Search

In this study, we have investigated the relationship between the plasma temperature in remote laser-induced breakdown spectroscopy (LIBS) experiments and the hydrophobic properties of silicone rubber insulators (SIRs). Contact angle and LIBS measurements were conducted on both artificially-aged (accelerated aging) and field-aged SIRs. This study reveals a clear connection between plasma temperature and the properties of aged SIRs on artificially-aged SIR specimens. Specifically, the plasma temperature exhibits a consistent increase with the duration of the accelerated aging test. The hydrophobicity of the artificially-aged SIRs was assessed by performing contact angle measurements, revealing a decrease in the hydrophobicity with increased aging test duration. Furthermore, we extended our investigation to the study of nine field-aged SIRs that had been in use on 150 kV overhead transmission lines for 0 to 21 years. We find that the laser absorption and hardness of the material do not relate to the plasma temperature. In summary, we observe a direct connection of plasma temperature to both contact-angle measurements and operation time of the in-service insulators. These results strongly suggest the potential use of LIBS for remotely evaluating the hydrophobicity and aging degree of silicone rubber insulators, thus assessing their real-time on-site operational quality. [ABSTRACT FROM AUTHOR]

In this study, we have investigated the relationship between the plasma temperature in remote laser-induced breakdown spectroscopy (LIBS) experiments and the hydrophobic properties of silicone rubber insulators (SIRs). Contact angle and LIBS measurements were conducted on both artificially-aged (accelerated aging) and field-aged SIRs. This study reveals a clear connection between plasma temperature and the properties of aged SIRs on artificially-aged SIR specimens. Specifically, the plasma temperature exhibits a consistent increase with the duration of the accelerated aging test. The hydrophobicity of the artificially-aged SIRs was assessed by performing contact angle measurements, revealing a decrease in the hydrophobicity with increased aging test duration. Furthermore, we extended our investigation to the study of nine field-aged SIRs that had been in use on 150 kV overhead transmission lines for 0 to 21 years. We find that the laser absorption and hardness of the material do not relate to the plasma temperature. In summary, we observe a direct connection of plasma temperature to both contact-angle measurements and operation time of the in-service insulators. These results strongly suggest the potential use of LIBS for remotely evaluating the hydrophobicity and aging degree of silicone rubber insulators, thus assessing their real-time on-site operational quality.

Insulator leakage current is the primary root cause of pole fires; therefore, it is critical to recognize outdoor insulators as potential cause of wildfires. [ABSTRACT FROM AUTHOR]

Insulators' flashover due to pollution is the biggest challenge of power systems. This phenomenon will become more intense with the aging of the insulator. Precise and prompt determination of the severity of pollution and the insulator status in terms of aging is essential for preventing pollution flashovers. Therefor monitoring insulator leakage current is essential for preventing the pollution flashover phenomenon. This article proposes innovative criteria based on the insulator's leakage current analysis for the classification of aging and pollution severity. The leakage current signal of the virgin, fully aged, and asymmetric aged insulators have been examined under different pollution conditions. Based on the experimental results analysis, two new criteria have been proposed for assessing the silicon rubber insulator condition which have resulted from the first-order harmonic of leakage current (I t 1 ), the third and fifth-order harmonics ratio of leakage current (I t 3 / 5 ), and the cosine of first-order harmonic phase angle (P I). Analyzing the proposed criteria demonstrates that two proposed criteria have a strong correlation to aging and pollution, respectively. These two new criteria can be implemented to identify the early signs of pollution and aging of insulators. The ability of proposed criteria has been established based on random forest, support vector machine, decision tree algorithm, multi-layer perceptron, and decision-making level fusion in Python language. The obtained criteria based on experimental data in different conditions have been employed for classifier training which can be applied in industrial settings without the need for laborious data labeling, ensuring fast and accurate outcomes. [ABSTRACT FROM AUTHOR]

Using an experimental approach, the effectiveness of nonionic surfactant, Triton™-X-100 in dispersing nano Alumina in high temperature vulcanized silicone rubber are studied in detail. Nanocomposites are prepared in varying concentrations of 0, 0.01, 0.05, 0.2, 1, and 5 phr levels by weight of the surfactant. Evidence to moderate dispersion of nano Alumina for composites at 0.01 phr and 0.05 phr weight loadings is gained from SEM pictures. Structural changes observed for the composites in FTIR spectra are examined and peaks identified. Thermogravimetric analysis shows some improvement in thermal resistance. However, an adverse effect on properties, such as volume resistivity, surface resistivity and dissipation factor are observed even at low surfactant loadings. A plausible role of surfactant as a plasticizer is explained with respect to the results of tensile strength. From this work, it can be inferred that surfactant at 0.01 phr may be taken as an optimum loading concentration for a desirable level of electrical properties, without compromising on insulation characteristics of volume resistivity and dissipation factor. Nonetheless, utmost caution needs to be exercised while employing Triton™-X-100 in compositions prepared for insulation applications because of inadequacies in values of volume resistivity, surface resistivity, dissipation factor and dry arc resistance even at low loadings. [ABSTRACT FROM AUTHOR]

Surface tracking and erosion is an irreversible degradation occurring on the insulator surface, and this can ultimately lead to failure of the insulator. Polymeric materials such as silicone rubber have many advantages; including a superior hydrophobic surface. However, polymers are exposed to ageing and degradation resulting from electrical and environmental stresses. The rotating wheel dip test is adopted to conduct a comparative study of surface conduction on the two insulators. A conventional design has been selected and compared with insulators having textured surface. Monitoring of the shed surface and insulator trunk using an IR camera were carried out to assess the temperature distribution along insulator profiles. A spatial analysis was also performed to identify key features of the two designs. Localised surface conductance measurements are proposed in this study. This helps to understand and distinguish the trends of conductance and its distribution on each surface, helping to predict the future surface degradation associated to each design.

