97,738 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
Rail Condition Monitoring using Axle Box Acceleration Measurements: Defect detection in the Netherlands and Romania
No full textIn this paper we discuss rail condition monitoring based on axle box acceleration (ABA) measurements. We present three case studies. The first one in The Netherlands, the detection of local defects with different severity levels (squat A, squat B and squat C) is analysed. The second case from the Faurei testing ring in Romania, the detection of rail defects over the whole testing ring is presented and examples of responses at a local defect (wheel-burn) is discussed with measurements at 80km/h (conventional speed measurement) and 200km/h (high speed measurement). In the third case, ABA measurements were obtained during operation in a train with passengers in the railway line near Brasov, Bartolomeu-Zărneşti. Examples of the defects and validations are discussed.Railway Engineerin
Practical application of on-line partial discharge monitoring technique on 500kV shunt reactor
No full textConsidering the damage mechanism of oil-impregnated paper insulation in power transformers, shunt reactors and other high voltage electrical apparatus caused by partial discharge, a concept of “destructive partial discharge” is introduced in this paper. The intensity of this discharge is regarded as several thousands pico-coulomb (pC) and may cause the insulation a fatal damage. An oil-paper insulation is usually able to withstand this type of partial discharge for a period of time prior to failure. This provides engineers a time window to detect it. This paper describes an on-line partial discharge monitoring system for 500kV shunt reactors. The commission results from 3 single-phase shunt reactors either connected or disconnected to the grid showed that the on-line partial discharge detecting system has a high noise immunising ability. Two years later after the installation, a pre-warning signal was received from one shunt reactor indicating the existence of an intermittent discharge. The acoustic emission system located its position at the low end of the high voltage bushing in the oil. Dissolved gasses analysis (DGA) in the oil suggested the presence of partial discharge, as acetylene (C2H2) was as high as 20ppm. PD activity was further confirmed by a physical examination on the reactor
Aquatica Fu, Ballantyne et Lambkin 2010
No full textAquatica Fu, Ballantyne et Lambkin 2010 Figs 54, 55, 56 Aquatica Fu Ballantyne et Lambkin 2010: 1, figs 2–49. Yiu 2012: 56–59; 2017: 87. Fu 2014: 69 − 82. Type species. Aquatica wuhana Fu et al. 2010. Diagnosis. Known from China. Usually found near bodies of water, including rice paddies, as associated larvae are aquatic and bottom dwellers, having soft bodies and forked lateral gills and spiracles, along the sides of the body. Adults of Aquatica Fu et al. usually have dark brown to black elytra with orange yellow pronotum; several species have dark brown elytra narrowly pale margined, and may have a median dark mark on the pronotum; one species has pale yellowish brown dorsum. Larvae are presently indistinguishable from larvae of Luciola cruciata and L. owadai. Adult males of Aquatica are distinguished from these two species of Luciola by the nature of the elytral epipleuron and the outline of the aedeagal sheath sternite margins. When a horizontal specimen is viewed from beneath, the base of the epipleuron in the two Luciola species is not much expanded and the elytral humerus is clearly visible. In Aquatica species the epipleuron is sufficiently expanded at its base that in a similar orientation the humerus is not visible from beneath. This genus belongs to a group of 18 Luciolinae genera where in the male aedeagus the LL are visible from beneath at the sides of the ML. It has the posterior portion of the male aedeagal sheath sternite emarginated on its right side in common with 10 other genera (Atyphella, Aquilonia, Convexa, Emeia, Lloydiella, Missimia, Pacifica, Pygatyphella, Sclerotia and Triangulara), from which it is distinguished by having posterior half of sternite irregularly emarginate along both sides, and each side toothed. It is distinguished from Abscondita by having the aedeagal LL separate along most of their dorsal length (those of Abscondita are fused); from Asymmetricata by the symmetrical T8 (that of Asymmetricata is emarginated on its right side); from Curtos in lacking the characteristic elytral punctation and raised humeral carina; and from Pygoluciola by the shape of the aedeagal sheath (that of Pygoluciola has a symmetrical sternite with a narrow anterior half which expands posteriorly and is not emarginated at either side). Females are macropterous and the bursa has narrowed paired plates in several species. Remarks. Fu (2014: 49) identified as ‘ Luciola sp.’ specimens subsequently been identified as a new species of this genus and which will be described elsewhere (Fu, Oba, Ballantyne in prep.). Nak-eiam (2015) also identified