bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of High Voltage Impulses on Surface Discharge at the Oil-Paper Interface
Authors: Clemence Kizza R , Ghaffarian Niasar M , Nikjoo R , Wang X , Edin H 
Published: February 2018

High voltage transients in electrical power systems are mainly caused by lightning strikes and switching operations. The high voltage transients above the basic insulation level (BIL) would degrade the electrical insulation of the equipment.In this work, the effect of high voltage impulses on the trend of the surface discharge at the oil-paper interface was investigated. The partial discharge patterns were recorded by the Insulation Condition Monitoring (ICM) system. The HV impulses were generated by a standard 1.2/50 μs HV impulse generator. The measurement results presented in this paper seem to show that surfacedischarge would cause complete breakdown (continuous flashovers) at the oil-paper interface much faster when the test sample is first aged by HV impulses comparedto when it is unaged.
Radial Flow Paths for Oil in Mass Impregnated HVDC Subsea Cables
Authors: Støa Bendik , Ildstad Erling , Runde Magne 
Published: February 2018

During temperature cycling the radial flow of oil, which is caused by differences in thermal expansion between the oil and paper, may lead to cavity formation in mass impregnated HVDC cables. Partial discharge activity in these voids is an important failure mechanism in this type of cable, but the governing processes are not fully established.This paper contributes to flow modeling through a literature survey and a comparison between two alternative flow patterns in the insulation. Only one detailed model of radial flow in this kind of insulation has been found in the literature. The model, which is based on porous media flow in a homogeneous insulation with constant porosity, and its suitability as a starting point for further modeling is reviewed.Two possible flow paths, radially outwards through the paper or between paper tapes from one layer to the next, have been considered. Based on previously unpublished experimental results, the flow resistance R of the two alternatives has been estimated. This quantity is found to be of the same order of magnitude in both cases, meaning that there probably will be flow both through and between the paper tapes.
Corona at Large Coated Electrodes
Authors: Larsson Mats , Hjortstam Olof , Faleke Håkan , Arevalo Liliana , Wu Dong , Ming Li 
Published: February 2018

In geometries relevant form HVDC applications where large electrodes and large air gaps are utilized, the observed corona can be quite different from geometries studied in the literature where needles or wires are used as high voltage electrodes. Corona discharges at large electrodes often initiates when the electric field on the electrode surface appears lower than the critical electric field strength, 2.4 kV/mm. Surface contamination of the electrode has been pointed out as the reason for such discharge events. Our experimental results indicate that one possible way to prevent such corona is to coat the electrode with an insulating material, such as epoxy or oxide layers. It seems that the layer separates any corona inducing particle from the electrode, which in turn hinders the corona to form. However, as the layer breaks down and gets punctured, the corona preventing propertied disappears and corona forms easily. We conclude that as long as the layer doesn’t get punctured, coating electrodes with insulating material is preventing corona to initiate at electrical fields below the critical electric field, as given by the electrode geometry. In contrast to positive polarity, for negative polarity the epoxy coating could withstand high electric fields without breaking down.
Estimating Transmission Line Parameters of Three-core Power Cables with Common Earth Screen
Authors: Li Yan , Wouters Peter A.A.F. , Wagenaars Paul , Van der Wielen Peter C.J.M. , Steenis Fred 
Published: February 2018

The propagation modes of travelling wave in a threecore power cable (XLPE or PILC) with common earth screen can be uncoupled into three modes: one shield to phase (SP) mode and two phase to phase (PP) modes. A generic model approach is applied in this paper to estimate the transmission line parameters of three-core cables with common earth screen, which includes the effect of different layers on series impedance and admittance. The characteristic impedance, the propagation velocity and the attenuation for SP and PP modes of two cable types, PILC and XLPE are modeled and compared with test results. Calculated parameters match within 5% for the characteristic impedances of different modes and 5% for the velocity for the PILC cable. Larger deviations occurred for XLPE cable, due to difficulties in appropriate modeling the semiconducting insulation screens around each conductor. The attenuation for both PILC and XLPE is hard to predict because data on complex permittivity, being the dominant factor, is hardly known.
Effects of Ambient Conditions on the Dielectric Properties of Thermally Sprayed Ceramic Coating
Authors: Niittymäki M , Rotthier B. , Lahti K. , Suhonen T. , Metsäjoki J 
Published: February 2018