This study aims to predict the flashover voltage (FOV) of silicone rubber (SiR) insulators. Accordingly, it benefits from two methods, including an artificial neural network (ANN) model and a FOV gradient fitting model. The FOV and leakage current (LC) tests are carried out on one un‐aged and three aged specimens under uniform and longitudinal non‐uniform pollution circumstances. The proposed ANN model is designed based on equivalent salt deposit density (ESDD), pollution non‐uniformity degree, aging time, LC first harmonic magnitude I1, and total harmonic distortion. Furthermore, a FOV gradient model is proposed based on ESDD, I1, and creepage distance. To validate the proposed models, the FOV and LC tests are conducted on two different types of SiR insulators. Then, the predicted FOV from the ANN model and calculated FOV from the voltage gradient model are obtained. The results indicate that the relative errors of the ANN model and FOV gradient fitting model are <6.4 and 7.3%, respectively. [ABSTRACT FROM AUTHOR]

Atmospheric snow accretion along the insulators can eventually bridge adjacent shed spacing, which pose severe risks to the security of power networks. Aiming to investigate the influence of snow accumulation on the electrical performance of various types of insulators, the flashover tests of snow‐accreted insulators were conducted. The effects of various factors on the electrical characteristics of insulators were analysed based on the experimental data. Results show that AC arc flashover gradient of the insulator covered with nonuniform snow accumulation is lower than that of the uniform snow‐covered insulator. The former is as low as 22.5% lower than the latter. Moreover, the AC arc flashover gradient of the porcelain and glass insulators is 0.27–6.27% higher than that of the DC. For a silicone rubber insulator, this gap is greater than 20%. The flashover gradient of the glass insulator is the minimum at the snow thickness of 10 mm. The flashover process of snow‐covered insulator is neither similar to that of the contaminated insulator nor different from that of the iced insulator but a combination of the two. The presented work helps to better understand the flashover mechanism of snow‐covered insulators, and take efforts to mitigate its effects. [ABSTRACT FROM AUTHOR]

Room temperature vulcanised (RTV) silicone rubber is widely used in electrical power system, applied to the glass or porcelain insulator surface to enhance insulation. RTV coatings get contaminated after long-term operation and need to be recoated. Contaminants accumulate and embed into the surface of base RTV coating, forming a hard-to-remove inorganic transition layer. Such sandwiched contaminant layer destroys the adhesion between original and reapplied silicone rubber coating greatly. Authors’ study innovatively reports a method to enhance interfacial bond properties of the RTV recoating with sandwiched contaminant layer, by using an atmospheric-pulsed discharge plasma jet (APPJ) for surface treatment. Water boiling test and 180-degree peel test were conducted to evaluate interfacial bond properties macroscopically. Scanning electron microscopy (SEM) was applied to observe the cross-section of recoating interface, while Fourier-transform infrared spectroscopy (FTIR) to detect chemical changes of contaminant layer, giving out microscopic and theoretical explanation.

Algae colonisation has been observed on silicone rubber insulators around the world especially in a subtropical climate because the moderate temperature and moisture could aggravate the growth of algae upon silicone rubber material. The surface of these insulators easily forms a water film, and the originally excellent hydrophobicity is decreased or even destroyed. This study explores the regularity of the hydrophobicity changes and the underlying mechanism. Based on the solid layer method, silicone rubber samples were found with algae and inorganics quantitatively, and their contact angles were measured after reservation under different humidity levels. The results showed that although inorganic ash could accelerate the hydrophobic recovery process, algae colonisation decisively decreased the hydrophobicity, especially in moist climates. After an extensive investigation of biological contaminants, it was found that the appearance of algae was independent of inorganics, but algae could accelerate the accumulation of inorganics through water absorptivity and the viscosity of secretions. The water absorption ability of algae was compared with that of inorganic ash and sugar, and their difference was deduced to be due to the environmental adaptability of the algae organisms, which was reflected mainly in a dry climate. The microscopy analysis of bio-contaminants was conducted through SEM.

The pollution on insulators is composed of various chemical components, which threaten the stability of external insulation. However, the existing insulation designs have not taken this issue into consideration. This work aimed to study the influence of pollution chemical components on flashover performance of insulators with various materials. Flashover tests of porcelain, glass and silicone rubber insulators polluted by eight types of common contaminants were conducted. Based on the test data, the influence of chemical components and their solubility on equivalent salt deposit density (ESDD) and insulator flashover performance were analysed; and the electrical properties of different types of insulators were compared. Results show that the ESDD contribution rate changes with chemical components. The dissolution characteristic has a significant influence on the measurement of ESDD; slightly soluble contaminants need to be considered separately. The corresponding insulator flashover gradient for ions can be summarised as Cl^−

High-temperature vulcanised (HTV) silicone rubber composite insulator has been widely used in extra-high and ultra-high transmission lines due to its excellent electrical and mechanical performance. In practice use, liquids may encounter the composite insulator intermittently and can lead to the degradation and deterioration of silicone rubber. In the present research, the effects of liquids immersion and subsequent drying on the surface properties of HTV silicone rubber were investigated by means of the contact angle measurement and surface physical morphology measurement which was further analysed in terms of the discrete wavelet transform method, multiresolution signal decomposition algorithm, and three-dimensional fractal dimension calculation. Based on the experimental results, the mechanism of the loss and recovery of the hydrophobicity of HTV silicone rubber surface during the liquids immersion and subsequent drying processes were further explained by taking into consideration the embedded water molecules (and/or hydrated ions) on the HTV silicone rubber surface and the synergy of the increase in roughness/fractal dimension and low molecular weight siloxanes diffusion. This study is helpful for better understanding of the change of surface properties of HTV silicone rubber caused by environmental and electrical stresses.

