle-plane electrode system, consider specimens having either a cavity at the tip or an intimate contact with insulation. It is shown that the Weibull-function parameters have close relation to discharges occurring in cavity and tree channels, and that an indication of inception of electrical trees can be obtained     

Dielectric properties of epoxy/montmorillonite nanocomposites and nanostructured epoxy/SiO2/Montmorillonite Microcomposites

Composites reinforced with microparticles using a polymer matrix reinforced by nanoparticles represent a new emerging class of materials. Epoxy composites have been prepared using quartz as microfillers and organically modified Montmorillonite as nanofillers in order to study the dielectric properties of such new materials. The structure of the composites as determined by transmission electron microscopy, is neither exfoliated nor intercalated, although the thickness of C30B stacks is in the nanometric range. The influence of nano‐ and microparticles on epoxy matrix amorphous structure has been highlighted through Differential Scanning Calorimetry experiments. C30B has not effect on glass transition temperature but a drastic from 357 K to 325 K decrease is observed with the addition of microparticles. Heat capacity step remains unchanged, except for the microcomposite. And finally, Broadband Dielectric Spectroscopy has been used to characterize the dielectric properties at different temperatures. The spectra have been fitted with Havriliak–Negami equation to extract the relaxation times and the dielectric strengths associated with local β and γ relaxations and the main α relaxation. POLYM. COMPOS., 115–124, 2016. © 2014 Society of Plastics Engineers     

Thermomechanical and electrical characterization of epoxy‐organoclay nanocomposites

The effect of amount of clay content on the thermomechanical and electrical properties of epoxy/organoclay nanocomposites is investigated in the present research. An organoclay, cloisite 30B (C30B), was dispersed in the epoxy resin and was cured with an amine curing agent. The morphology of the nanocomposite examined by X‐ray diffraction shows exfoliation for nanocomposites with lesser clay content and intercalation for nanocomposites with higher clay content. The storage modulus (E′) of the nanocomposites increases monotonously with the increase in the amount of clay. The short time alternating current breakdown strength of the nanocomposites increases by the addition of C30B up to a certain clay content and then show a decrease. The space charge measured by pulsed electroacoustic method shows that the nanocomposite accumulate a very less amount of space charge and the charge decay in the nanocomposites are quicker than in the pure polymer. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Do whole-body vibrations affect spatial hearing?

To assist the human operator, modern auditory interfaces increasingly rely on sound spatialisation to display auditory information and warning signals. However, we often operate in environments that apply vibrations to the whole body, e.g. when driving a vehicle. Here, we report three experiments investigating the effect of sinusoidal vibrations along the vertical axis on spatial hearing. The first was a free-field, narrow-band noise localisation experiment with 5- Hz vibration at 0.88 ms^? 2. The other experiments used headphone-based sound lateralisation tasks. Experiment 2 investigated the effect of vibration frequency (4 vs. 8 Hz) at two different magnitudes (0.83 vs. 1.65 ms^? 2) on a left–right discrimination one-interval forced-choice task. Experiment 3 assessed the effect on a two-interval forced-choice location discrimination task with respect to the central and two peripheral reference locations. In spite of the broad range of methods, none of the experiments show a reliable effect of whole-body vibrations on localisation performance.