Isaias Ramirez

Erosion resistance and mechanical properties of silicone nanocomposite insulation

The results of erosion resistance, tensile strength, elongation at break, hardness, and thermal stability measurements are presented for silicone nanocomposites prepared using various nano and micro silica and alumina fillers in a two-part silicone rubber (SiR) matrix. The fillers are used to improve the erosion resistance of SiR, which is necessary for outdoor insulation housing applications. Good dispersion of the fillers is achieved using Triton/sup TM/, a common surfactant. An optimal surfactant concentration imparts good erosion resistance to the nanocomposites in laser heating tests without adverse effects, but excess surfactant has a negative impact on the mechanical properties of the silicone. Thermal gravimetric analysis demonstrated that nano fumed silica imparts better heat resistance to silicone than natural nano silica or nano alumina fillers. Fourier transform infrared spectroscopy analysis of the nanofillers indicated a significantly higher concentration of silanol groups in the nano fumed silica filler than in micro silica. The influence of the increased number of silanol groups on the erosion resistance of the nanocomposites and their mechanical properties is discussed.

Nanofilled silicone dielectrics prepared with surfactant for outdoor insulation applications

This paper reports on the heat erosion resistance of various silicone rubber compositions under infrared laser heating that simulates the dry band arcing phenomenon on outdoor insulation. The composites are made using a two-part addition cure silicone rubber, with various amounts of alumina, natural silica, or fumed silica, nano-or micron size, and different amounts of Tritontrade X-100 surfactant. It is shown that the surfactant greatly improves the dispersion of nanosized particles, yielding composites that are more homogeneous, with improved resistance to heat ablation. Significantly improved dispersion in the presence of surfactant is confirmed by SEM analysis for some nanofillers, while very little effect is observed for others. The surfactant is beneficial up to the point where the filler surface is saturated with the additive. Fumed silica is shown to impart greater heat ablation resistance than natural silica and alumina. Furthermore, a distinct protection mechanism appears to be operative for fumed silica and natural silica as opposed to alumina.

Measurement of leakage current for monitoring the performance of outdoor insulators in polluted environments

Monitoring of leakage currents on various types of insulators, in the field and in laboratory tests, has provided a much broader perspective on the performance of outdoor insulators in various pollution zones. The technique can be effective for corrective maintenance of transmission lines, provided the type of pollutant and the critical leakage currents are analyzed periodically. A leakage current that is continuous, periodic, or increasing with time is one consideration in the performance of insulators in pollution zones, whereas the maximum permissible levels of leakage current at flashover, which is considerably different for each insulator profile, is another consideration. What this means is that insulators showing lower leakage currents will not necessarily have the best operating performance. The insulator profile affects the accumulation of pollutants, which defines their pollution performance, and control of the leakage current by the insulator design depends largely on the type of pollutant. As a result, there is no unique solution, and leakage current values with flashover risk from laboratory tests for various types of insulators must be determined by using the type of pollutant in the field. This combination of strategies will provide an effective means of ensuring reliable transmission line operation in pollution zones.

Performance of silicone rubber nanocomposites in salt-fog, inclined plane, and laser ablation tests

This paper explores how the addition of inorganic nanofiller and microfiller to silicone rubber can impart resistance to erosion for overhead insulation applications. Various micro-nano composites were prepared for this study, namely microfiller, nanofiller, and the combination of microfiller and nanofiller with a commercial surfactant to improve the dispersion of the nanofiller. The effect of the surfactant on the surface wettability of the composites was analyzed with contact angle measurements. Salt-fog, inclined plane and laser ablation tests were conducted to evaluate the erosion resistance of the micro-nano filled composites. The results in all three tests showed that the combination of microfiller and nanofiller with surfactant resulted in composites with improved erosion resistance to dry band arcing, with the exception of the case where calcinated filler was used in the formulation.

Comparison of the erosion resistance of silicone rubber and EPDM composites filled with micro silica and ATH

The paper presents the results of inclined plane tests on ATH and silica composites of Silicone rubber (SiR) and EPDM to evaluate the effect of filler type and loading on the tracking and erosion resistance of the composites formed. The effect of test voltage on the outcome of the incline plane was also examined. A laser ablation test was also used to evaluate the various composites. A critical test voltage of 4.5 kV was shown to cause failures in samples which emphasizes the importance of testing composites at voltages above this critical level. In comparing the two test methods, both the inclined plane and laser ablation test methods showed the same order for EPDM composites of ATH and silica while the laser method showed silica SiR composites to perform somewhat better than in the inclined plane test which showed similar results.