Since the insulators of transmission lines are exposed to different environmental conditions, it is important task to study insulators performance under different conditions. In this paper, silicone rubber insulators performance under different environmental conditions including rainy, icy, salt and cement are proposed and exactly is studied. Electric fields (E-fields) and voltage distributions along the insulator under various conditions have been evaluated. Moreover, the corona rings effects on insulator performance under these conditions have been presented. A 230 kV silicone rubber insulator is selected, modeled and simulated with finite element method (FEM) using the COMSOL software. The simulation is repeated for different environmental conditions and efficiency of corona ring for each scenario is evaluated. The results indicate that environmental conditions have a significant effect on the insulator performance and the corona ring somewhat alleviate the adverse effect of environmental conditions on the insulator performance. [ABSTRACT FROM AUTHOR]

This study presents two different methods under uniform and non‐uniform pollution layer in order to measure and calculate the leakage current (LC) of silicone rubber insulators. Experimental test for evaluating the LC analysis of polluted insulator have been done in a laboratory clean fog chamber. The electric field and potential distributions were obtained from finite element method software for 3D models. The mathematical background and circuit theory are described in details by a section of insulator and using the extended form factor formula. The surface conductivity used in the calculations was extracted from the measured LC after wetting rate. LC characteristics under 1 : 1, 1 : 2, 1 : 5 and 1 : 10 ratios of top to bottom surface salt deposit density on polymeric insulators are studied. To verify the proposed models of this study, the results of experimental data and two other approaches are compared with together before dry‐band formation. Moreover, a dynamic LC model under uniform pollution layer has been introduced and extended in order to calculate the LC when the formation of dry‐bands along the insulator surface occurs. The dynamic model is drawn from experimental data and measured surface conductivity. [ABSTRACT FROM AUTHOR]

Electric field analysis around high‐voltage insulators is with an extreme importance during the development of new polymeric insulators design. In this study, the authors combine the finite‐element method (FEM) with the design of experiment method to investigate and describe the behaviour of textured silicone rubber insulators. First, a 3D FEM model of different silicone textured surfaces is developed. The maximum electric field is calculated taking into account various available patterns of hemispherical protuberance having different diameters. Then the design of experiment methodology is adopted to reduce the number of simulations and to give more significance to the results. Various influencing factors were considered in this stage. Finally, the analysis of variance is used to evaluate the contribution of the studied factors and their interaction on the total variation of the studied responses. [ABSTRACT FROM AUTHOR]

Abstract Ice and contaminants accumulate on the surface of insulators, causing severe damage to the power system. To reduce the accumulation of ice and contaminants, a superhydrophobic coating based on silica nanoparticles and room-temperature vulcanized silicone rubber was prepared via the simple spray coating method. The icing processes of the hydrophilic, hydrophobic and superhydrophobic surfaces from −4 to −16 °C were detailedly recorded. At −8 °C and −4 °C, the water droplets rapidly rolled away from the cold superhydrophobic surface. At −12 °C, a delay in the ice accretion and a decrease in the ice volume on the superhydrophobic surface were achieved. At −16 °C, the anti-icing effect was not observed. The experimental results also showed that the superhydrophobic coating has a strong ability to restrain frost growth. Hence, the superhydrophobic coating can be applied on insulators to prevent icing flashover. Highlights • The superhydrophobic coating was prepared by a simple spray-coating method. • The surface exhibited a water contact angle of 165° and a sliding angle of 5.3°. • Water droplets rolled away from the superhydrophobic surface rapidly at −4 and −8 °C. • Water droplets freezing could be delayed and reduced on the surface at −12 °C. [ABSTRACT FROM AUTHOR]

Silicone rubber is widely used in power system insulation for its hydrophobicity and hydrophobicity transfer to prevent pollution flashover. The influence of low molecular weight (LMW) siloxanes on hydrophobicity of contaminated silicone rubber after plasma jet treatment was investigated in this study. Experimental results show that plasma jet treatment for several seconds can significantly improve the hydrophobicity of contaminated silicone rubber. LMW siloxanes play an important role in the quick recovery of hydrophobicity induced by plasma jet treatment. Extraction of the LWM siloxanes from the silicone rubber decreases the contact angle after plasma treatment. Fourier transform infrared (FTIR) spectroscopy shows that hydrophobic groups appear on the surface of the contamination layer. The hydrophobicity improvement of contaminated silicone rubber results from LMW siloxanes transferred to the contamination layer during plasma treatment and the LMW siloxanes are mostly original uncrosslinked siloxanes in the silicone rubber. The molar mass distributions of the LMW siloxanes in hydrophobic contamination of treated specimens were similar with naturally transferred ones. X-ray photoelectron spectroscopy shows that an inorganic layer appears after plasma aging, which obscures the transfer of LMW siloxanes and reduce the hydrophobicity during plasma treatment. [ABSTRACT FROM AUTHOR]

To study effects of pressure, humidity and aging time on the corona aging process, aging characteristics of silicone rubber composite insulators were researched by orthogonal tests. The test platform of adjustable pressure and humidity was constructed. TSC, SEM and FTIR tests were selected for aged samples. By the range analysis, it showed that the effect of pressure on trapped charges was related to humidity and aging time. There were more trapped charges when the humidity was higher, and the influence of humidity was more obvious along with the longer aging time at a low pressure. As the pressure increased, however, the effect of humidity on trapped charges was gradually reduced. But the influence of aging time was more significant, while aged degree of silicone rubber was deepened with increasing aging time. Furthermore, the aging state of materials was the collaboration effect of charged particles and nitric acid. Moreover, it could be seen from TSC, SEM and FTIR tests, sorting results of aging states were inconsistent. Results showed that the TSC test was comprehensively embodied the corona aging characteristics caused by physical and chemical defects. Therefore, results of TSC tests could be selected as an effective criterion for aging evaluations. [ABSTRACT FROM AUTHOR]

Due to their weak weather ability, the ageing process of organic silicone rubber composites remarkably influences the service performance of composite insulators and bushings, especially in high-voltage transmission lines. In this study, laser-induced breakdown spectroscopy (LIBS) was used for analysing ageing composite insulator sheds for potential on-site application. A spectrum was recorded after each laser pulse and the element composition of ablated materials with different depth was observed. A calibration curve that revealed linear relationship between C, Si, Al spectrum line intensity and corresponding element concentration was established with the result of X-ray photoelectron spectroscopy test. Regularly line intensities of C, Si and Al changed dramatically from the surface to the bulk layer. Given the number of laser pulses with varying element concentrations, as well as the linear relationship described above, the depth of ageing layer could be calculated immediately. Also, the result was verified by secondary ion mass spectrometry and scanning electron microscope. LIBS method can be a promising and efficient technique to assess the ageing state of composite materials on site.

