115 research outputs found
Dataset for 'The Dielectric Effect of Xylene on an Organoclay-Containing Composite'
No full textThe dataset supports the journal paper Shaw, A. V., Vaughan, A., & Andritsch, T. (2018). The Dielectric Effect of Xylene on an Organoclay-Containing Composite. IEEE Transactions on Dielectrics & Electrical Insulation.
These data were collected in addition to the data collected for the conference paper submitted in July 2018 with the same title. This journal paper combines some work from the conference paper with additional work to form a journal article. </span
The effect of water on the dielectric properties of polypropylene/aluminium nitride nanocomposites
No full textA series of aluminium nitride/polypropylene nanocomposites were prepared. Nano aluminium nitride was surface functionalised by silane coupling agents with different hydrolysable groups and the effect of the surface chemistry and preconditioning (i.e., under different relative humidity) on their AC breakdown strength and the DC conductivity was investigated. The effect of water on the nanosilica-based nanocomposites have been studied by many researchers and the dramatically decreased AC breakdown strength and DC resistivity for wet samples were reported[1, 2]. By contrast, aluminium nitride filler with less hydrophilic sites, hydroxyl groups, was applied in this study. Furthermore, octyl silanes were adopted and the displacement of hydroxyl groups to short carbon chain on the particle surface is expected.The preconditioning results show that the silane functionalisation can effectively reduce the amount of water absorbed during 15 days of immersion in deionized water. The dielectric properties show a high dependency on the sample preconditioning and water content. The DC conductivity of the non-treated aluminium nitride/polypropylene nanocomposites is 2 orders of magnitude higher than the octyl functionalised silane. Similar behaviour was observed on the AC breakdown data. However, the difference between systems treated with silane coupling agent with different hydrolysable groups cannot be seen from the weight monitoring and dielectric properties mentioned above. Although the dielectric results in [3] show the different hydrolysable groups might bring different bonding structure between nanoparticle and silane coupling agents, the interaction with water seems to have less dependency on it.In this study, It can be concluded that the nanoparticle surface chemistry is very important in determining the macroscopic properties, especially in a humid environment. The surface functionalisation by silane coupling agent can effectively minimise the hydrophobicity of nanocomposites.[1] D Qiang, Y Wang, G Chen, and T. Andritsch, "Influence of Water Absorption on Space Charge Behavior of Epoxy Nanocomposites," 2016.[2] I. Hosier, M. Praeger, A. Holt, A. Vaughan, and S. Swingler, "On the effect of functionalizer chain length and water content in polyethylene/silica nanocomposites: Part I—Dielectric properties and breakdown strength," IEEE Transactions on Dielectrics and Electrical Insulation, vol. 24, no. 3, pp. 1698-1707, 2017.[3] X. Wang, T. Andritsch, and G. Chen, "Effect of Surface Functionalization on the Dielectric Properties of Polypropylene Aluminium Nitride Nanocomposites," in 2018 IEEE 2nd International Conference on Dielectrics (ICD), 2018, pp. 1-4: IEEE
Epoxy Based Nanodielectrics for High Voltage DC Applications: Synthesis, Dielectric Properties and Space Charge Dynamics
No full textMain goal of the research described in this PhD thesis was to determine the influences of filler size, material and distribution on the DC breakdown strength, permittivity and space charge behaviour of nanocomposites. This should lay the groundwork for tailored insulation materials for HVDC applications. Examples for this are medical and industrial X-ray imaging, radar and cable terminations. In the course of this project a manufacturing process was devised, which enabled the fabrication of epoxy based nanocomposites with a good dispersion of different types of nanoparticles. Models from literature, which explain the behaviour nanodielectrics exhibit, are discussed: electric double-layer model, intensity model, multi-core model and the interphase volume model. Based on these theories, a new model was devised for explaining the behaviour of epoxy based nanocomposites: the polymer chain alignment model. The underlying idea of this model is that the restructuring of the base polymer on the molecular scale, due to the presence of surface modified nanoparticles, plays a fundamental part in the properties of the bulk material. Each modified particle will act as centre for crosslinking of the polymer, leading to a rigid layer of polymer chains around each particle. These rigid layers have a much lower permittivity than both host and filler material, thus their presence can easily be identified by dielectric spectroscopy, since the relative permittivity of the bulk material decreases. In literature it is shown, that the strong bonding of particles and host material due to the surface modification gives rise to improved resistance to partial discharges and electrical treeing. More energy is needed to break these bonds than it would be the case in unmodified polymers. The particles themselves can also act as recombination centres for electrons and holes, which travel between or along polymer chains. This has an effect on the space charge dynamics. Agglomerations of nanoparticles can nullify these effects