Thermal spraying techniques are used to manufacture insulating coatings especially for demanding applications like fuel cells where normal insulating materials cannot be used. In electrical insulation applications, the mostly used coating materials are aluminum oxide (Al2O3), magnesium oxide (MgO) and magnesium aluminate (MgAl2O4). Dielectric properties of thermally sprayed ceramic coatings are strongly affected by ambient conditions, and in addition to this they are not well documented in the literature. In this paper the effects of environmental conditions on certain dielectric properties of a thermally sprayed coating are studied. DC resistivity as well as permittivity and losses at different frequencies at relative humidities of 20 % and 45 % at temperature of 20 °C, 40 °C and 60 °C will be reported in the paper for Al2O3 samples sprayed using HVOF (High Velocity Oxygen Fuel) technique. DC dielectric breakdown strength is also studied for the HVOF alumina coating at temperature of 20 °C and relative humidity of 20 %. Effects of ambient conditions and coating material composition are also analyzed.
Water Diffusion Barrier – A Novel Design for High Voltage Subsea Cables
Authors: Furuheim Knut Magne , Nilsson Susanne , Hvidsten Sverre , Hellesø Svein Magne 
Published: February 2018

High voltage subsea cables are normally sheathed with a metallic water barrier at voltage levels above 36 kV as recommended by the standards (IEC 60840). The main concern with water ingress in power cables is the risk of water tree formation. Water tree growth will reduce the lifetime of power cables. For dynamic cable designs there are today few reliable alternatives to prevent the water ingress. Here a novel electrical semi-conductive water barrier is presented, based on a multilayer polymer sheath design where the arrangement of layers is based on numerical simulations using measured water transport data.
Robustness Analysis of Classical High Voltage Joint Design Under High Voltage DC Stress
Authors: Fälth Fredrik , Kumar Santhosh , Ghorbani Hossein 
Published: February 2018

The demand for extruded HVDC cable systems for higher voltages has been increasing in different fields. This demand comes from the need for higher transmission capacity in applications such as integration of wind power, power system interconnectors and connection of offshore oil and gas platforms to land. Prefabricated joints are used to connect the cable delivery lengths. If badly designed, the possibility of breakdown in the joints is higher than in other parts of the system because of the number of interfaces and triple points between different materials. Due to the huge potential costs and the down-time imposed to the system in case of a joint failure, the robustness of the joints is of great importance. Two main approaches in the design of prefabricated joints for extruded cables exist in which the more recent one takes advantage of the nonlinear properties of modern field grading materials. In this work, we have examined the design challenges with focus on robustness issues in a 150 kV classical joint design without field grading material. The results show that with this approach, there are serious robustness issues which are challenging to overcome without field grading material.
Charge Decay Measurements on a Polymeric Insulation Material under Controlled Humidity Conditions
Authors: Späck Yvonne , Kumura Sarath , Gubanski Stanislaw 
Published: February 2018

In this work a systematic study on the influence of relative humidity on the charge decay of high-temperature-vulcanized flat silicone rubber samples is carried out by means of contactless measurements of the surface potential. Both virgin and aged (by a long-term corona treatment) samples were used for the experiments. Temporal and spatial variations of the potential were monitored during the charge decay process. The analysis of the results indicated that the charge decay becomes faster due
Dielectric Breakdown Strength of Polymer Nanocomposites-The Effect of Nanofiller Content
Authors: Takala Markus 
Published: February 2018