Abstract Silicone rubber based polymeric insulators are being used widely used as outdoor insulation for high voltage applications. However, their long-term service life performance is highly dependent on local environmental conditions that cause deterioration of material properties of the insulators. In the present work, tracking and erosion studies are conducted on silicone rubber samples using. Inclined Plane Tracking (IPT) and Erosion method based on IEC 60587. The contaminants used to simulate different environmental conditions are as per standard and in addition acidic rain composition is used. Leakage current flowing through samples was continuously monitored and recorded over the experimental duration. The consequence of leakage current variation is analyzed using. Recurrent Plot (RP) Analysis and this resulted in variation of quantitative parameters Recurrence Rate (RR), Determinism (DET), Entropy (ENT) and Length (L) these are used to interpret the tracking and erosion performance of silicone rubber samples. Further, physico-chemical analysis is conducted using Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDAX) and Fourier Transform Infra-Red (FTIR) spectroscopy to observe surface morphology and chemical changes happened in the samples. Thermo-Gravimetric Analysis (TGA) is performed to observe thermal stability and presence of Aluminum Tri-hydrate (ATH) fillers before and after experiments. The investigations show RP method as a potential tool for detection and diagnostic of polymeric insulators. Highlights • Investigations on tracking and erosion on polymeric insulators under AC stress is attempted • Leakage current monitored regularly for entire experimental duration • Significance of leakage current is analyzed using Recurrence plot analysis • Surface morphological changes on polymer insulators conducted • Investigations reveal material degradation, depolymerization and loss of ATH. [ABSTRACT FROM AUTHOR]

In this study, the results of measurement for DC flashover characteristics of silicon rubber insulators in the presence of surface charges and in terms of geometric characteristics have been examined and analysed. In the carried out experimental tests, the surface of different insulators was charged by an external corona source and both the metal end fittings were kept grounded while the needles have been connected to a certain applied negative and positive DC voltages and then surface electric charge measured. A series of flashover tests have been carried out on the charged insulators under positive DC voltages to investigate the effects of surface charges. The experimental results revealed that positive electric charges reduced flashover performance while negative charges increased the flashover voltage level. Also, the experimental modelling of DC flashover of charged insulators regarding the ratio of shed spacing to shed depth and specific leakage distance in terms of surface electric charges, revealed that flashover voltage gradient of the charged insulator is most affected by specific leakage. [ABSTRACT FROM AUTHOR]

In the present work, surface degradation studies are performed on silicone rubber based polymeric insulators using rotating wheel and dip test under DC voltage application. This work gains importance as number of HVDC lines are being constructed for transferring bulk power over long distances particularly in the country. A newly developed rotating wheel and dip test arrangement is used for the study; provision is made in the experimental set up to apply two different contaminants simulating different environmental conditions simultaneously. In one tank standard contaminant NH 4 Cl as per IEC 62217/IEC TR 62730 is used and in other tank acidic contaminant is used to simulate normal and acidic rain conditions. A comparative study is conducted on the insulator specimen under different environmental stresses to evaluate long term performance. The conductivity of both normal and acidic contaminants is kept 2.5 mS/cm approximately to observe the effect of acidic environment on long term performance. During the experimental duration of 1000 hours leakage current was regularly measured and recorded. Samples were visually investigated and degradation was found to be more under acidic environment and tracking was observed. After the experiment, physico-chemical analysis is conducted on the degraded samples. Fourier transform infrared (FTIR) spectroscopy is utilized to analyze the surface chemical changes on degraded insulators samples. Salt deposition was detected on aged samples in the FTIR spectrum. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDAX) were conducted to detect elemental presence over the surface of degraded/aged samples. Thermo-Gravimetric Analysis (TGA) is utilized to analyze thermal stability and loss of ATH fillers before and after aging experiment. [ABSTRACT FROM AUTHOR]

The proven reliability of ceramic cap-and-pin insulators for high voltage (HV) and extra-high voltage (EHV) overhead lines suffers in the presence of harsh industrial or strong salt pollution [1]. In these cases, apart from the countermeasures such as increasing creepage distance, washing, and applying greases, insulators with a silicone rubber surface have demonstrated better performance [2]. The two alternatives for having insulators with a polymeric surface are (1) composite insulators, which consist of an inner fiberglass rod and an outer silicone rubber housing, and (2) precoated toughened glass cap-and-pin insulators with room temperature vulcanized (RTV) silicone rubber coating, hereafter referred to as RTV insulators. [ABSTRACT FROM AUTHOR]

Silicone composite insulators are state of the art for outdoor applications. The development of these insulators has reached a high level so in a next step the weight of these insulators can be reduced. One way to do so is by adding a low-density filling material. In this paper, the thermal stability of silicones filled with hollow microspheres (HMS) with diameter in the micrometer range is examined. High thermal stability is a key property of outdoor insulation materials as it determines the resistance against arc discharges as well as erosion due to dry band discharges. Therefore, arc resistance tests, inclined plane tests and thermogravimetric analysis are used to investigate the influence of HMS on thermal stability of silicone. The influences of thermal material properties like heat conductivity, heat capacity and temperature conductivity are examined and a method to calculate heat conductivity of porous composite materials is discussed. Results show no influence of thermal material properties on thermal stability, thus observed decrease of thermal stability of silicone filled with glass HMS cannot be explained by thermal characteristics. Instead, increase of surface area of the silicone is identified as key parameter, which causes a stronger thermal degradation. In addition, application of glass HMS in liquid silicone rubber (VMQ1) hinders the curing and reduces thermal stability further. Adding of ceramic HMS and silanization of glass HMS decreases erosion and increases arc resistance. This can be explained by an increased interphase quality between the silicone and these fillers, which prevent accelerated thermal degradation due to an increased thermally active surface area of the silicone. [ABSTRACT FROM PUBLISHER]