however: it is explained how agglomerations can act as charge traps, lead to field enhancements and cause interfacial polarization. Claims from theory are tested with three measurement methods: short term DC breakdown tests, dielectric spectroscopy and space charge measurement. It is shown that nanocomposites exhibit improved DC breakdown strength for very low fillgrades of 0.5 to 2 % by weight. Compared to the unmodified base material improvements of up to 80 % could be measured. Dielectric spectroscopy reveals that the relative permittivity in nanocomposites is lower than of the host and filler materials, with a minimum at a fillgrade of approximately 2 % by weight. For higher fillgrades the permittivity of the composite increases depending on the ratio between the permittivity values of filler and host material. Above 2 wt.% the permittivity of the filler material starts to overshadow the low permittivity of the rigid layers around the particles. Results from space charge measurement with the pulsed electro-acoustic method show that the quality of particle dispersion has an impact on the charge intake. Based on these measurements it is concluded that particle agglomerations act as charge traps, while the amount of charges in nanocomposites with good particle dispersion is lower than in the unmodified epoxy. This confirms that the particles indeed act as recombination centres, actively mitigating charge buildup inside the material. These results show why nanocomposites are very interesting for HVDC equipment. Space charges are a limiting factor for DC applications. Their reduction improves the reliability of the insulation system. The increased DC breakdown strength enables more compact high voltage equipment, respectively the utilization at higher field strengths. The work presented here is a stepping stone on the way to industrial applications of nanostructured insulation material and fundament for further investigations on topics like nanofluids.Electrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
The effect of material processing on the dielectric properties of polystyrene boron nitride nanocomposites
No full textExtensive experimental work in the area of polymer nanocomposites has been done over the past two decades to explore their potential. In this study, a range of related polymer nanocomposite materials was prepared using a solvent blending method, using dichloromethane (DCM), toluene (TOL) and chlorobenzene (CB) to dissolve the polymer, atactic polystyrene (a-PS), and disperse the filler, hexagonal boron nitride (hBN). Where TOL and CB were used, heat was used in material processing, whereas the material was processed at room temperature with DCM. The largest increase in breakdown strength is observed in the materials processed with TOL and CB. The hBN appears to be well dispersed in these systems and more agglomerated in the DCM system as shown from SEM
On the influence of chemical defects and structural factors on charge transport and failure in polyethylene
No full textA blend of high and low density polyethylene was aged at 160 °C in air and the impact of the chosen aging protocol on local chemistry, crystallinity and charge transport dynamics was considered. The aging conditions were chosen in order to exploit oxygen diffusion effects, such that the resulting systems could be considered as bi-layer specimens, containing two regions: a uniform lightly aged layer and a more spatially varying highly aged layer, which vary in the concentrations of aging-related defects such as carbonyl groups and unsaturation. For aging periods up to 3 h, little space charge was found within both the highly and lightly aged layers. However, after aging for about 3.5 h, an abrupt change in behavior was observed, whereby charges move rapidly through the highly aged layer, accumulating at the interface with the lightly aged layer. Sample melting behavior, as determined by differential scanning calorimetry, was found to depend on aging time, as a result of impeded crystallization and retarded reorganization kinetics. We suggest that this abrupt change in charge transport behavior is a consequence of the local concentration of chemically related trapping sites exceeding some critical threshold. The consequence of the resulting space charge distribution is a dramatic increase in the local electric field across the lightly aged layer and a consequent reduction in the overall DC breakdown strength. However, while further aging exacerbates these space charge effects, counter to expectations, the breakdown strength then recovers somewhat, suggesting a change in the underlying mechanism of electrical failure
Electrical breakdown strength of boron nitride polyethylene nanocomposites