Insulation materials can be tailored by compounding nanofillers and polymer materials. The advantageous changes in properties of polymer nanocomposites can be explained by the large interface area of the nanofillers. Theoretical models developed in the field of nanodielectrics concentrate on the analysis of the interface volume.Dielectric breakdown strength (DBS) is one of the most important properties of an insulation material. The DBS of nanocomposites depends heavily on the nanofiller content and even small quantities can cause improvement. This is linked to the maximum interface volume achieved already at low nanofiller concentrations. Homogeneous nanodispersion is the key for DBS increase and reliable results. Often the most profitable nanofiller quantities are below 5 wt-%. The same kind of behaviour can be seen with different voltage shapes, but with dc voltage the increase is bigger. DBS has a maximum value with respect to nanofiller amount and decreases thereafter. Filler quantities around 5 wt-% and even lower are the most attractive considering DBS of nanocomposites.
Sensitivity Improvement of Acoustic Partial Discharge Detection Measurements through Wavelet Analysis
Authors: Evagorou Demetres , Janus Patrick , Niasar Mohamad Ghaffarian , Edin Hans 
Published: February 2018

Condition monitoring of power equipment is a vital stepin extending the lifetime of existing equipment andreducing costs for utilities while minimizing the risk ofunscheduled outages. Partial discharge (PD) monitoringhas evolved as a reliable mean of determiningdeterioration in insulation systems. Acoustic emissiondetection techniques are usually utilized for PDdetection mainly in oil-filled transformers offering theadvantage of being immune to electrical noise and amethod to localize PDs. In this work it was attempted toimprove the sensitivity of acoustic measurementsthrough wavelet analysis and estimation of the thresholdvalue from actual measurements of the noise, whichproved to be more effective compared to otherestimation values. The analysis was performed onlaboratory measurements from a 36 kV condenserbushing known to exhibit PD activity acquired with alow cost PD acoustic sensor developed at KTH. As anext step the results have to be verified by onlinemeasurements, which can result in the addition of anCondition monitoring of power equipment is a vital step in extending the lifetime of existing equipment and reducing costs for utilities while minimizing the risk of unscheduled outages. Partial discharge (PD) monitoring has evolved as a reliable mean of determining deterioration in insulation systems. Acoustic emission detection techniques are usually utilized for PD detection mainly in oil-filled transformers offering the advantage of being immune to electrical noise and a method to localize PDs. In this work it was attempted to improve the sensitivity of acoustic measurements through wavelet analysis and estimation of the threshold value from actual measurements of the noise, which proved to be more effective compared to other estimation values. The analysis was performed on laboratory measurements from a 36 kV condenser bushing known to exhibit PD activity acquired with a low cost PD acoustic sensor developed at KTH. As a next step the results have to be verified by online measurements, which can result in the addition of an onboard signal-processing box for improved sensitivity.
Influence of Applied Voltage and Temperature on the Current through the Alumina-filled poly(ethylene-co-butyl acrylate) Nanocomposites Under Constant Stress
Authors: Jaeverberg N , Venkatesulu B , Jonsson B.L.G. , Edin H 
Published: February 2018

The current through the poly(ethylene-co-butyl acrylate) with 13 wt% of butyl acrylate (EBA) filled with 6 wt% of alumina nanoparticles with an approximate diameter of 45 nm was studied under constant stress application. The particles were either unmodified or surface-treated with aminopropyltriethoxy silane. The current was measured either until breakdown or for maximum stress duration of 10 minutes. Two voltage levels were chosen: 15 and 22.5 kV, which were low enough not to cause a breakdown during the ramping of the voltage at the rate of 490 V/s to the constant voltage level at room temperature. Several ramping rates {100, 260, 500, 1007} V/s were also tested for the reference unfilled material to evaluate its influence on the time to breakdown. Several temperature levels were tried: 20 (room temperature), 40 and 50 ºC.As expected, higher applied voltage caused higher current through the materials, while higher temperature caused earlier breakdown as well as higher current. At the lower voltage level most of the materials survived the testing. At the higher voltage level most of the samples of the unfilled reference material failed at the temperatures above room temperature while most of the nanocomposite samples survived the testing even at higher temperatures.
Thickness Dependency in Dielectric Breakdown Strength of Biaxially Oriented Polypropylene-Silica Nanocomposite Films
Authors: Ranta Hannes , Rytöluoto Ilkka , Lahti Kari 
Published: February 2018