ABSTRACT Hollow microspheres (HM) of ceramic, silica, and glass-filled silicone rubber (SR) composites were prepared, and the effects of hybrid HM on thermal and mechanical properties of composites were investigated. The results indicate that hybrid HM can effectively improve the thermal insulation property of HM/SR composites. Especially, for sample 15S, the thermal conductivity and thermal degradation temperature reached 0.1273 W/m K and 521 °C (45 °C higher than that of neat SR), respectively. Besides, thermal insulation performance was improved, showing as a temperature of 103.2 °C after 15 min heating, which is 37.8 °C lower than that of SR. The tensile strength of composites was enhanced from 1.92 MPa at 11.56 vol % hollow silica microspheres (HSM) loading to 3.08 MPa at 21.88 vol % HSM loading. Moreover, the compressive strength was improved from 3.33 to 5.68 MPa by introducing more hollow ceramic microspheres into the matrix, in this case, from 7.79 to 15.33 vol %. Furthermore, the failure mechanism was analyzed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46025. [ABSTRACT FROM AUTHOR]

Currently there are no international standards for evaluating the tracking and erosion resistance of DC polymeric insulation under contaminated conditions. Researchers often modify the existing AC inclined plane test standards such as the IEC-60587 to accommodate DC voltage conditions but this has been reported to give various inconsistences. This paper presents comprehensive experimental results on inclined plane tests of silicone rubber (SiR) insulation at 3.5 and 4.5 kV AC and positive DC using intravenous (IV) system as the pollutant supply. The leakage currents (LC) were recorded throughout the entire tests. In addition, various physiochemical tests namely, Fourier Transform Infrared analysis, thermo-gravimetric analysis, scanning electron microscopy and energy dispersive spectroscopy were performed on the aged and unaged samples. Results show that DC LC is bigger (about three times) than that under AC for the same equivalent voltages. Furthermore, DC LC variations are less random and the average magnitudes increase with duration of voltage application compared with AC. The physiochemical analyses show that 3.5 kV(rms) AC and 3.5 kV DC aged samples have comparable chemical characteristics albeit with electrode corrosion elements detected on the DC aged samples. Under 4.5 kV DC the degradation becomes significantly more severe and unrepeatable. It is therefore concluded that at 0.3 ml/min, pollutant flow rate, 3.5 kV positive DC and 3.5 kV(rms) AC are comparable as test voltages for inclined plane accelerated ageing of SiR insulation.

Field investigations of silicone rubber (SiR) insulators provide useful information about their performance. The field performance of SiR insulators depends on many factors, including electrical stress, and environmental and service conditions experienced. This paper provides a condition assessment of the housing material of five different types of 20 kV field-aged SiR insulators from the same manufacturer with different operating years and states. The assessment was performed through mechanical, electrical, and material techniques. The main objective of this paper is to investigate the aging behavior of SiR insulators, in order to predict their lifetimes. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) were utilized to quantify the degree of degradation. The mechanisms of the variations in mechanical properties for aged samples were also discussed. In a tensile test, the reduction of strain-to-break to 50% and in other tests the failure of insulators in salt fog chamber were used as the end of life criterion. Finally, the lifetime of the tested insulators was predicted based on the various aforementioned tests. [ABSTRACT FROM AUTHOR]

Insulators should be designed to perform both their electrical and mechanical functions, without failure or breakage. This paper aims to illustrate that a newly designed silicone shed with a nozzle requires no maintenance to remove mineral deposits. This new design takes advantage of the constant movement of air to remove the surface deposits that commonly cause erosion and collapse in insulators. This cleaning effect results from the passing air, which removes the deposited particles from the shed surface. This approach works well for a silicone-elastomer-coated shed with hydrophobic features. The results of laboratory experiments designed to reproduce the conditions of insulators in the field indicate that the downstream fluid speed is always higher than the upstream speed when air flows over the new silicone elastomer shed. This ensures that particle deposition on the sheds will be minimal, even over long periods. Furthermore, the silicone elastomers used to construct the sheds have high hydrophobicity which further prevents the deposited particles from sticking and facilitates easy cleaning via the air flowing around the insulators. [ABSTRACT FROM PUBLISHER]

The paper presents the experimental results of research on the effect of an external DC electric field on the coefficient of friction of silicone rubber (elastomer) during its rubbing against a steel surface in the "pin-on-disc" experimental set-up. In the tests there were used silicone rubber samples, the pure PAG and PAO synthetic base oils and their blends with an antiwear (ZDDP) additive. The coefficient of friction μ was determined under conditions with and without an external DC electric field. A DC electric field was generated between a silicone rubber sample and a rotating steel disc (a friction pair). A sample holder was electrically isolated from other metal parts of a tribometer and was connected to one of the poles of a DC power supply, while the other pole was connected by means of the carbon brushes to a rotating steel disc. The experimental results show that the external DC electric field established between the rotating steel disc and a silicone rubber sample causes the coefficient of friction to decrease. It was also found that the coefficient of friction μ depends on the steel disc's angular velocity n, the contact pressure p, and the type of base oil and its blends with the additive used. [ABSTRACT FROM AUTHOR]

With the fast development of high voltage DC (HVDC) cable, cable insulation under DC conditions has got more attention. In this paper, tests were conducted to study the electrical tree initiation in silicone rubber (SIR) under DC and polarity reversal voltages. It is found that electrical tree initiation has significant polarity effects under both DC and polarity reversal voltages. There are only single-branch-like trees and branch-like trees under DC and polarity reversal voltages. As for pre-stressing effects under polarity reversal, the pre-stressing voltage has positive effects to electrical tree initiation, while the pre-stressing time has little influence. Space charge distribution of SIR under high electric field was studied with flat plate pulsed electro-acoustic (PEA) system, and their characteristics were discussed to explain this phenomenon. Moreover, different treeing breakdown phenomenon is found under polarity reversal voltage which differs from that under DC voltage. The existence of fast charges and slow charges gives reasonable explanation to it. Special attention should be paid to the transient situation like polarity reversal which would result in irreversible effects more easily, and affect true length of life for HVDC cables. [ABSTRACT FROM AUTHOR]

