213,622 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
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
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
Pharmacoeconomic analysis of adjuvant oral capecitabine vs intravenous 5-FU/LV in Dukes' C colon cancer: the X-ACT trial
No full textOral capecitabine (Xeloda<sup>®</sup>) is an effective drug with favourable safety in adjuvant and metastatic colorectal cancer. Oxaliplatin-based therapy is becoming standard for Dukes' C colon cancer in patients suitable for combination therapy, but is not yet approved by the UK National Institute for Health and Clinical Excellence (NICE) in the adjuvant setting. Adjuvant capecitabine is at least as effective as 5-fluorouracil/leucovorin (5-FU/LV), with significant superiority in relapse-free survival and a trend towards improved disease-free and overall survival. We assessed the cost-effectiveness of adjuvant capecitabine from payer (UK National Health Service (NHS)) and societal perspectives. We used clinical trial data and published sources to estimate incremental direct and societal costs and gains in quality-adjusted life months (QALMs). Acquisition costs were higher for capecitabine than 5-FU/LV, but higher 5-FU/LV administration costs resulted in 57% lower chemotherapy costs for capecitabine. Capecitabine vs 5-FU/LV-associated adverse events required fewer medications and hospitalisations (cost savings £3653). Societal costs, including patient travel/time costs, were reduced by >75% with capecitabine vs 5-FU/LV (cost savings £1318), with lifetime gain in QALMs of 9 months. Medical resource utilisation is significantly decreased with capecitabine vs 5-FU/LV, with cost savings to the NHS and society. Capecitabine is also projected to increase life expectancy vs 5-FU/LV. Cost savings and better outcomes make capecitabine a preferred adjuvant therapy for Dukes' C colon cancer. This pharmacoeconomic analysis strongly supports replacing 5-FU/LV with capecitabine in the adjuvant treatment of colon cancer in the UK
Mutation frequencies following the 5-FU-, 4NQO-, and CPT-treatment.
No full textA), C), and E) The frequencies of overall Lys+ mutations following treatments with 5-FU (10 μM), CPT (100 μM), or 4NQO (0.2 μg/mL), respectively, for 24 hrs. B), D), and F) The frequencies of the uracil-dependent A>C and T>G mutations following treatments with 5-FU, CPT and 4NQO, respectively. Error bars indicate 95% confidence intervals. The number of cultures used to determine the frequencies of mutations and the numerical values of the median mutation frequencies and the confidence intervals represented as graphs in this figure are listed in S4 Table.</p
DS_10.1177_0022034519893672 – Supplemental material for Mdm2 Promotes Odontoblast-like Differentiation by Ubiquitinating Dlx3 and p53
No full textSupplemental material, DS_10.1177_0022034519893672 for Mdm2 Promotes Odontoblast-like Differentiation by Ubiquitinating Dlx3 and p53 by H. Zheng, G. Yang, J. Fu, Z. Chen and G. Yuan in Journal of Dental Research</p
sj-docx-1-jdr-10.1177_00220345221077202 – Supplemental material for Dlx3 Ubiquitination by Nuclear Mdm2 Is Essential for Dentinogenesis in Mice
No full textSupplemental material, sj-docx-1-jdr-10.1177_00220345221077202 for Dlx3 Ubiquitination by Nuclear Mdm2 Is Essential for Dentinogenesis in Mice by H. Zheng, J. Fu, Z. Chen, G. Yang and G. Yuan in Journal of Dental Research</p
ac aging and space charge characteristics in low-density polyethylene polymeric insulation
No full textSpace charge characteristic in polymeric insulating materials under ac conditions is one of the areas receiving growing interests over the last few years. Following the establishment of several techniques that allow space charge under dc conditions to be characterised non-destructively, there is a continuous effort to apply the same techniques to ac conditions. Earlier results revealed that there was charge accumulation at very low frequency (<0.01 Hz) while the charge formation at high frequency was negligible especially at power frequency. These results gave the impression that space charge effect under ac conditions is not an issue to be concerned with despite new evidences emerging slowly indicate the effect of space charge on electrical deterioration of the insulating polymers. 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 under various electric stress levels at 50 Hz for various times at ambient temperature, however, the bulk work was carried out on the samples aged at 50 kV/mm. Space charge dynamics in the samples after ageing were monitored using the pulsed electroacoustic (PEA) technique. The results indicate that there is a significant amount of negative charge accumulation in the aged sample due to charge injection at high ageing stress. The amount of charge in the aged sample is related to the electric stress. Little amount of charge is present at low fields and accumulated charge increases rapidly once the applied field is greater than 10 kV/mm. Due to a very slow charge decay rate, it is believed that the injected charges are captured by the deep traps that may be formed during ac ageing. At 50 kV/mm, the total amount of charge increases with the ageing time initially and then levels off. It was also found that the amount of charge in aged samples is related to the electrode material. Little charge was observed when gold electrodes were sputtered on both side of the sample. The charge dynamics of the aged samples under dc bias differ from the sample without ac ageing, indicating changes brought in by ac ageing. Chemical analysis by infrared spectroscope (FTIR) and Raman microscope reveals no significant chemical changes taken place in the bulk of the material after ac ageing. Finally the consequence of the accumulation of space charge under ac conditions on the lifetime of the material has been discussed
Electric field determination of polymeric dc power cable in the presence of space charge
No full textSpace charge in polymeric power cables has been previously measured by the pulsed electroacoustic (PEA) technique and its influence on electric field distribution has been estimated assuming that the conductivity is independent of electric field. In this paper we proposed a method of determining electric field distribution considering the influence of the effect of electric field on the conductivity. The cable insulation is divided into thin layers with different conductivities and space charge present in the each layer is viewed as the consequence caused by difference in conductivity. Based on the hopping conduction mechanisms, it is possible to compute electric field distribution across the cable insulation. Compared with the electric field distribution without considering change in conductivity, the new proposed method shows reduction at the maximum electric field. However, the position of the maximum electric field shifts depending on space charge distribution
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