Understanding the influence of water droplet initiated discharges on damage caused to corona-aged silicone rubber
13 Sep 2017-IEEE Transactions on Dielectrics and Electrical Insulation (IEEE)-Vol. 24, Iss: 4, pp 2421-2431
TL;DR: In this paper, surface charge accumulation studies indicate that the charge retention capability of the insulating material gets reduced drastically with silicone rubber damaged due to corona, causing degradation of surface.
Abstract: Corona activity on the surface of silicone rubber has high impact on variation in hydrophobicity of the material, and on corona inception voltage (CIV) of water droplet sitting on the corona degraded surface. The CIV is high under negative DC as compared to positive DC/AC voltages. Increase in conductivity of water droplet reduces CIV. Surface charge accumulation studies indicate that the charge retention capability of the insulating material gets reduced drastically with silicone rubber damaged due to corona causing degradation of surface. Irrespective of the number of cycles of corona discharge activities carried out, the time constant of charge decay, after the removal of charge injection, remains the same. The water droplet initiated discharges under AC and DC voltages radiate UHF signal in the bandwidth 0.3–1.2 GHz. With single droplet sitting on top of the corona damaged silicone rubber, the amount of charge retained by the water droplet is low when the droplet is placed and charged immediately after corona discharge activity to surface of the insulating material. When the water droplet is placed after a certain time period, the charge accumulation characteristics of silicone rubber are regained. Leakage current measured during water droplet discharge studies through recurrent plot (RP) analysis reveals that, under AC voltage, it is possible to classify corona inception, arcing and bridging of water droplet between high voltage and ground electrode. The RP obtained for the current signals generated due to water droplet discharges under positive and negative DC voltages are different. The amount of damage caused to silicone rubber due to water droplet is high under negative DC voltage as compared to positive/AC voltages. While correlating the level of damage to the insulating material due to water droplet and the RQA parameters of RP, it is observed that higher the recurrence rate along with high determinism can cause severe damage to the insulating material. Structural analysis using ATR-FTIR and pyrolysis-GC/MS studies reveal significant functional group variation on surface of silicone rubber, especially when the number of cycles of corona ageing is more.
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TL;DR: In this article , the authors focused on the effect of fillers on the improvement of the thermal conductivity, dielectric strength, mechanical strength, corona discharge resistance, and tracking and erosion resistance performance of polymeric materials for use as highvoltage transmission line insulators.
Abstract: In the present literature survey, we focused on the performance of polymeric materials encompassing silicone rubber (SiR), ethylene propylene diene monomer (EPDM) and epoxy resins loaded with micro, nano, and micro/nano hybrid fillers. These insulators are termed as composite insulators. The scope of the added fillers/additives was limited to the synthetic inorganic family. Special attention was directed to understanding the effect of fillers on the improvement of the thermal conductivity, dielectric strength, mechanical strength, corona discharge resistance, and tracking and erosion resistance performance of polymeric materials for use as high-voltage transmission line insulators. The survey showed that synthetic inorganic fillers, which include silica (SiO2) and hexagonal boron nitride (h-BN), are potential fillers to improve insulation performance of high-voltage insulators. Furthermore, nano and micro/nano filled composites performed better due to the better interaction between the filler and polymer matrix as compared to their only micro- or nano filled counterparts. Finally, some aspects requiring future work to further exploit fillers are identified and discussed.
30 citations
01 Mar 2019
TL;DR: In this paper, numerical simulation and experimental investigation on dynamic formation mechanism of water droplet and induced surface discharges on silicone rubber composites under different AC voltages, considering the factors of surface tension and droplet volume.
Abstract: Wettability has become one of the most important factors influencing power equipment insulation system in coastal power grid, which can seriously threaten the safety of power grid. This paper aimed at numerical simulation and experimental investigation on dynamic formation mechanism of water droplet and induced surface discharges on silicone rubber composites under different AC voltages, considering the factors of surface tension and droplet volume. Obtained results reveal that the spreading coefficient increases with increasing the electric field intensity from 1 to 5 kV/cm and with increasing the droplet volume from 10 to 50 µL. The spreading coefficient shows a decreasing tendency when the surface tension increases from 29.3 to 61.0 mN/m. Moreover, the maximum of surface electric field shows an increasing tendency under the condition of increasing both the droplet volume and the surface tension. On the basis of the physical model of droplet deformation, the electric field force and the surface tension play a significant role in the process of droplet deformation. Meanwhile, the experimental results are consistent with the simulation analysis, reflecting that the droplet deformation and the induced surface discharges mainly depend on two parameters: the droplet volume and the magnitude of applied voltage.
13 citations
TL;DR: In this paper, the effect of corona discharges on the surface morphology characteristics of the nanocomposites was analyzed by measuring contact angle, surface profile measurement using atomic force microscopy (AFM), and characterized by multiresolution signal decomposition (MRSD) technique.
