16 research outputs found
Space Charge Studies on Mid-voltage Cable by Thermally Stimulated Depolarization Currents in the Melting Temperature Range.
In the present work, a XLPE mid-voltage cable
from General Cable CO. has been studied by Thermally
stimulated depolarization currents. Systematic
measurements have been carried out in order to compare
the conductive processes in this cable with previous results.
Depolarization current as a function of thermal
annealing, thermal history, polarizing field and polarizing
time and temperature has been obtained. The results
show the presence of a broad and complex heteropolar
process between 60 and 120°C as expected. Annealing
of the sample at temperatures above SOT develops an homopolar
contribution associated to chemical components
diffused from the cable semiconducting layers into the
XLPE bulk. For annealing times of 60min at 140T and
2 days at 90°C, the homoplar current intensity reaches
a maximum, decreasing and recovering the heteropolar
sign with further annealing. Experiments performed with
different polarizing times and temperatures show as well
the presence of an homopolar contribution, overlapped
to the heteropolar behavior, that increases continuously
with polarizing time. These results indicate that conductive
processes within the XLPE are probably responsible
of homopolar charge injection
Annealing Effect on the Conductivity of XLPE Insulation in Power Cable
Conductivity () in XLPE insulation of power cables annealed at 90 ºC at
temperatures between 50 and 97 ºC has been measured. In all cases there is an initial
increase in conductivity that develops a maximum and finally decreases for long
annealing times. This maximum appears in the sample annealed 20 days when
conductivity is measured at 50 ºC and shifts gradually to higher annealing times up to
40 days when the measurement is performed at 97 ºC. A linear behavior of ln() versus
T -1/4 is observed, which implies that the transport mechanism is basically via thermally
assisted hopping conduction. Infrared spectroscopy indicates that, during annealing,
some chemical species diffuse from the semiconducting shields (SC) into the XLPE.
Thermally stimulated depolarization currents technique (TSDC) and intensity-current
measurements (I-V) point out as well the presence of this diffusion process that
becomes less significant after long annealing times. The initial increase in is
explained in terms of the increase in traps density due to the diffusion process from the
SC shields. Long term decrease in is justified by the observed decrease of diffusion
rate for long annealing times
Effect of annealing on conductivity in XLPE mid-voltage cable insulation
A new study of the electrical conductivity of crosslinked polyethylene (XLPE) mid-voltage (MV) cable insulation is presented. Its main
objective is to show the effect of annealing treatments on MV cables under actual service conditions. Complementary time domain
(absorption/resorption currents) and frequency domain (dynamic electrical analysis) techniques are applied on different laboratory
samples containing XLPE insulations: sections of XLPE insulated cable (with and without semiconducting screens) in the case of
absorption/resorption currents and, in the case of dynamic electrical analysis, a thin ribbon obtained from the cable insulation by
mechanical procedures. For annealing temperatures below a certain critical temperature, conductivity decreases both for XLPE cylinders
(cable sections from which inner and outer semiconducting screens have been removed) and for real cables (sections of cable with
semiconducting screens) but its value is smaller in the case of cables. If the annealing temperature is higher than the critical temperature,
the behaviour of conductivity is more complex. In XLPE, cylinders conductivity initially decreases with the annealing time but after some
annealing time it begins to increase, it passes over a maximum and eventually it decreases monotonically. In the case of real cable
sections, conductivity grows, tending to a saturation value, which is noticeably higher than the corresponding value of the maximum
obtained for XLPE cylinders. The experimental results are explained satisfactorily by means of the Mott equation that takes into account
hopping conduction assisted both by temperature and electric field
Personalized monitoring of electrical remodelling during atrial fibrillation progression via remote transmissions from implantable devices
