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In this paper, a new aging platform combined the high voltage electric field and the hydrothermal environment was built. To investigate the aging mechanism, physicochemical, dielectric and trap properties of HTV SR before and after electrical-hydrothermal aging for 24 days were discussed. The results indicated that, compared with hydrothermal aging...
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... In characterization filler material alumina contributed majorly toward the degradation. A new concept of electrical -hydrothermal aging mechanism was carried out on the SiR materials in [16]. The breakage of main chain of poly dimethyl siloxane (PDMS) along with production of free radicals with low molecular weight are the factors attributing to the decrease in dielectric and mechanical strength. ...
The organic nature of composite insulators makes them vulnerable under various stress even though they offer many advantages compared to ceramic counterparts. This premature aging will create a major change in surface profile, variation in chemical bonding and hydrophobicity. Those factors will make the polymers lose their insulation property, resulting in an increase in leakage current, causing frequent flashover. This can ultimately make insulators of this type fail at normal operating voltage, causing disruption in power utilities, resulting in huge economic losses. So in this regard an attempt has been made by the author in the work to understand the chemical phenomena behind this premature natural aging. The various categories of insulators with profiles termed as virgin, 2 years aged, 3 years aged with bio growth, shrinked and flashover has been collected from the marine environment. Analysis of the insulators by Fourier transform infrared spectroscopy indicates that as the insulators age there will be serious decrease in aging resistance, degradation resistance and hydrophobic property. Shore A hardness indicates the surface becomes very hard with aging causing decrease in surface resistance. Water contact angle measurements indicate that material tends to become more hydrophilic. The silica oxidation, oligomer formation and shielding effect reduction are the main factors leading to the insulation failures of field aged insulators. This work will help power system engineers timely replace aged insulators of the type and prevent huge economic losses to the utility industry.
... (3) As for the high temperature vulcanization of SR, it also needs to be heated to 150 • C and kept for 2 h in processing [50]. ...
Polymeric insulating materials is the basis of electric power system and has been widely employed in various electric power system apparatus. With the emergence of net-zero carbon emission policies by 2050-2060, the eco-friendly polymeric insulation is urgent and promising in the R&D of advanced dielectric materials. This paper reviews the current progress of eco-friendly upgrade in each lifecycle stages of polymeric insulating materials, i.e. raw material, fabricating, operating, and retiring. A series of interesting and fundamental results have been summarized. Drawbacks of the current researches are discussed, and outlooks are provided for the future development of eco-friendly polymeric insulating materials. This paper is hoped to inspire some novel ideas for the development of advanced insulating materials suitable for the promotion of net-zero carbon emission technologies.
... The synergistic effect of UV light, salt, fog, humidity, acid rain and heat on the performance of silicone rubber and its composites was reported by Khattak et al. [21]. The hydrophobicity recovery phenomenon of both RTV and HTV silicone rubber under different stresses was investigated in various studies, implying that the transfer of Low Molecular Weight (LMW) components from material bulk to the surface is the main reason for the recovery of hydrophobicity of silicone rubber [22][23][24][25]. Ahmadi-veshki et al. concluded that pollution and humidity increased the probability of occurrence of flashover [26]. ...
Silicone rubber is a promising insulating material that has been performing well for different insulating and dielectric applications. However, in outdoor applications, environmental stresses cause structural and surface degradations that diminish its insulating properties. This effect of degradation can be reduced with the addition of a suitable filler to the polymer chains. For the investigation of structural changes and hydrophobicity four different systems were fabricated, including neat silicone rubber, a micro composite (with 15% micro-silica filler), and nanocomposites (with 2.5% and 5% nanosilica filler) by subjecting them to various hydrothermal conditions. In general, remarkable results were obtained by the addition of fillers. However, nanocomposites showed the best resistance against the applied stresses. In comparison to neat silicone rubber, the stability of the structure and hydrophobic behavior was better for micro-silica, which was further enhanced in the case of nanocomposites. The inclusion of 5% nanosilica showed the best results before and after applying aging conditions.