Abstract: Silicone rubber nanocomposites were prepared using 1, 3, 5, and 10 wt% of alumina nanofiller. Corona inception voltage (CIV) due to water droplets was measured using fluorescence technique, and it has decreased for alumina-added silicone rubber nanocomposites and with corona-aged samples. The effect of the corona discharges on the surface morphology characteristics of the nanocomposites was analyzed by measuring contact angle, surface profile measurement using atomic force microscopy (AFM), and characterized by adopting multiresolution signal decomposition (MRSD) technique. The addition of the alumina nanofiller suppressed the surface roughness for the corona-aged nanocomposites and 5-wt% sample observed to have the lowest surface roughness values. Recovery of the surface roughness caused by corona discharges was analyzed at different time intervals, and it was observed that alumina nanoparticle-added silicone rubber showed an incremental reduction in the roughness recovery rate. The laser-induced breakdown spectroscopy (LIBS) technique was adopted to analyze the nanocomposites after the corona aging, and further plasma temperature was evaluated at different recovery times. The addition of an alumina nanofiller increased the plasma temperature, and 5-wt% samples have the lowest plasma temperature recovery rate after corona aging. The analysis of the study indicates that the corona-aged silicone rubber specimen surface properties recover in 8 h of resting time period.
12 citations
TL;DR: In this article, the performance of base epoxy resin (S1) is compared with epoxy resins with ion trapping particle (Sample S2) and epoxy reagents with nanotitania particle (S3) particle.
Abstract: Epoxy nanocomposites being used in the high-energy radiation zones as an insulant may undergo changes in their dielectric properties during service. In the present study, the performance of base epoxy resin (S1) is compared with epoxy resin with ion trapping particle (Sample S2) and epoxy resin with nanotitania (Sample S3) particle. The influence of gamma irradiation on nanocomposites was analysed. Corona inception voltage due to water droplet initiated discharge and contact angle reduces post-gamma-ray irradiation. Surface potential decay time constant reduced drastically for gamma-ray-irradiated specimens. Trap distribution characterisation indicated that charge mobility increases after irradiation. The surface roughness of the sample increases with the irradiation dosage. Dielectric relaxation spectroscopy shows that permittivity reduces and loss tangent increases with the gamma-irradiated specimens. Water diffusion rate increases for the gamma-ray-irradiated specimen. No change in elemental composition, measured using laser-induced breakdown spectroscopy, of test specimens was observed. The hardness of the material and plasma temperature formed during laser shine decreases with gamma-ray irradiation intensity for Sample S1, whereas samples S2 and S3 showed only marginal variation. The performance of Sample S2 is found to be better than Samples S1 and S3.
12 citations
16 Oct 2019
10 citations
References
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TL;DR: In this paper, epoxy nano composite samples of different clay content are subjected to water droplet initiated discharge tests using controlled harmonic content high voltage supply, and the effect of a clay additive up to 1% by weight is shown to increase droplet contact angle by 8% with a subsequent reduction beyond this content.
Abstract: In the present work, epoxy nano composite samples of different clay content are subjected to water droplet initiated discharge tests using controlled harmonic content high voltage supply. The effect of a clay additive up to 1% by weight is shown to increase droplet contact angle by 8% with a subsequent reduction beyond this content. Using a UHF technique to identify the corona inception voltage, it is difficult to identify correlation with harmonic content. However, it was found that the corona inception factor (CIF) and the peak factor of the applied AC/harmonic AC voltages showed an inverse relationship. The rise time of the current pulse due to water droplet initiated corona discharge under AC/harmonic AC voltage was found to be about 700 ps and from FFT analysis, the corresponding UHF generated signal has a dominant frequency of about 1 GHz. The characteristics of the captured UHF signals are similar for all investigated clay contents and harmonic AC voltages. It was found that the discharges caused damage near the high voltage electrode and that the surface carbonization is related to the accumulated dissipated energy during the discharge process. Analysis of the voltage, current signals and phase resolved partial discharge (PRPD) studies indicate that discharges occur around the voltage peak and also when the rate of rise of voltage is high. The number of discharges is higher in the positive half cycle compared with the negative half cycle.
6 citations
31 Oct 2008
TL;DR: In this paper, an attempt has been made to understand the characteristics of corona/arcing discharges from water droplet under high electric field, in epoxy nanocomposites, adopting Ultra high frequency (UHF) measurement technique and by Acoustic Emission (AE) technique.
Abstract: In the present study an attempt has been made to understand the characteristics of corona/arcing discharges from water droplet under high electric field, in epoxy nanocomposites, adopting Ultra high frequency (UHF) measurement technique and by Acoustic Emission (AE) technique. The exfoliated/intercalated properties of the nanocomposites were analyzed through transmission electron microscopy (TEM) studies. The hydrophobicity of the material characterized through contact angle measurement.
3 citations