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In the dielectric and electrical insulation research field, phenomena at interfaces between different substances are important issues. To promote innovative research activities, especially in industries, collaborations among researchers with different types of expertise are essential. An application engineer of measurement systems can work as an interface of different research fields and contribute...
Electrical cable systems in nuclear power plants may be exposed to environmental stresses including elevated temperatures and gamma radiation. Over time this exposure can lead to degradation of cable insulation and jacketing. Prediction of long-term cable material performance has been based on results of short-term accelerated laboratory aging studies, but questions remain regarding the correlation...
Excessive heat generation and occurrence of partial discharge have been observed in end-turn stress grading (SG) system in form-wound machines under PWM voltage. In this paper, multi-winding stress grading (SG) system is proposed as a method to change resistance of SG per length. Although the maximum field at the edge of stator and CAT are in a trade-off relationship, analytical results suggest that...
Measurements of “dark currents” in pressurized SF6 in high uniform electric field are carried out. To identify the mechanism involved, the influences of electric field, gas pressure and relative humidity are investigated. The experimental results support the hypothesis of emission of charged water clusters from electrodes. A simple model describing the above mechanism is developed, which allows accounting...
In recent years, there is an increasing interest in applying natural esters as the alternative to mineral oils in large power transformers. But the low resistance to oxidation/gelling process poses a challenge for applying natural esters in free-breathing transformers. Some previous studies presented the gelling/oxidation behaviour of natural esters in terms of physical and chemical properties. There...
The developed DC space-charge life model has been used to investigate the effect of trap cross-sections and trapped charges on the aging process in polymers. The experiment was performed using a two-dimensional grid that consists of multiple squares with micro dimensions that are treated as isolated regions. This grid was used to represent the evolution of damage structures during the aging process...
By using the Finite Element Method (FEM), calculation techniques of electric field distribution for AC, DC voltages and DC polarity reversal conditions were developed in oil-pressboard (PB) composite insulation systems. By using PB layered models under HVDC conditions, it was recognized, the electric field distributions were remarkably controlled by PB arrangement in oil. In particular, it was clarified...
A quantum dot (QD) model for coated nano-particles was proposed for electronic transport phenomena appearing in polymer nanocomposites elsewhere (ICD Montpellier) in 2016. This model also applies to explain permittivity characteristics appearing in polymer nanocomposites such as reduced permittivity in a certain condition and to predict permittivity in high electric fields that reflects space charge...
Nanofluids are acknowledged as promising alternative for conventional insulation liquids. Recently researches herald the superb characteristics of reinforced nanofluids, thus this kind of smart fluids are a new concept, which will have a significant impact on the insulating fluid industry. Nevertheless huge steps need to be taken to realize applications of this innovative concept for industrial scale...
Low-density Polyethylene (LDPE) was modified by using simultaneously 2 additives. Each additive had a specific attribute. Silicon was used. Using TEM with EELS, it was proved first that the passivated version constituted a double core consisting of Si surrounded by a nanometric layer of amorphous Silica (SiO2). Thus Si brought the possibility of an enlarged dielectric storage capacity with a barrier...
One challenge in studying nanodielectric composites is to produce reliable, reproducible samples. A common strategy to suppress aggregation and make the particles more compatible with the polymer matrix is to modify the nanoparticle surface chemistry but, often, evaluation of the effectiveness of the chosen surface functionalization process can prove difficult. In this paper the emphasis is on feasible...
The permittivity, dielectric loss, and DC dielectric breakdown strength of additively manufactured, solvent-cast, and commercial polyimide films are reported As expected, commercial films performed better than both AM and solvent-cast lab-made films. Solvent-cast films generally performed better than AM films, although performance depended on the optimization of the material for the specific deposition...
In order to study the effect of space charge on oil flow electrification under DC voltage, an experimental model with plane electrode was designed. A closed oil circulating system was built to simulate the oil path between the windings inside a converter transformer. The results reveal that polarity of streaming current depends on the sample configuration. If the high voltage electrode was covered,...
Mineral oil is an excellent dielectric liquid with high coolant capability and low cost, playing important roles as both insulators and coolant liquid in oil-immersed power transformer. However, its flash point is too low, and it is poorly biodegradable once the oil spills or leakage occurs. In this work, pressboards impregnated by mixed oil containing pure mineral oil (80 vol%) and vegetable oil...
Carrier mobilities in polymeric insulators strongly depend on the morphology of the system. In this study, in order to achieve a comprehensive understanding of hole transfer in PE, we evaluate the hole mobility in amorphous polyethylene (PE) without any ad hoc parameters. We developed a multi-scale computational approach that consists of molecular dynamics simulations, quantum chemical calculations,...
It is known that both, physico-chemical surface modification and thermal treatment, can lead to enhanced electret properties of dielectric polymers. To further investigate the influence of surface modifications on charge storage in polypropylene (PP) electrets, a combined thermal and chemical treatment with orthophosphoric acid (H3PO4) is applied to PP films. Charged samples are then studied by means...
In the 2014 Whitehead Memorial Lecture, a straight-forward charge-spring model was introduced and shown to yield estimates for the piezoelectric thickness coefficients of ferroelectric polymers such as polyvinylidene fluoride (PVDF) and of polymer ferroelectrets such as cellular polypropylene or tubular-channel fluoroethylene-propylene copolymer systems. It was, however, observed that the predictions...
Ferroelectrets (also called piezoelectrets) are non-polar polymer foams or polymer systems with internally charged cavities. The charging process represents a series of dielectric barrier discharges (DBDs), and is critical for the piezoelectric properties of ferroelectrets. DBD charging relies on the breakdown of the gas molecules, and therefore strongly depends on the gas components inside the cavities...
Dielectric properties can be described using a double well potential model where charges fluctuate thermally activated between the minima. The transition rates of the charges depend on the temperature, on the barrier heights within the double wells and on the local field at the double wells. The polarization P depends on these transition rates. We extend this model by introducing interactions between...
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