High-temperature vulcanized silicone rubber (HTV-SR) employed for composite insulators is continuously subjected to a complex environment of alternating heat, corona discharge, humidity, etc. These stresses (especially alternating heat) complicate the aging mechanism of HTV-SR, which lacks systematic investigation. In this paper, a multi-factor aging platform considering temperature cycling, moisture, and corona discharge is established. Specifically, four temperature-cycling settings are employed, each of which lasts for 15 cycles. The surface morphology, hydrophobicity, and chemical, mechanical, and electrical properties of aged samples are methodically characterized. Experimental results show that the aging degree is correlated to the range of temperature cycling, which is attributed to diverse crosslink-degradation degrees with different temperature differences. Under a large temperature difference (70 °C), HTV-SR possesses a high crosslinking degree and a low degradation degree, making the material hard but easy to crack with alternating thermal stress. Then, severe defects and water condensation emerge on the HTV-SR surface, which promote the diffusion of corona products and water molecules into the material. The subsequent rise in crosslinking density caused by in-depth oxidation further exacerbates the aging of the material. Consequently, it brings about poor hydrophobicity, high interfacial polarization, and shallow trap energy levels in HTV-SR. This work provides a detailed analysis of the aging mechanism of HTV-SR in a simulated on-site environment.
Chalking of silicone rubber (SR) is a universal and important aging phenomenon. However, performing chalking simulation to study the aging performance of SR in the laboratory is difficult. In this study, a controllable artificial chalking method, which was based on selective scission reactions using methylcyclohexane (MCH) and diethylamine (DEA) as solvents, and tetramethylammonium hydroxide as the catalyst, was developed. Through controlling the ratio between DEA and MCH, different chalking degrees of SR could be realized artificially. The macroscopic observation, scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were conducted to compare the differences of samples with various chalking degrees. Furthermore, the control mechanism of the degree of chalking and the function of DEA during the artificial chalking process was elucidated. The results demonstrated that the artificial chalking method was feasible and could help identify the anti-aging ability of SR.
High temperature vulcanized (HTV) silicone rubber (SIR), as the sheath of composite insulators, is widely used as the insulation device in transmission lines due to their excellent hydrophobicity and pollution flashover resistance. However, the interfacial defects of insulators and severe operating environment will accelerate the aging of HTV SIR sheath, seriously affecting the operation reliability of electrical equipment. Herein, the samples designed with different sizes of interfacial defects are aged under water, sulfuric acid and nitric acid at 80 ℃, respectively. The results show that a large number of cracks appear on the surface of HTV SIR samples with interfacial defects after nitric acid treatment at 80 ℃ for more than 2 days, while samples with no interfacial defects aged under same condition for 8 days maintain unchanged. According to the results of the micro morphology of the sample, the crack is caused by the interfacial stress of the sample. In addition, after nitric acid treatment, the thermal stability, tensile and dielectric properties of HTV SIR with interfacial defects decreased significantly. The initial decomposition temperature decreases by about 30 ℃, while the residual weight increases by about 2.5 %. Meanwhile, the tensile strength and fracture strain decrease from 4.58 MPa and 470 % to 2.07 MPa and 130 % respectively, proving that cracks caused by interfacial defects can critically avianize the mechanical properties and thermal stability of HTV SIR. Also, there is an extra dielectric loss peak appearing in the frequency range of 10² Hz-10⁴ Hz, which attributed to water invading and the MWS polarization at cracks. By aging HTV SIR with artificial interfacial defects under thermal and acid stress, the HTV SIR cracking phenomenon of composite insulators under severe operating environment is successfully simulated. This work can provide theoretical support ulteriorly for studying the cracking mechanism and the corresponding aging characteristics of HTV SIR used in composite insulators.
The utilization of advanced propellants leads to unbearable temperature and pressure in propellent ramjet engines, paving the way for the enhancement of thermal insulation materials. High temperature vulcanized polydimethylsiloxane composites have been adopted due to the satisfactory ablation resistance at the expense of complicated industrial costs. For the purpose of simplifying the processes and enhancing the ablation resistance of polymer matrices, room temperature vulcanized hydroxyl-terminated polydimethylsiloxane (HPDMS) crosslinked with multi-ethoxy POSS (EOPS) coatings ([email protected] HPDMS) were prepared through capping crosslink. Comparative analyses of different EOPS loadings of [email protected] revealed the chemical bonding of EOPS ameliorated the effects about crosslinking properties, mechanical strengths, thermal performance and ablation resistance of HPDMS. This work could provide an optional method for developing advisable ablation resistance composites in aerospace applications.
