The condensation mechanism of the insulators’ surface, increase the surface electrical conductivity. The electrical conductivity of the insulator creates a high level of leakage current and causes the failure. Difference between the dew point and the surface temperature of the insulator which occur due to radiative cooling mechanism, is the major reason of the moisture condensation on the polluted insulator surface. To compensate for the temperature difference, carbon nanotubes (CNTs) are being added to the silicone rubber housing material. The main idea of this research is based on generating joule heating by reducing the surface resistance of high voltage insulators. For this purpose, a developed model based on Halpin–Tsai formulation for tensile modulus of nanocomposites is joined with the conventional power-law model for the effective electrical conductivity of silicone rubber matrix carbon nanotube composite (SMCNT). SMCNT samples are prepared with the addition of various CNT volume fractions to high temperature vulcanizing (HTV) silicone rubber by melt-blending method. The developed model reveals that the high fraction of thinner and longer CNT, thicker interphase, higher concentration of percolated CNT, lower waviness of CNT, and higher conductivity of CNT can make a higher effective conductivity for SMCNT.
Considerable cause of the condensation mechanism of moisture and fog on the contaminated high-voltage insulator surface is the temperature difference between the insulator surface and the dew point which eventuate owing to the mechanism of radiative cooling. Condensation of moisture leads to creating a conducting path on the insulator surface and make the insulator to be a conductor and results in the electrical transmission line failure. In order to cover the above-mentioned temperature difference, carbon nanotubes (CNTs) are being applied to the silicone rubber which is the insulator housing material. This study is based on joule heating generation which decrease the electrical resistance of the high-voltage insulator surface. An advanced mathematical model which is based on Pukanszky formulation for estimation of composite tensile strength was presented for the effectual electrical conduction of silicone rubber - carbon nanotube nanocomposite (SCNT). SCNT samples were produced by the addition of dissimilar CNT concentrations to a high temperature vulcanizing (HTV) silicone rubber by solution-blending method. Comparison between experimental results and theoretical forecasts showed an excellent agreement. The obtained model disclosed that the lower ranks of tunneling resistivity and distance, the higher magnitudes of tunneling diameter, the higher concentration of longer and thinner CNTs, lower CNT curliness, higher fraction of networked CNTs, and deeper interphase can produce the maximum level of SCNT conductivity.
Effects of fog condensation and fine dust on the high-voltage insulator surface are harmful. The insulator housing material (silicone rubber) must be changed in order to allow a controlled leakage current to flow on the surface and causes Joule heating effect. Accordingly, surface temperature of the insulator is increased and fog condensation on the insulator surface is prevented. For this purpose, silicone rubber - multiwalled carbon nanotubes (MWCNT) nanocomposites (SRCNT) were prepared using two different processes: a solution-blending (SB) method and a dry-state of melt-blending (MB) method. Field Emission Scanning Electron Microscopy (FESEM) images indicated that the MWCNT dispersion in silicone rubber matrix of SRCNT samples produced by SB method is much better than that of MB method. Fourier Transform Infrared (FTIR) spectroscopy determined the possibility of a greater reduction in hydrophobicity properties in the sample prepared by the SB method compared to the sample made by the MB method, and the contact angle measurements confirmed this expectation. Furthermore, in a same MWCNT concentration, the electrical conductivity of SRCNT samples prepared by SB method are greater than those produced by MB method. Results showed that MB is a high efficient method for producing the SRCNT in a large amount.
In this paper, a new model has been proposed to estimate the electrical conductivity of polymer carbon nanotube (CNT) nanocomposites based on the conventional power-law model and Halpin-Tsai formulation. Halpin-Tsai model was originally presented to calculate the tensile modulus of composites, which can be modified for the estimation of the electrical conductivity by replacing the electrical parameters. The nature of the "b" exponent in the power-law model is defined according to CNT dimensions, CNT electrical conductivity, and the interphase thickness, and also the impacts of these parameters on the "b" and the electrical conductivity of nanocomposite are taken into consideration. The developed model interprets that the electrical conductivity of polymer-CNT nanocomposite increases as the concentration, length, and electrical conductivity of CNT and the interphase thickness increase. Furthermore, reduction in CNT diameter and waviness results in the growth of nanocomposite electrical conductivity. In order to validate the developed model, nanocomposite samples with different volume fractions were produced by the solid-state technique of the melt-blending method. The results of calculations and experimental procedures show good agreement.
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