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.
Citations
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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 article, the authors presented a recurrent plot analysis of leakage current (LC) to evaluate the hydrophobicity of the silicone rubber insulator, which was carried out according to the dynamic drop test method.
Abstract: In order to reduce electrical accidents caused by aging of polymer insulators, hydrophobicity evaluation is one of the essential methods to monitor the practical performance of insulators. This paper presents recurrent plot (RP) analysis of leakage current (LC) to evaluate the hydrophobicity of the silicone rubber insulator. Experiments were carried out according to the dynamic drop test method. Dynamic behaviors of water droplets and the induced discharge phenomena were captured by using a high-speed camera fixed vertically to the specimen surface. LC was measured and extended to m-dimensional phase space by using a phase-space reconstructed method. The RP of LC was obtained to reflect the underlying mechanism of surface discharges in relation to the insulator hydrophobicity. The results indicate that the RP technique can give a visual method for the hydrophobicity evaluation. The increasing tendency in RP indicators can reveal the decrease of hydrophobicity.
29 citations
TL;DR: In this article, the characterization of surface discharges, including the discharge magnitude, pulse number, adjacent discharge magnitude and adjacent time interval, have been analyzed to evaluate the surface hydrophobicity of silicone rubber insulator.
Abstract: A Dynamic drop test (DDT) has been employed for hydrophobicity evaluation, which has proven the occurrence of different discharge phenomena in relation to the hydrophobicity variation. In this paper, based on DDT method, the characterization of surface discharges, including the discharge magnitude, pulse number, adjacent discharge magnitude and adjacent time interval, have been analyzed to evaluate the surface hydrophobicity of silicone rubber insulator. It is found that with the decrease of hydrophobicity, these characteristics apparently show an increasing tendency. The characteristic pattern of discharge pulse and discharge magnitude presents a twin-peak shape, in which both the increase of the discharge magnitude and the discharge pulse number of higher magnitude reflect the decrease of surface hydrophobicity. The characteristic pattern of adjacent discharge magnitude and discharge magnitude emerges to be an 'X' shape composed by the discharge spots, in which the larger value in both the spot density and the shape expansion reveals the decreasing hydrophobicity. The characteristic pattern of next time interval and discharge magnitude demonstrates the frequency of surface discharges increases with the decrease of surface hydrophobicity. Furthermore, the comparability between the discharge characteristic methods and the contact angle method is analyzed to obtain the higher similarity coefficients. Obtained results indicate that the characteristic of surface discharge in DDT method can be utilized to the hydrophobicity evaluation.
21 citations
Additional excerpts
...(1) alkyne C-H bend, (2) methylene (CH2) rocking, (3) methyne (CH) skeletal C-C vibrations, (4) organic siloxane (Si-O-Si), (5) methyne (CH) skeletal C-C vibrations, (6,7) phenol/tert-alcohol bend, (8) quinone/conjugated ketone, (9) methyl C-H stretch, (10) methyl C-H asym....
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19 Oct 1997
TL;DR: In this article, a laboratory test to evaluate and compare the tracking and erosion resistance of high voltage (HV) outdoor polymeric insulating materials is described, based on combining some features of the ASTM D-2132 Dust and Fog test, and ASTMD-2303 Inclined Plane test.
Abstract: A laboratory test to evaluate and compare the tracking and erosion resistance of High Voltage (HV) outdoor polymeric insulating materials is described. The test is based on combining some features of the ASTM D-2132 Dust and Fog test, and ASTM D-2303 Inclined Plane test. The experimental conditions employed can be related to actual field conditions, hence the results obtained provide a more realistic evaluation of materials' tracking and erosion performance. Measurements of leakage current via a computerised data acquisition system, and discharge activity with a high speed camera were performed to develop a better understanding of the onset of material degradation. The materials evaluated include various formulations of High Temperature Vulcanising (HTV) silicone rubber and polyolefin polymers.
15 citations
TL;DR: In this paper, it was found that an increase in droplet volume and number of droplets within the gap reduces the CIV and the magnitude of discharge current flow is high under negative polarity.
Abstract: Epoxy nanocomposites with different percentages of nano clay filler are prepared using a shear mixer technique. Corona inception voltage (CIV) due to water droplets on the epoxy nanocomposite is high under negative direct voltage compared with positive polarity voltage. It was found that an increase in droplet volume and number of droplets within the gap reduces the CIV. The magnitude of discharge current flow is high under negative polarity. Surface charge accumulation studies indicate nonlinear variation in distribution of charges on the surface of the epoxy nanocomposite with water droplets. Optical Emission Spectroscopy (OES) results confirm high temperature plasma during water droplet initiated electrical discharges on the surface of epoxy resin. Laser Induced Breakdown Spectroscopy (LIBS) results indicate the presence of carbon on the degraded surface of the sample. The absorbed energy on the sample surface during arcing is measured through leakage current, and is observed to be higher for negative polarity. UHF signals were radiated due to corona discharges from water droplets on the epoxy nanocomposites under direct voltages and their bandwidth is in the range of 1–2 GHz.
12 citations
26 Feb 2014
6 citations