Silicone rubber nanocomposites for outdoor insulation applications

The paper presents results on eroded mass measurements for nanofilled silicone rubber by controlled infrared laser heating, which simulates hot spot heating by dry-band arcing on wet and polluted composite insulators. Improvement in dispersion by surface treatment of the nanofillers with surfactants and by calcination is demonstrated. Along with improved dispersion of the nanofillers, a significant reduction in eroded mass is found in silicone rubber samples containing Tritontrade X-100 and treated fumed silica filler. Furthermore, the variations in eroded mass among the samples are also shown to be reduced considerably with the surfactant. The study shows that resistance to heat erosion equivalent to a silicone rubber filled with 30 weight % of micro-sized silica can be obtained with only 2.5 weight % of fumed nano silica and surfactant.nanofilled silicone rubber infrared laser heating, hot spot heating dry-band arcing wet composite insulators.

Analysis of temperature profiles and protective mechanism against dry-band arcing in silicone rubber nanocomposites

The paper discusses the mechanism by which nanofillers improve the erosion resistance of silicone rubber nanocomposites under simulated conditions of dry band arcing. Various micro-nano composites are studied, including microfiller, nanofiller, combinations of both, and with a commercial surfactant to improve the dispersion of the nanofiller. The thermal conductivity of the composites, measured using a standard method, shows higher thermal conductivity when the nanofiller is well dispersed. A thermal model is developed and solved with finite element method (FEM) to examine the temperature profile in the modelled nanocomposites under laser heating, which simulates the hot spot from dry band arcing. The hot spot is compared to the measured temperature profile by an infrared camera. SEM, EDAX, and XRD techniques are used to analyze the thermally decomposed silicone residue after laser heating to elucidate the protective mechanism in the silicone rubber nanocomposites.

Performance of hydrophobicity of different polymeric insulators in an accelerated ageing test

Hydrophobicity of polymeric insulators is one of the main properties that determine their performance in polluted environments. The hydrophobic property is reduced as the insulators surface ages due to the electric activity caused by wetting and pollution; however, it is recovered during the resting time in air. The insulators having a high rate of hydrophobicity recovery show better performance. Polymeric insulators of different materials and leakage distances were evaluated in laboratory by using an accelerated ageing method. The hydrophobic property of each insulator was studied by measuring the contact angle on the insulators surface where the highest electric activity was observed. The measurements were performed before and several times along the ageing test. The performance of the insulators was evaluated by the number and magnitude of the peaks of leakage-current recorded by a home-made system during the entire test. The results show than if the hydrophobic property of the insulators surface is low, the performance of the insulator under wet and polluted conditions may be strongly affected by its leakage distance.

Thermogravimetric and Spectroscopy Analyses of Silicone Nanocomposites

In this research, nanofillers, such as nano fumed silica, nano natural silica and nano alumina, are used to reinforce silicone rubber. The thermal degradation of the nanofilled samples are analyzed through thermal gravimetric analysis (TGA). TGA confirms that nano fumed silica imparts better heat resistance to silicone than nano natural silica or nano-alumina filler when dispersed with Tritontrade. Fourier transform infrared (FTIR) spectroscopy is used to elucidate the mechanism by which the nanofillers improve the heat and erosion resistance of silicone composites. FTIR analysis indicates a significantly higher concentration of silanol groups in the nano fumed silica filled samples than in the micro-silica filled samples. The influence of the increased number of silanol groups on the erosion resistance of the nanocomposites is discussed.

Silicone rubber and EPDM micro composites filled with silica and ATH

Since the 1970s two basic polymer compositions have been in use for outdoor electrical insulation applications as an alternative to porcelain and glass; these compositions are based on silicone rubber (SiR) and Ethylene Propylene Diene Monomer (EPDM) and a mixture of these two compositions, called an alloy, is also in use. To impart erosion and tracking resistance under dry band arcing to these compositions when used for outdoor electrical insulation, various fillers such as alumina trihydrate and various silicas, natural and synthetic, are used. This paper discusses the effect of the addition of inorganic microfillers into silicone and EPDM compositions. Two types of microfillers were used in this study; namely, ATH and micro silica. The inclined plane test, according to ASTM D2303, was used to evaluate the tracking and erosion resistance of the micro filled composites. For SiR composites, at the same filler loading, no clear distinction could be found between the two types of fillers in the prevention of erosion in the inclined plane test. However, it became quite clear that EPDM composites with ATH filler are less prone to erosion than EPDM composites with silica filler.