A large number of silicone rubber (SR) insulators have been used in inland areas. Long-term performance evaluation, pre-ranking and selection of these insulators are highly significant. IEC and other institutes have proposed several 5000 h tests with multiple stresses to evaluate long-term performances of composite insulators. However, these procedures have their own characteristics and limitations. None of the existing tests could provide a satisfactory simulation of the condition with severe contamination and high non-soluble deposit density (NSDD) in inland areas as well as the hydrophobicity change process of SR insulators. Based on modifications of the IEC test procedure, a novel 5000 h test procedure is proposed. There are two main modifications. The first one aims to replace the salt fog with a mixed contamination fog including both soluble and non-soluble pollutants. The second one aims to provide sufficient time for SR to recover and to transfer its hydrophobicity. A set of test apparatus based on this novel 5000h test procedure was designed and constructed. Two tests were conducted on 16 SR insulators with different material compositions and shed designs, including an AC and a negative DC test. Contamination accumulation on the surfaces of the specimens during both tests were measured. The NSDD and equivalent salt deposit density (ESDD) were close to those measured in the field in contaminated inland areas. Hydrophobicity reduction and recovery were well reproduced. Discharge activities were observed and leakage current was measured, which were consistent with the hydrophobicity statuses of the specimen. Tracking and erosion were found for some specimens, and the damage pattern was the same with that found in the field. The poor material properties and inappropriate shed designs could be identified successfully through the test. It was concluded that the modified 5000 h procedure could provide a satisfactory simulation of the desired contamination condition and hydrophobicity change process, and the insulators with different design defects are successfully screened out. [ABSTRACT FROM PUBLISHER]

In recent times, high temperature vulcanized (HTV) silicone rubber (SIR) insulators featuring several advantages, have gained importance over conventional ceramic and glass insulators. However, environmental stresses and electrical discharge activities degrade their superior performance therefore long term reliability of polymeric insulators is still under investigation. In the present work, arid climate aging experiments are carried out on SIR and effects of dry thermal exposure on composite insulators are investigated. Hydrophobicity recovery phenomenon for contaminated polymeric insulator sheds is reported with elevated temperature and a method proposed for achieving uniformity in pollution layer is also highlighted. Furthermore, Fourier transform infrared (FTIR) spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Thermo-Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) techniques are utilized to assess and analyze the changes in the material properties. The consequence of arid heating on tensile strength of SIR is evaluated. Also the dry flashover studies are carried out to discern the concerns related to the effects on thermally aged SIR insulators due to sudden overvoltages occurring in transmission lines. [ABSTRACT FROM PUBLISHER]

Tensile and compressive stress, produced by the spring clamp device and the banding force after the expansion of silicone rubber stress cone, can affect the electrical properties of silicone rubber in the cable accessories. Electrical tree, one of the main electrical aging phenomena, is supposed to be related to the mechanical stress. In this paper, the treeing growth characteristics considering the tensile and compressive stress were investigated by the pin-plane electrode system respectively. The tensile rate of silicone rubber ranged from 0% to 30%, while the compressive rate varied from 0% to 50%. The results indicate that both the tensile stress and compressive stress affect the treeing propagation characteristics. The appearance probability of bush tree increases and it becomes the main tree structure at higher tensile rate, while branch tree turns into the main tree structure at higher compressive rate. Electrical tree initiation probability becomes higher and the initial time tends to be shorter under the tensile stress, while they show an opposite tendency under the compressive stress. Under tensile stress, the tree length, fractal dimension and accumulated damage become lager as the tensile rate increasing, which indicates that the higher tensile rate accelerates the treeing process. However, under the compressive stress, the treeing growth process shows a converse trend, which demonstrates that the higher compressive rate retards the electrical tree growth. [ABSTRACT FROM PUBLISHER]

High temperature vulcanized (HTV) silicone rubber (SiR) is widely used as HVDC cable accessory insulation considering its outstanding electrical properties along with elasticity and thermal resistance. However surface charge caused by corona would accumulate on SiR surface and distort the local field which in consequence led to accessory premature discharge and insulation failure. This paper focused on the behavior of surface charge of SiR composites and managed to modify it by incorporating silicon carbide (SiC) particles into SiR matrix. The content of SiC varied from 0 to 100 % and its effects on the field-dependent conductivity and surface charge behaviors were discussed. The outcomes of experiments showed that the SiR/SiC composites performed a nonlinear conductivity as a function of electric field when the content of SiC exceeded 30 %. It was also noticed that this field-dependent conductivity became more obvious when the content of SiC increased. Meanwhile, the decay rate of surface charge was observed to rise with the increase of SiC content and voltage. It was confirmed that the SiR/SiC composites could accelerate the decay of surface charge and increase the dc conductivity under high voltage, resulting from the modification of the trap level distribution. [ABSTRACT FROM PUBLISHER]

In recent times, high temperature vulcanized (HTV) silicone rubber insulators (SIR) are being widely used for overhead high voltage transmission and distribution systems. However, over a period, the insulator surface will be exposed to high temperature in several places, particularly in desert areas; further accumulation of pollutants can alter the temperature distribution along the insulator. In the present work, long-term electrothermal experimentation is carried out on various types of full-scale insulator units. The effect of temperature on pollution performance of SIR insulators is studied, and a novel and simple methodology to achieve uniform contamination layer on inherently hydrophobic HTV SIR insulator samples is presented. A specially fabricated oven having a provision for high voltage connection and facility for measurement of leakage currents is provided. Furthermore, study of migration of low molecular weight, recovery trends of hydrophobicity, and changes in material properties using scanning electron microscopy Fourier transform infrared spectroscopy is carried out. [ABSTRACT FROM PUBLISHER]

A study was conducted to evaluate new and laboratory-aged samples of surge arresters and anchorage polymeric insulators, for 12 and 24 kV networks, which are used by the Rio Grande Energia (RGE). Power Utility Polymeric compounds were analyzed by Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TG), Dynamic-Mechanic Analysis (DMA), Fourier Transformed Infrared Spectroscopy (FTIR) and Scanning Electronic Microscopy (SEM) to verify changes in the insulator properties due to degradation occurred during the experiments. The analyses were carried out before and after 6 months of aging in laboratory devices (weatherometer, 120 °C, salt spray, immersion in water). After the aging experiments, high-voltage electrical tests were also conducted: a radio interference voltage test and, simultaneously, the total and the internal leakage currents were measured to verify the surface degradation of the polymeric material used in the housing. The impulse current test was applied with current values close to 5, 10 and 30 kA, in order to force an internal degradation. Results showed that only surface degradation is detected at the polymer. The main properties of the parts were not affected by the aging. It confirms that polymer insulator and surge arrestor are appropriate for use in electricity distribution networks.

