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Insulator leakage current is the primary root cause of pole fires; therefore, it is critical to recognize outdoor insulators as potential cause of wildfires. [ABSTRACT FROM AUTHOR]

In this paper, the dependence of XLPE electrical breakdown on carrier mobility controlled by both electric field and temperature is evaluated by simulations and experiments. The molecular chain displacement model incorporating the thermoelectric effect of carrier mobility is examined to elucidate the experimental results. Trapping and de-trapping characteristics of space charge and mobility dynamics are modeled using hopping and Poole-Frenkel mechanisms. The experimental outcomes reveal that the DC electrical breakdown reduces with corresponding increment in temperature and thickness. Trapping parameters are estimated from experiments for simulations. The DC breakdown strength from experiments represents an inverse power relation with both the insulation thickness and temperature. The simulation results of molecular chain model with hopping mobility express more permanence with experimental results in comparison with Poole-Frenkel mobility. [ABSTRACT FROM AUTHOR]

This paper presents the surface modification and charge transportation mechanism of thin polyimide films. Here, we demonstrate that the surface modification of these films, by using the fluorine gas-phase, improves the charges mitigation and, thereafter, suppress the space charges. The experimental results indicate that the thermal step current for fluorine coated films reduce significantly in comparison to pure polyimide films. The thin layer of fluorine coating helps to release the surface charge, reduce the charge injection from the electrode, provide hindrance for charges to penetrate into the bulk of the films and the higher degree of charge disappearing helps to reduce the space charge growth. [ABSTRACT FROM AUTHOR]

This paper describes a polyimide (PI)/nanocomposite multilayer 3D model design on the basis of actual boundary conditions attained from SEM images of synthesized films. The impact of nanoparticle dispersion on the electric field enhancement is explicitly described in the model. The electrical properties of these synthesized multilayer PI/nanocomposite films are also measured through experimental results. The results expose that the chances of nanoparticles dispersion are improved by pasting a thin PI/nanocomposite layer on both sides of PI film as compared to the single layer of PI/nanocomposite film. In consequence, less space charge and low electrical fields are observed in multilayer films. Our methods will help to reliably predict the dielectric strength of polymer/nanocomposite insulating materials. Additionally, the new synthesized multilayer PI/nanocomposite insulating material will ensure reliable operation for electric motors and increase its lifespan. [ABSTRACT FROM AUTHOR]

In this study, XLPE electrical breakdown depending on insulation thickness is analyzed by simulations and experiments. The bipolar space charge and molecular chain displacement models are investigated to explain the experimental results. The results from experiments indicate that the electrical DC breakdown field decreases with increasing insulation thickness. For simulations, carrier mobility and trapping parameters are obtained from experiments. The simulation results of both models present an inverse power relationship between the DC breakdown strength and insulation thickness. The simulation results of molecular chain mobility model show consistency with experimental results as compared to a bipolar space charge model. The movement of polymer chain containing deep traps expands the free volume and this enlargement in free volume can be a major reason for the variation in the DC electrical breakdown strength of XLPE with insulation thickness. [ABSTRACT FROM AUTHOR]

The enhancement of DC breakdown strength in polypropylene/alumina nanocomposites (NCs) with low filler content (1 wt%) while the obviously increased partial discharge (PD) resistance at higher filler content (15 and 20 wt%), are observed. Possible mechanisms underlying such contrastive performance are proposed based on considering a combination of electric conductivity, traps distribution and morphology of the eroded test specimen. The DC breakdown is closely related to trap-controlled charge transport and the property is improved for NCs with low filler content. Comparatively, the PD resistance of NCs with higher filler content exhibits longer failure time and more spreading of the eroded area on specimen surface. A model of PD resistance of NCs is proposed on the basis of synergistic effects of energy dissipation by nanoparticle scattering and charge dissipation. The scattering effect on charged ions induced by nanoparticles plays an important role in energy dissipation, and faster charge dissipation along the sample surface induced by shallower traps mitigates energy concentration. Thus two aspects contribute to the improved PD resistance. It is concluded that the effects of nanofillers on short-term DC breakdown and long-term PD resistance are different. A low filler content improves short-term DC breakdown performance whereas a high filler content enhances long-term PD resistance. [ABSTRACT FROM AUTHOR]

Silicone rubber is a hydrophobic polymer which is widely employed for high voltage outdoor insulation. The material offers excellent electrical performance under contaminated environments. However, pristine silicone rubber has low thermal properties and this may cause tracking and erosion failure due to severe dry band arcing and ohmic heating on the insulating surface. This work investigates the effect of material thermal characteristics on the tracking and erosion resistance of silicone rubber filled with micron sized alumina tri-hydrate (ATH), aluminum nitride (AlN) and boron nitride (BN) particles. Composites with different loading were synthesized by dispersing particles in pristine room temperature vulcanizing (RTV) silicone rubber and IEC 60587 inclined plane test (IPT) was conducted to evaluate tracking and erosion resistance. Apart from physical parameters and leakage current, an infrared thermal imager was used to measure the surface temperature distribution during the course of IPT. Experimental results showed tracking and erosion resistance is significantly enhanced with addition of BN particles followed by ATH. AlN composites exhibit poor tracking and erosion resistance, similar to pristine silicone rubber. It is concluded that addition of BN-composites improves ability to impede the tracking and erosion process, the reasons being better thermal stability and enhanced thermal conduction in the discharge region. On the other hand, infrared analysis revealed thermal accumulation is remarkably higher in AlN-composites which promotes dry band arcing and results in tracking and erosion failure. [ABSTRACT FROM AUTHOR]