No full textThere is a growing demand for the design of high-performance insulators for high voltage applications. It was proposed that the addition of nanofillers to a polymer could potentially enhance the electrical properties of insulators when compared to the conventional unfilled or microfilled polymers [1]. These materials have captured the interest of many researchers worldwide since then, as present dielectric materials could benefit from improvements in properties such as dielectric strength, dielectric loss, electrical and thermal conductivity, and permittivity that nanodielectrics offer. However, many of the underlying principles remain uncertain, such as the polymer/nanofiller interface, and researchers are still exploring solutions to common challenges faced by nanodielectrics such as nanoparticle agglomeration [2].The work presented in this paper is based on a hexagonal boron nitride nanocomposite in a polyethylene blend host polymer. A polyethylene blend composed of 80% low density polyethylene (LDPE) and 20% high density polyethylene (HDPE) is chosen as the polymer matrix since it has a higher electrical breakdown strength than pure LDPE. Hexagonal boron nitride was chosen as a nanofiller because of its attractive properties for high voltage applications such as high dielectric strength, high thermal conductivity, and mechanical robustness [3]. A solution blending method is used to mix the nanoparticles in the polymer as better quality materials and nanoparticle dispersion are achieved.This paper will investigate the AC electrical breakdown behaviour of the prepared polymer nanocomposite materials. The electrical breakdown strength of the unfilled polymer will be compared to the untreated hexagonal boron nitride filled polymer at different loading levels. The addition of this nanofiller is expected to alter the dielectric strength due to changes in the material’s structure. The chemical structure of hexagonal boron nitride is illustrated in Figure 1, where there is an equal number boron and nitrogen atoms firmly bound together. The breakdown results will then be analysed using a two-parameter Weibull distributio
Impact of particle thermal treatment on dielectric properties of core-shell filled epoxy nano-composites
No full textThis paper presents the effect of Silica-Titania (SiO2@TiO2) core-shell nano-particles added into amine-cured epoxy composites, under three different particle treatment conditions: untreated, calcined at 250 ∘C and 450 ∘C , on the dielectric and structural properties of the bulk composite. Characterization was conducted using a range of methods Transmission Electron Microscopy (TEM), Fourier Transform Infra-Red Spectroscopy (FTIR), Raman Spectroscopy, Differential Scanning Calorimetry (DSC) and Broadband Dielectric Spectroscopy (BDS). TEM confirmed the synthesis of the core-shell architecture with denser shells at higher calcination temperatures. Raman spectroscopy showed an increase in the Ti-O-Ti network formation and orderliness with elevated temperature treatment. Incorporating untreated filler into epoxy reduces the bulk real permittivity, while the inclusion of calcined fillers leads to an increase. An additional ω relaxation was observed in imaginary permittivity spectra of nano-composites pointing towards altered molecular dynamics within the epoxy due to nano-particle addition. These findings highlight the role of core-shell nano-particles in modifying the dielectric properties of epoxy composites, whilst differentiating them from conventional nano-particles
The effect of exfoliation on the breakdown strength of polystyrene boron nitride composites
No full textResearch on polymer nanocomposites promises to create a new class of materials with enhanced dielectric properties. This paper reports on the study of polystyrene systems filled with hexagonal boron nitride (BN) nanoparticles. The polymer nanocomposite materials were produced using a solvent blending procedure, where some of the materials were produced using dichloromethane (DCM) as the solvent and others using isopropyl alcohol (IPA). The breakdown strength was measured at different loading levels; the breakdown strength was found to decrease at the 5 wt% loading level, but increased again with 10 wt% and higher loadings of BN. The effect of exfoliation by solvent choice and sonication on the breakdown strength was investigated; sonication in IPA produced the best results. However, micrographs obtained from the scanning electron microscope show no apparent change of the dispersion of BN in the sonicated systems with the different solvents
Nanodielectrics-examples of preparation and microstructure
No full textThe main problem for nanocomposite synthesis is still to achieve a good dispersion and distribution of nanoparticles in the host material. In most cases this requires surface treatment of the filler material to improve compatibility with the usually dissimilar host material. Besides the fillgrade, particle type, size, aspect ratio, and surface modification all alter the properties of a nanocomposite. The synthesis method itself also has an effect on the microstructure and, therefore, dielectric behavior of nanocomposites. Finally, it is important to control all variables and minimize moisture ingress during preparation and processing of nanodielectrics, since contaminants and moisture degrade the dielectric properties of nanocomposites considerably. © 2013/IEEE
The prospects and challenges for HVDC cable technology in a smart grid world
No full textHigh voltage direct current (HVDC) cable systems are traditionally the best solution for long-distance submarine transmission, but are not very common on land. However, the improved performance of AC/DC converters, in terms of cost and power throughput, and public concerns for the environmental and visual impact of overhead lines, are making HVDC cable technology more and more appealing. Indeed, it is generally believed that the increasing penetration of HVDC cable transmission will make the world grid smarter, fostering flexibility, reliability, and sustainability by integration of renewables, which are often far away from load centers. This has led to a near exponential growth of HVDC cable lines worldwide in the past two decades
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