Surface potential decay characteristics of specimens extracted from in-service aged and reference HVDC composite insulator sheds are reported and analyzed in this paper. In the experiments, surfaces of the insulator samples were charged by dc corona and the decay was recorded utilizing a non-contact technique. In addition, surface and bulk conductivities of the specimens were determined and used for analyzing by means of computer simulations their impact on the potential distribution profiles and its decay. Based on the performed experiments, trap density distributions, mobility of charge carriers and field dependent bulk conductivities are deduced for the investigated samples with the aim to evaluate the ageing severity. [ABSTRACT FROM AUTHOR]

Discharges caused by water droplets on the surface of polymeric insulators can affect the long-term reliability of the component by lowering the surface hydrophobicity boosting surface discharges. The main objective of this work is to quantify the effect of different types of water drops arrangements, their position and dry bands width on the flashover voltage of the silicone insulating surface with non-uniform electric field systems. The tests were done on a rectangular sample under AC voltage. Water droplets with different conductivities and volumes were placed on the silicone rubber surface with a micropipette. A rod-rod electrode system is used. The findings of this work indicate that the performance of the samples decreases with the presence of water drops on their surfaces. Further, these experimental findings show that there is a limiting number of rows from which the flashover voltage of the insulation is minimal and constant. This minimum is a function of the distance between two successive rows. Finally, it is concluded that the system withstand voltage increases when the row of droplets on the electrode axis is removed. [ABSTRACT FROM AUTHOR]

This paper analyzes silicone rubber housing materials that have been aged in service in 200 kV and 400 kV transmission line systems in the Gulf region. Non-uniform discoloration with traces of white residue are more evident across the upper and lower sides of the 400 kV as compared to the 200 kV sheds located near both the energized and the ground ends of the insulators. Scanning electron microscopy (SEM) showed an increase in the roughness for all the surfaces of the materials analyzed as compared to the bulk. Surface oxidation was indicated by the increase in the Oxygen/Carbon (O/C) ratio determined using energy dispersive X-ray (EDX) and the existence of the silanol groups (Si-OH) as detected in the Raman spectroscopy. The effect of electric field causing surface discharges oxidizing the surface was more evident on the 400 kV as compared to the 200 kV materials, particularly on the lower side of the sheds located near the energized end of the insulators. The effect of photo-oxidation due to ultra violet radiation appears to be increasing as compared to the electric field enhancement on the upper side of the sheds, particularly for those located near the ground end of the insulators. Thermogravimetry analysis is found useful in indicating the relative amount of alumina tri-hydrate filler and the polymer in the silicone rubber housing composition. Both O/C ratio determined using EDX and the silanol groups detected using Raman spectroscopy are proposed as reliable aging indicators to assess the condition of the silicone rubber surfaces that have been aged in service under relatively light polluted conditions. Raman spectrometry has the additional advantage as portable Raman spectrometers can be used to conduct field measurements on site. [ABSTRACT FROM AUTHOR]

The presence of water droplets on the surface of insulators provides intensification of the electric field, which are caused by the non-uniform voltage distribution and dielectric properties of the different materials. The degree of Electric field (E-field) intensification at the triple joint, the region where water, the non-ceramic dielectric and the air are in contact, must be carefully analyzed, because under certain conditions, breakdown voltages can be reached, sometimes, under very little or no contamination at all, which can cause the insulator wettability, tracking, flashover and degradation. In this paper, variations of the electrical field over two polymer compounds widely used in the insulator manufacturing industry, Silicone Rubber (SIR) and High Density Polyethylene (HDPE), are analyzed on a 2D geometry with respect to contact angles of constant volume water droplets. The Electrical field is also computed as a function of relative water droplets distances. [ABSTRACT FROM AUTHOR]

High temperature vulcanized (HTV) silicone rubber (SiR), due to its excellent electrical insulation, elasticity and temperature resistance, is used in cable accessories for HVDC cables. The space charge, generated under dc stress in SiR, would distort the local electric field, further influencing the characteristics of partial discharge and accelerating the insulation aging. This paper tried to modify the space charge behaviors of HTV SiR composites by incorporating silicon carbide (SiC) particles into the polymer matrix with the filler content of 10, 30, 50, 100 wt%. The effects of the SiC particle content on the field-dependent conductivity and the space charge behaviors of HTV SiR were studied. The conductivities under different electric fields were measured by a three-electrode system at room temperature and the space charge behaviors were observed by the pulsed electro-acoustic (PEA) method. The results indicated that the conductivity of SiR/SiC composites was a nonlinear function of electric field when the content exceeds 30 wt%. With the increase of filler content, the threshold field for nonlinear conductivity decreased and the nonlinear coefficient increased. Meanwhile, the amount of space charges was dramatically reduced. It is suggested that the SiR/SiC composites with nonlinear conductivity can improve the dc conductivity under high electric field, thus raising the carrier mobility and suppressing the accumulation of space charge. [ABSTRACT FROM PUBLISHER]

Silicone rubber insulators are replacing the conventional ceramic and porcelain insulators rapidly in power transmission and distribution industry. Very limited field knowledge is available about the performance of silicone rubber insulators in polluted and contaminated environments and therefore need further investigation. A comprehensive analysis of silicone rubber sheets (intended for coating outdoor insulators) was carried out in this paper based on experimental results. The main performance parameters analyzed were arc inception voltage and flashover voltage. Dependence of these parameters on equivalent salt deposit density (ESDD), non-soluble salt deposit density (NSDD), relative humidity, ambient temperature, fog rate, dry band formation, dry band location and number of dry bands were investigated extensively. Insulator orientation and its effect on performance were also studied. The authors believe that this paper will provide a comprehensive knowledge about the flashover characteristics of silicone rubber insulators under humid, contaminated and dry band conditions. These results could be used in the selection and design of silicone rubber insulators for polluted environments. [ABSTRACT FROM AUTHOR]