Atrial electrical remodelling (AER) is a transitional period associated with the progression and long-term maintenance of atrial fibrillation (AF). We aimed to study the progression of AER in individual patients with implantable devices and AF episodes. Observational multicentre study (51 centres) including 4618 patients with implantable cardioverter-defibrillator and results þ/resynchronization therapy (ICD/CRT-D) and 352 patients (2 centres) with pacemakers (median follow-up: 3.4 years). Atrial activation rate (AAR) was quantified as the frequency of the dominant peak in the signal spectrum of AF episodes with atrial bipolar electrograms. Patients with complete progression of AER, from paroxysmal AF episodes to electrically remodelled persistent AF, were used to depict patient-specific AER slopes. A total of 34 712 AF tracings from 830 patients (87 with pacemakers) were suitable for the study. Complete progression of AER was documented in 216 patients (16 with pacemakers). Patients with persistent AF after completion of AER showed ∼30% faster AAR than patients with paroxysmal AF. The slope of AAR changes during AF progression revealed patient-specific patterns that correlated with the time-to-completion of AER (R = 0.85). Pacemaker patients were older than patients with ICD/CRT-Ds (78.3 vs. 67.2 year olds, respectively, P < 0.001) and had a shorter median time-to-completion of AER (24.9 vs. 93.5 days, respectively, P = 0.016). Remote transmissions in patients with ICD/CRT-D devices enabled the estimation of the time-to-completion of AER using the predicted slope of AAR changes from initiation to completion of electrical remodelling (R = 0.45). The AF progression shows patient-specific patterns of AER, which can be estimated using available remote-monitoring technology
Personalized monitoring of electrical remodelling during atrial fibrillation progression via remote transmissions from implantable devices
Aims: Atrial electrical remodelling (AER) is a transitional period associated with the progression and long-term maintenance of atrial fibrillation (AF). We aimed to study the progression of AER in individual patients with implantable devices and AF episodes. Methods and results: Observational multicentre study (51 centres) including 4618 patients with implantable cardioverter-defibrillator +/-resynchronization therapy (ICD/CRT-D) and 352 patients (2 centres) with pacemakers (median follow-up: 3.4 years). Atrial activation rate (AAR) was quantified as the frequency of the dominant peak in the signal spectrum of AF episodes with atrial bipolar electrograms. Patients with complete progression of AER, from paroxysmal AF episodes to electrically remodelled persistent AF, were used to depict patient-specific AER slopes. A total of 34 712 AF tracings from 830 patients (87 with pacemakers) were suitable for the study. Complete progression of AER was documented in 216 patients (16 with pacemakers). Patients with persistent AF after completion of AER showed ∼30% faster AAR than patients with paroxysmal AF. The slope of AAR changes during AF progression revealed patient-specific patterns that correlated with the time-to-completion of AER (R2 = 0.85). Pacemaker patients were older than patients with ICD/CRT-Ds (78.3 vs. 67.2 year olds, respectively, P < 0.001) and had a shorter median time-to-completion of AER (24.9 vs. 93.5 days, respectively, P = 0.016). Remote transmissions in patients with ICD/CRT-D devices enabled the estimation of the time-to-completion of AER using the predicted slope of AAR changes from initiation to completion of electrical remodelling (R2 = 0.45). Conclusion: The AF progression shows patient-specific patterns of AER, which can be estimated using available remote-monitoring technology
Exploring Health Science Students’ Notions on Organ Donation and Transplantation: A Multicenter Study
The knowledge acquired during university education about organ donation and transplantation (ODT) decisively influences the information future health professionals transmit. This is important in ODT where the participation of the general public is essential to obtain organs. Objective: To determine notions of Spanish medicine and nursing students on ODT and its relationship with attitude toward ODT. Methods and Design: and design. We conducted a sociologic, multicenter, and observational study. The population for our study consisted of medical and nursing students in Spanish universities. Our database was the Collaborative International Donor Project, stratified by geographic area and academic course. A validated questionnaire (PCID-DTO-RIOS) was self-administered and completed anonymously. Our sample consisted of 9598 medical and 10, 566 nursing students (99% confidence interval; precision of ±1%), stratified by geographic area and year of study. Results: The completion rate for our study was 90%. Only 20% (n=3640) of students thought their notions on ODT were good; 41% (n=7531) thought their notions were normal; 36% (n=6550) thought their notions were scarce. Comparing groups, there were differences between those who believed that their notions on ODT were good (44% nursing vs 56% medical students; P < .000), and those who believed it scarce (54% nursing vs 46% medical students; P < .000). Notions on ODT were related with attitude toward the donation of one''s own organs: those who considered their notions were good were more in favor then those who considered it scarce (88% vs 72%; P < .000). Conclusion: Only 20% of Spanish medical and nursing students thought their notions on ODT were good. Having good knowledge is related to a favorable attitude towards ODT. Receiving specific information on the subject could improve their knowledge about ODT during their training