The power law relationship has been used to some extent in order to compare dielectric breakdown strength results between materials of varying thickness. However, especially in case of relatively new materials such as nanocomposites, it can be questioned whether the measured results actually behave accordingly to the power law and to what extent – most importantly, can the power law be used to predict properties of thinner films than those actually measured. This paper addresses the problem in case of biaxially oriented PPsilica nanocomposite films of different thickness, the breakdown results of which are compared and fitted to the power law relationship.
Capacitor performance limitations in high power converter applications
Authors: El-Khatib Walid Ziad , Holboell Joachim , Rasmussen Tonny W. 
Published: February 2018

High voltage low inductance capacitors are used in converters as HVDC-links, snubber circuits and sub model (MMC) capacitances. They facilitate the possibility of large peak currents under high frequent or transient voltage applications. On the other hand, using capacitors with larger equivalent series inductances include the risk of transient overvoltages, with a negative effect on life time and reliability of the capacitors. These allowable limits of such current and voltage peaks are decided by the ability of the converter components, including the capacitors, to withstand them over the expected life time. In this paper results are described from investigations on the electrical environment of these capacitors, including all the conditions they would be exposed to, thereby trying to find the tradeoffs needed to find a suitable capacitor. Different types of capacitors with the same voltage ratings and capacitances where investigated and compared a) on a component scale, characterizing the capacitors transient performance and b) as part of different converter applications, where the series inductance plays a role. In that way, better insight is achieved on how the capacitor construction can affect the total performance of the converter.
Correlation between serum Calcium levels and smear grading among the pulmonary tuberculosis patients
Authors: CHANDRA T. Jaya , SOWJANYA M. 
Published: February 2018

Objective: To find the serum calcium (Ca) levels in the pulmonary
tuberculosis (PT) patients and its correlation with smear grading.

Methods: Microscopically
confirmed PT patients were included in the test group and healthy individuals
in the control group. Two sputum samples were collected from the participants
by the same day approach. Smears were stained by Ziehl Neelsen staining
technique. Simultaneously 5 ml blood was collected; serum was separated by
centrifugation at 3000 rpm, 10 minutes. Serum Ca was estimated by kit method,
by auto analyzer. ANOVA test was used to find the statistical significance.

Results:
Total 100 participants were included. The mean serum Ca levels were 7.2 mg/dL
and 9.4 mg/dL in the test and control groups, respectively. Grade wise the mean
serum Ca levels were 7.4 mg/dL, 7.3 mg/dL, 7.1 mg/dL and 7 mg/dL respectively
for scanty, 1+. 2+ and 3+. Statistically the difference was not significant
among the groups and the grades.

Conclusion: As per our study hypocalcemia is observed in PT
patients and the mean serum Ca levels were decreased with smear grading. J Microbiol Infect Dis 2018; 8(1):19-22
Vitamin K2 in Managing Nocturnal Leg Cramps
Authors: Tan Jing , Zhu Rui , Li Ying , Wang Li , Liao Shigeng , Cheng Lin , Mao LingXiu , Jing Dan 
Published: October 2024

