194 research outputs found
Data for 'On the influence of morphology and chemical defects on change transport dynamics in polyethylene: thermal ageing and concentration gradient'
No full textThis dataset supports the publication:
Somyot Tantipattarakul, Alun S. Vaughan and Thomas Andritsch
On the influence of morphology and chemical defects on change transport dynamics in polyethylene: thermal ageing and concentration gradient
Journal of Physics D: Applied Physics
DOI:10.1088/1361-6463/ab2f38</span
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
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 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
Additive manufacturing – understanding the implications and opportunities of novel manufacturing techniques on the electrical power sector
No full textDielectric, thermal and mechanical properties of polypropylene/ultra‒high molecular weight polyethylene nanocomposites for power cables
No full textCross‒linked polyethylene (XLPE), which is the current state of the art insulation system for HV cable systems, is difficult to recycle due to its crosslinked, thus thermoset, nature. In efforts of achieving more sustainable cable systems over the complete lifecycle of the asset, alternative insulation systems have been investigated. One major limitation for XLPE in terms of the thermal stability, thus maximum operating temperature, is the fact that the base polymer for XLPE systems, branched low‒density PE, has an inherently low melting point. As a consequence, even after cross‒linking, the resulting compound undergoes a softening transition around the temperature the base polymer would melt but is held together by the cross‒links. A replacement for PE should have an inherently higher melting point, which, if high enough, could mean that a cross‒linker would not necessarily be required. This would make the material easier to recycle by design.Further, the material needs to be cheap in bulk, easy to process and thus compatible with extrusion processes common in the HV cable sector, have a low loss and dielectric constant, and have adequate thermal conductivity. Polypropylene (PP) fits many of these requirements. However, PP without any additives is too brittle to be used in HV cables, and the thermal conductivity of PP is significantly lower than that of PE‒based compounds, which means that the increased thermal headroom by virtue of a higher melting point is rather restricted.Present work shows the effects of surface‒modified magnesium oxide (MgO) nanofillers on the AC breakdown strength, thermal conductivity, and mechanical properties of PP, as well as composites with ultra‒high molecular weight polyethylene (UHMWPE). If UHMWPE is mixed in with PP, the resulting polymers show separate crystallisation peaks, signifying insufficient miscibility. When MgO nanoparticles are mixed in, the composites move from separate crystallisation to co‒crystallisation peaks, which suggests that the addition of the nanofiller improves the miscibility by acting as a compatibilizer. The UHMWPE improves thermal conductivity from 0.21 W/m∙K to 0.31 W/m∙K due to its long molecular chains. Mechanical elasticity of PP/UHMWPE blends is enhanced due to the weak bonding strength at the interfaces resulting from the incompatibility between PP and UHMWPE. The addition of MgO improves bonding between the otherwise separate PP and UHMWPE phases, further improving the mechanical and dielectric breakdown strength of these blends. While the AC breakdown strength drops for PP/UHMWPE blends, the addition of nanoscale MgO not only recovers but slightly improves breakdown strength values
Modification of polypropylene-based cable insulation material
No full textPolypropylene (PP) is one of the recyclable and ease processed thermoplastics，and it expected used as the cable insulation material to reply the unrecoverable material crosslinked polyethylene(XLPE). However, isotactic polypropylene which is too stiff with a lower electrical character cannot be directly used into the high voltage cable insulation system. In this paper, several polymers have been blended with polypropylene to improve the properties of the PP blend samples. Electrical and mechanical experiments of the modifying PP blends will also be done. In accordance with the experimental results, blends of PP and propylene-ethylene copolymers (PEC) are potentially more suitable for modifying PP in HV insulation
Evaluation of the effect of moisture on dielectric properties of ester liquids
No full textFour different types of insulation liquids have been investigated: synthetic ester MIDEL 7131, natural esters MIDEL 1204, MIDEL 1215, as well as Nytro Gemini X mineral oil as reference material. The liquids were subjected to different humidity conditions (32% and 75% respectively) and subsequently characterized by means of AC breakdown, DC conductivity, dielectric spectroscopy (for permittivity and loss tangent) as well as KF titration. The effect of moisture on the loss tangent was minimal in ester liquids, even when saturated, while the temperature dependence of esters was more pronounced than that of mineral oil. The expectation was that synthetic esters would show improved AC breakdown results, but this was not the case. Natural ester MIDEL 1215 showed the best breakdown strength, also outperforming the mineral oil, while the synthetic ester had significantly reduced Weibull scale and shape parameters. Contrary to expectations, natural ester MIDEL 1215 performed significantly better than the synthetic ester in terms of AC breakdown strength and temperature dependence of conductivity and loss factor. Synthetic ester was also found to be much more dependent on moisture content than the natural ester
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