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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01 Sep 1971
TL;DR: In this paper, the influence of a number of parameters, such as surface conductivity, overall length, leakage-path length and profile on insulator flashover is discussed, and the effect of voltage waveshape is shown that direct voltage gives flashover at the lowest peak stress for a given pollution severity.
Abstract: High-voltage insulators may flashover at working voltage when polluted and wet. Pollution is deposited by various forces, of which aerodynamic ones are shown to be usually the most important. Theories to explain the pollution-flashover process are described. The performance of insulators in a polluted environment may be assessed by tests in natural conditions, or by the use of artificial methods, which are critically examined. The influence of a number of parameters, such as surface conductivity, overall length, leakage-path length and profile on insulator flashover is discussed. Studies of the effect of voltage waveshape show that direct voltage gives flashover at the lowest peak stress for a given pollution severity. Pollution flashover can be prevented by washing or greasing or by employing oil-bath or resistive-glazed insulators or special insulator assemblies. The advantages and disadvantages of these remedies are outlined. An analysis of the behaviour of polluted surge diverters and insulators with special functions introduces extra problems which are discussed. Organic insulating materials are degraded by tracking or erosion, but insulators using these materials have advantages, especially for ultra-high-voltage systems. An important aspect of the pollution problem which needs further study is the measurement of the site-pollution severity, so as to classify insulation requirements, and several methods of measurement are described.
87 citations
"Understanding the influence of wate..." refers background in this paper
...(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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TL;DR: In this article, surface charge decay on HTV silicone rubbers charged by impulse corona is studied, where surfaces of the materials exposed to corona were kept open to ambient air whereas the opposite surfaces were in contact with a grounded copper plate and surface potential distributions on the samples were measured using Kelvin type electrostatic probe.
Abstract: Surface charge decay on thick flat samples of HTV silicone rubbers charged by impulse corona is studied. In the experiments, surfaces of the materials exposed to corona were kept open to ambient air whereas the opposite surfaces were in contact with a grounded copper plate and surface potential distributions on the samples were measured using Kelvin type electrostatic probe. The developed procedure allowed for implementation of three study cases when (i) neutralization of pre-deposited charges by free ions present in air was prevented and surface potential decay occurred mainly due to bulk neutralization; (ii) gas neutralization took place under natural conditions and (iii) gas neutralization was enhanced due to increased amount of free ions in ambient air provided by nearby corona. Potential decay observed only due to bulk neutralization was used to evaluate voltage dependent conductivity of the materials and allowed for comparing them with those measured by the standard method. Comparison of decay characteristics observed for different test conditions were used to evaluate the relative importance of each mechanism on the total process of charge decay.
86 citations
TL;DR: In this article, a new laboratory test for evaluating the tracking and erosion performance of HV outdoor polymeric insulating materials is described, which is based on combining some features of the ASTM D2132 DF (dust and fog) test and the inclined plane test.
Abstract: A new laboratory test for evaluating the tracking and erosion performance of HV outdoor polymeric insulating materials is described. The materials evaluated include various formulations of HTV (high temperature vulcanized) silicone rubber and polyolefin polymers. The test is based on combining some features of the ASTM D2132 DF (dust and fog) test and the ASTM D2303 IP (inclined plane) test. The new test employs IP test geometry, IP test equipment, and IP specimen plaques. The plaque is coated with a mixture of clay and salt similar to the contaminant of the DF test and identical to the contaminant used in the IEC clean fog test to rate ceramic insulators for use in contaminated environments. A liquid contaminant with a conductivity similar to that of the DF test is applied to the test specimen in the same way as in the IP test. Data collected from the field on the maximum concentration of insoluble and soluble ionic materials on surfaces of contaminated insulators which have been for 21 years in contaminated regions, provide a basis for choosing the minimum concentration of the solid contaminant to apply to the specimens. This choice also serves to define, at least tentatively, the geographical area where the results of this test have significance. It is expected that this test could be used also for screening materials and obtaining a relative ranking of the tracking and erosion resistance of various materials. Measurements of the leakage current via a computerized data acquisition system, and the discharge activity with a high speed camera were performed, and have resulted in a better understanding of the onset of material degradation.
80 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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TL;DR: In this paper, the authors compared the performance of artificially corona-aged and naturally site-aged SIR materials and their properties such as hydrophobicity, leakage current, trap density/energy level, surface microstructure and chemical composition.
Abstract: During the field service of composite insulators, high temperature vulcanized (HTV) silicone rubber (SIR) material used for insulator’s sheath and sheds is gradually aging, and thus how to effectively evaluate its aging state has become an inevitable issue. In this paper, artificially corona-aged and naturally site-aged SIR materials are employed as samples, and their properties such as hydrophobicity, leakage current, trap density/energy level, surface microstructure and chemical composition are investigated for comparative study. With the increasing of corona aging intensity, the contact angle of SIR samples drops gradually and recovers more slowly. The hydrophobicity of site-aged insulators also declines, from HC1 for 2-year service to HC5 for 15-year service. The leakage current of corona-aged and site-aged samples both increase with aging, which indicates that aging induces the increase of surface conductivity of SIR material. The peak trap density of corona-aged and site-aged samples increases with the aging duration or service duration remarkably. The changes of these properties are attributed to the changes of micro-structures and compositions in the surface layer of SIR. The scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) analysis results reflect that a hardened inorganic silica-like (SiO2) layer with many polar chemical groups and distributed micro-pores is formed on the surface of SIR material after corona aging. Because of this silica-like layer, the hydrophobicity decreases while surface conductivity and trap density of SIR material increases. Besides the traditional properties like hydrophobicity and surface conductivity, the trap density is expected to be a novel parameter for effective evaluation of aging state of HTV silicone rubber material.
77 citations
TL;DR: In this article, surface charge decay on thick flat samples of high temperature vulcanized silicone rubber is studied prior and after ac and dc corona pre-treatments, and it is found that the charge decay rate on the material exposed to ac corona becomes much higher and sensitive to moisture content in the surrounding air.
Abstract: Surface charge decay on thick flat samples of high temperature vulcanized silicone rubber is studied prior and after ac and dc corona pre-treatments. It is found that the charge decay rate on the material exposed to ac corona becomes much higher and sensitive to moisture content in the surrounding air. These features are associated with an increased surface conductivity and formation of a silica-like layer on the polymeric surface, both resulting from ac corona treatment. In contrast, characteristics of the charge decay on the material exposed to dc corona are found to be similar to that measured on untreated samples.
65 citations