Surface flashover properties should meet stringent requirements for the use in electrical equipment under high voltage DC environments. With the aim of enhancing surface flashover properties and understanding the mechanisms involved at ambient conditions, epoxy nanocomposites with different weight proportions of nano-TiO2 were prepared. A silane coupling agent was selected to functionalize the TiO2, the effect of which on nanoparticles dispersion and distribution was perused through scanning electron microscopy and infrared spectroscopy. DC surface flashover measurements in five normally used ambient conditions (N2, air, CO2, SF6 and vacuum) were conducted and results were analyzed relating to loading content, gas parameters, surface trap parameters as well as electrical conductivity of nanocomposites. Outcomes indicate that with low content of nanoparticles, the density of deep traps was increased, showing a positive effect on inhibiting surface flashover. When the nanoparticle content is higher than 1 wt%, the overlapped transitional region reduced the energy level of traps, resulting in a poor display of surface flashover voltages. It was found that the nanoparticle content had a greater influence on surface flashover in vacuum. Electron negativity, ionization coefficient and mean free path of gases were taken into account to explain why surface flashover in SF6 appeared to be the highest, whereas in N2, it was the lowest. At last, effects of gas-solid interactions on surface flashover combining surface-trap characteristics, secondary electron-emission contributions and gas molecule impact-ionization characteristics were analyzed. [ABSTRACT FROM AUTHOR]

Exposure to corona discharge damages the polymeric structure of alumina trihydrate (ATH) filled silicone rubber composite insulators. In this work, an attempt has been made to enhance the resistance against sustained long term corona exposure of ATH filled silicone rubber by fabricating its co-filled composites through addition of a small amount of nano Al2O3. Fabricated specimens comprise a pristine sample of silicone rubber (SR), one micro 40wt% ATH (MSR) composite and two co-filled 39wt% ATH+1wt% nano Al2O3 (MSR1%) and 38wt% ATH+2wt% nano Al2O3 (MSR2%) composites with total particle loading of 40wt%. They are subjected to AC corona exposure produced from a needle electrode tip for seven days. Performance evaluation is achieved through SEM (Scanning electron microscopy), FTIR (Fourier transform infrared spectroscopy), hydrophobicity, and surface roughness. Test results show severe material ruptures occurred in SR but damage in the form of pits and voids in MSR and MSR1% in the area directly below the needle tip. Interestingly, MSR2% exhibits subdued damage and a compact lump structure. The hydrophobicity recovery rate is significantly higher below the needle tip than in the vicinity, and in the SR as compared to the other composites. Also noted is higher increment in average and peak surface roughness below needle tip, and strong resistance to roughness increment by MSR2%. FTIR results show higher concentration of hydroxylation and aluminum nitrites in MSR and the absorbance intensities of principal functional groups show fewer deviations in MSR1% and MSR2% relative to their virgin states. Based on experimental results, it is concluded that corona resistance of micro ATH filled silicone rubber can be enhanced through addition of small amount of Al2O3 by fabrication of co-filled composites. [ABSTRACT FROM PUBLISHER]

Outdoor insulators are often subject to corona discharges and the problem is becoming more prevalent with the increasing use of higher transmission voltage levels. For polymeric insulators, exposure to such discharges can alter the chemical structure of basic polymer and degrade surface properties. This paper investigates the effect of micro and/or nano fillers in silicone rubber composites in suppressing such damage. Four different types of samples are fabricated: pristine silicone rubber (PR), 30wt% micron?sized silica/silicone rubber (MC), 27.5wt% micron + 2.5wt% nano silica/silicone rubber (NMC), and 5wt% nano silica/silicone rubber (NC) composites. Samples are exposed to AC corona using a needle to ground-plane electrode setup. Experimental results are analyzed based on five different measurement methods: phase-resolved partial discharge (PD), hydrophobicity loss-recovery, Scanning Electron Microscopy (SEM), Surface roughness and Fourier Transform Infrared Spectroscopy (FTIR). Results indicate that NC shows a strong resistance to partial discharges and hydrophobicity loss. In the area below the needle tip, higher hydrophobicity loss and higher recovery are observed as compared to the vicinity region. Variations in surface roughness, appearance of crackles, voids, pits, surface splitting into blocky structures and damages to chemical structure of silicone rubber are appreciably retarded in NC as compared to PR, MC and NMC. Based on NMC results, it is found that addition of nano?sized silica can be an attractive approach to improve the corona resistance of micron?sized silica filled silicone rubber. [ABSTRACT FROM PUBLISHER]