ImportanceCurrently, there are no treatments for nocturnal leg cramps (NLCs) that have been proven to be both safe and effective. Seeking safe and effective approaches for managing NLCs is of crucial importance.ObjectiveTo determine whether vitamin K2 is better than placebo in managing NLCs.Design, Setting, and ParticipantsThis multicenter, double-blind, placebo-controlled randomized clinical trial was conducted in China between September 2022 and December 2023. This study used a volunteer sample comprising community-dwelling individuals 65 years and older with 2 or more documented episodes of NLCs during 2 weeks of screening. Researchers performed a history and physical screening of candidates recruited from the community through advertisements, and eligible participants were randomized in a 1:1 ratio to receive vitamin K2 or a placebo for 8 weeks.InterventionsPatients orally took capsules containing either vitamin K2 (menaquinone 7), 180 μg, or a similar-looking placebo every day for 8 weeks. The study products were custom manufactured to have identical packaging and for the capsules to have matching appearance and identical excipients that shared similar taste and weight.Main Outcomes and MeasuresThe primary outcome was the mean number of NLCs per week between the vitamin K2 and the placebo group. Secondary outcomes included the duration of muscle cramps measured in minutes and the severity of muscle cramps assessed using an analog scale ranging from 1 to 10.ResultsAmong the 310 participants, 111 participants were excluded. Of the 199 enrolled individuals, 108 (54.3%) were female, and the mean (SD) age was 72.3 (5.5) years. A total of 103 patients (51.8%) were randomly assigned to receive vitamin K2 and 96 (48.2%) were assigned to placebo. The mean (SD) baseline weekly frequency of cramps was comparable in both the vitamin K2 group (2.60 [0.81]) and the placebo group (2.71 [0.80]). During the 8-week intervention, the vitamin K2 group experienced a reduction in the mean (SD) weekly frequency of cramps to 0.96 (1.41). Meanwhile, the placebo group maintained mean (SD) weekly frequency of cramps at 3.63 (2.20). The between-group difference was statistically significant (difference, −2.67; 95% CI, −2.86 to −2.49; P &amp;lt; .001). The vitamin K2 group had a more significant mean (SD) reduction in NLC severity (−2.55 [2.12] points) compared with the placebo group (−1.24 [1.16] points). The vitamin K2 group exhibited a more pronounced mean (SD) decrease in the duration of NLCs (−0.90 [0.88] minutes) than the placebo group (−0.32 [0.78] minutes). No adverse events related to vitamin K2 use were identified.Conclusions and RelevanceThis randomized clinical trial showed that vitamin K2 supplementation significantly reduced the frequency, intensity, and duration of NLCs in an older population with good safety.Trial RegistrationClinicalTrials.gov Identifier: NCT05547750
Prenatal Cannabis Exposure and Executive Function and Aggressive Behavior at Age 5 Years
Authors: Keim Sarah A. , Fried Peter , Yeates Keith Owen , Boone Kelly M. , Vrantsidis Daphne M. , Dean Abigail , Murnan Aaron W. , Rausch Joseph , Klebanoff Mark A. 
Published: October 2024

ImportanceCannabis use during pregnancy is increasingly common in the US and may affect the development and behavior of preschool-aged children.ObjectiveTo prospectively investigate the association of prenatal cannabis exposure with executive function and aggressive behavior at age 5 years.Design, Setting, ParticipantsThis cohort study was conducted from 2016 through 2020. Data analysis was conducted from 2022 through 2024. Patients aged 16 through 50 years who were able to communicate in English and intended to deliver at the Ohio State University Wexner Medical Center were enrolled in a pregnancy research repository. Participants (n = 355) who gave consent for future contact and whose child(ren) was presumed to be alive were invited to participate again at child age 5 years (children born May 25, 2010, through February 7, 2016) and 250 children participated (70%).ExposureCannabis exposure was measured prospectively by urine toxicology, maternal self-report, and obstetric record abstraction.Main Outcomes and MeasuresExecutive function and aggressive behavior, measured via multimodal assessment by staff masked to exposure status. Outcomes were chosen a priori.ResultsOf 250 children, 80 were exposed to cannabis (32%). Use of tobacco, other drugs, and alcohol during pregnancy was common (22% to 39% each). Most families were living in poverty. There were 155 children who were Black/African American, non-Hispanic (62%); 11 were Hispanic (4%); 34 indicated more than one race or another race, non-Hispanic (14%); and 50 were White, non-Hispanic (20%). Age-corrected standard scores for children’s attention and inhibitory control (National Institutes of Health Toolbox) were about 0.4 SDs lower for those exposed to cannabis compared with unexposed (β = −6.1 points; 95% CI, −10.8 to −1.4), following propensity score weighting and adjustment for confounders. Exposed children also exhibited poorer task-based planning ability and more observed aggression. Caregiver ratings of executive function and behavior and laboratory assessments of other aspects of executive functioning showed no differences by exposure status.Conclusions and RelevanceResults from this contemporary US cohort where prenatal cannabis exposure was common and indicated that exposed children exhibited some differences in aspects of executive function and behavior relevant to long-term academic success and adaptive functioning. These results may be considered in refining clinical recommendations regarding cannabis use during pregnancy.