HTV silicone rubber (SiR), due to its better electrical insulation, elasticity, temperature resistance, is used in cable accessories for HVDC cables. The space charge, formed under dc stress in SiR, would distort the local electric field, and furtherly influence the characteristics of partial discharge and accelerate the insulation aging. Direct fluorination, as a solution to change the chemical component, could alter the electrical properties of the polymer surface layer. This paper focuses on the effect of the fluorination on the space charge accumulation in HTV SiR. In this investigation, the samples were fluorinated at 25 ° using a F2/N2 mixture gas with 20 % F2 by volume at 0.05 MPa for 10, 20, 30 and 40 minutes. The space charge behavior of the fluorinated samples was observed by PEA method and the trap level distribution was obtained by modified isothermal discharge current (MIDC) test. The results indicated that the fluorination for 20 minutes effectively suppressed the space charge injection in SiR. However, excessive fluorination (over 30 minutes) brought in abundant deep traps, and led to significant amount of space charge accumulation in the bulk of polymer. As a consequence, the appropriate fluorination has significant effect on the space charge accumulation in HTV SiR and has a potential application for inner insulation in premolded accessories of HVDC cable. [ABSTRACT FROM AUTHOR]

Partial coating of insulators with semiconductive silicone rubber has proved to be a potential method for reducing ice accretion on insulators. The performance of the coated insulator strings is mainly determined by the insulator parameters, the coating resistance, and the coating area covering the insulator surface. This research is to investigate the effect of using semiconductive silicone rubber coating on the anti-icing performance of ceramic insulators, considering the coating resistance and the coating area. A series of icing tests was carried out in a climate room and the results obtained from tests on a single insulator unit were extended to short insulator strings. The experimental results showed that the magnitude of the appropriate coating resistance was below 0.3 ~M\Omega in the freezing condition recommended, and that the suitable width of the band of the uncoated area was about 5 to 8 cm. Since the main heating power was consumed in the region of the uncoated band, the uncoated area should better be close to the edge of the top surface of the insulator, in which case the icicles could fall off more easily. [ABSTRACT FROM PUBLISHER]

Silicone rubber has been widely used for electrical insulation in several power devices, e.g.: power insulators and metal-oxide surge arresters. In accordance with international standards, High-Temperature-Vulcanization Silicone Rubber for electrical power insulation should support 3.0 kV in electrical tracking and erosion tests, which are well established by the IEC. However, most of silicone rubbers used for manufacturing of electrical power components supports a maximum voltage of 2.75 kV. This research proposes a careful evaluation of the electrical performance of a new 6.0 kV silicone rubber developed by a worldwide-known manufacturer in the electrical power segment. The new silicone rubber is submitted to electrical tracking and erosion tests using two different approaches described in the IEC 60587: the step and steady methods. These two testing procedures are carried out in AC, following the normative recommendations, and also adapted for DC analyses. This research presents three principal contributions: a testing methodology considering both AC and DC, important conclusions on an emergent technology for electrical insulation in power systems and a quantitative analysis of erosion in polymeric composites based on the mass loss. [ABSTRACT FROM AUTHOR]

Phosphorus-based flame retardants—ammonium polyphosphate (APP), aluminum diethylphosphinate (ADP) and octaphenyl polyhedral oligomeric silsesquioxane (OPS)—were incorporated into room temperature vulcanized (RTV) silicone rubber insulating composite, in order to study the influence of flame retardants (FRs) on the ablative and flame-retardation properties of the RTV silicone rubber composites. The results showed that the FRs remarkably improved the ablative and flame-retardation properties of the RTV silicone rubber composites. With the addition of APP, ADP or OPS alone, the linear rate of the RTV silicone rubber composite was reduced by about 16.4%, 26.0% and 17.1%, respectively. In addition, the FRs obviously improved the flame retardancy, smoke suppression and thermal stability, based on a cone calorimetry test. The peak heat release rate (p-HRR) for the pure RTV silicone rubber composite was 338 kW/m 2 . This was reduced to 217 kW/m 2 , 184 kW/m 2 and 196 kW/m 2 with the addition of APP, ADP and OPS, respectively. Moreover, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and thermogravimetric analysis tests showed that the FRs are helpful in forming a denser and intact char layer, due to enhanced condensed phase flame retardancy action. Furthermore, APP or ADP combined with OPS exhibit a significant synergistic effect in improving the overall performance of RTV silicone rubber composite. Specifically, the linear ablation rate (0.079 mm/s) was reduced by 45.9% with 15 wt. % ADP and 10 wt. % OPS in the RTV silicone rubber composite. [ABSTRACT FROM AUTHOR]

We have used for the first time a composite consisting of few-layer exfoliated graphene and electrically conducting polyaniline (PANI) as the ion-to-electron transducer (solid-contact) in Ca 2+ -selective solid-contact electrodes (CaSCISEs). The drop cast transducer deposited from the graphene–PANI dispersion in N -methylpyrrolidone makes use of the synergistic effect of these two materials. It maintains the ion-to-electron transduction which is characteristic for the electrically conducting polymers (ECP), but in addition, graphene improves the reproducibility of the standard potential of the SCISEs compared to the neat PANI based electrodes and increases the hydrophobicity of the transducer (ca. 30° higher water contact angle) which counteracts the water layer formation. Our results reveal that the incorporation of few-layer graphene in the transducer layer improved also the initial potential stability and the response characteristics of the CaSCISEs due to the electrocatalytic effect of the graphene–ECP composite, which facilitates the electron transfer at the transducer/substrate interface. We obtained a potential reproducibility of only ±4 mV ( n = 3) for the CaSCISEs having graphene–PANI as the solid-contact. The CaSCISEs in this study had a detection limit of 5 × 10 −8 M Ca 2+ , which was obtained without any sophisticated pre-treatment protocols. [ABSTRACT FROM AUTHOR]