this same species from Thailand but did not describe it. Yiu (2012) identified both Aq. leii and Aq. ficta from Hong Kong, and discussed the possibility that L. ficta could be a junior synonym of L. limbalis Fairmaire. He also indicated (2017) that two males and five females had been taken in Hong Kong. Fu & Meyer-Rochow (2012: 127) studied morphological adaptations of larval leii. Fu et al. (2007, 2009) addressed eversible defensive larval organs of several species of Aquatica. Fu (2014) illustrated the glowing light organs of male and female pupae of Aq. ficta (fig. 73) and Aq. leii (fig. 77).Published as part of Ho, - Z., 2019, The Luciolinae of S. E. Asia and the Australopacific region: a revisionary checklist (Coleoptera: Lampyridae) including description of three new genera and 13 new species, pp. 1-174 in Zootaxa 4687 (1) on page 43, DOI: 10.11646/zootaxa.4687.1.1, http://zenodo.org/record/350809
Space charge characteristics of multi-layer oil-paper insulation under different DC voltages
No full textIn this paper, space charge in oil-paper insulation system has been investigated using the pulsed electroacoustic (PEA) technique. A series of measurements were carried out when the insulation system was subjected to different applied voltages. Charge dynamics in the insulation system during the volts-on, volts-off and decay have been analyzed. It has been found that homocharge injection occurred both at the anode and the cathode. Positive charges are observed to accumulate in the layers, which indicate that the oil-paper layer interfaces act as a barrier for positive charges. The decay tests showed that after 30min, about a quarter of space charges remained in the sample, about 90% charges disappeared after 2 hours. Finally, total charge variation in these tests were analyzed
Feasibility study of on-line monitor of cable oversheath
No full textA circuit model has been proposed to represent an underground power cable system and its surroundings. The damage on oversheath is represented by a resistive component. The simulations on different parameters were carried out using PSpice to examine the change in the detecting branches brought by this resistive component. The simulated results indicate that it is possible to detect the damage by monitoring the current change at each joint bay. When there is a fault on oversheath of the cable the current drifts away from its normal value. By monitoring the branch current shape change at adjacent joint bays it is possible to locate the fault. However, the accuracy of the modelling depends on the values of parameters used
Spectroscopic and photometric behaviour of the FU Orionis variable Z Canis Majoris?
No full textAbstract. We present optical and IR photometry, optical multi-dispersion spectroscopy, and IR spectrophotometry of the FU Ori variable Z Canis Majoris, obtained in th
Photometric variability in FU Ori and Z CMa as observed by MOST
No full textPublisher's Version/PDFPhotometric observations obtained by the MOST satellite were used to characterize optical small-scale variability of the young stars FU Ori and Z CMa. Wavelet analysis for FU Ori reveals the possible existence of several 2–9 d quasi-periodic features occurring nearly simultaneously; they may be interpreted as plasma parcels or other localized disc heterogeneities revolving at different Keplerian radii in the accretion disc. Their periods may shorten slowly which may be due to spiralling in of individual parcels towards the inner disc radius, estimated at 4.8 ± 0.2 R☉. Analysis of additional multicolour data confirms the previously obtained relation between variations in the B − V colour index and the V magnitude. In contrast to the FU Ori results, the oscillation spectrum of Z CMa does not reveal any periodicities with the wavelet spectrum possibly dominated by outburst of the Herbig Be component.</p
The Benefits of Being Economics Professor A (and not Z)
No full textAlphabetic name ordering on multi-authored academic papers, which is the convention in the economics discipline and various other disciplines, is to the advantage of people whose last name initials are placed early in the alphabet. As it turns out, Professor A, who has been a first author more often than Professor Z, will have published more articles and experienced afaster growth rate over the course of her career as a result of reputation and visibility. Moreover, authors know that name ordering matters and indeed take ordering seriously: Several characteristics of an author group composition determine the decision to deviate from the default alphabetic name order to a significant extent.performance measurement, incentives, economists, name ordering
The Semantic Web - {ISWC} 2020 - 19th International Semantic Web Conference, Athens, Greece, November 2-6, 2020, Proceedings, Part {II}
No full textThe Semantic Web - {ISWC} 2020 - 19th International Semantic Web Conference, Athens, Greece, November 2-6, 2020, Proceedings, Part {II
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