Silicone Rubber Insulators Research Articles

Inclined Plane Test for Erosion of Polymeric Insulators under AC and DC Voltages

In this paper a study on effects of AC and DC dry band arcing on silicone rubber insulators surface is presented. The insulators tested are commercially available, having as their main material silicone rubber with alumina trihydrate as an additive. In addition to literature analysis, experiments were performed following the inclined plane test method described in the ASTM D2303. It was found that the voltage type (AC or DC) and polarity (positive or negative) influence not only the damage caused by the dry band arcing, but also the average value and the behavior of the leakage current. The voltage type that caused the most damage on the insulating material was DC with positive polarity, followed by DC with negative polarity, then AC. According to other studies, the difference in the results obtained with different voltage types are mainly caused by the ion release on the electrodes, behavior of the contaminant under the electric field and the length and duration of the dry band arcs. This shows that silicone rubber insulators should not be utilized in DC systems with same voltage as the ones that are designed to withstand AC, unless modifications are made in the material properties or in the insulators design.

Forecasting Flashover Parameters of Polymeric Insulators under Contaminated Conditions Using the Machine Learning Technique

There is a vital need to understand the flashover process of polymeric insulators for safe and reliable power system operation. This paper provides a rigorous investigation of forecasting the flashover parameters of High Temperature Vulcanized (HTV) silicone rubber based on environmental and polluted conditions using machine learning. The modified solid layer method based on the IEC 60507 standard was utilised to prepare samples in the laboratory. The effect of various factors including Equivalent Salt Deposit Density (ESDD), Non-soluble Salt Deposit Density (NSDD), relative humidity and ambient temperature, were investigated on arc inception voltage, flashover voltage and surface resistance. The experimental results were utilised to engineer a machine learning based intelligent system for predicting the aforementioned flashover parameters. A number of machine learning algorithms such as Artificial Neural Network (ANN), Polynomial Support Vector Machine (PSVM), Gaussian SVM (GSVM), Decision Tree (DT) and Least-Squares Boosting Ensemble (LSBE) were explored in forecasting of the flashover parameters. The prediction accuracy of the model was validated with a number of error cost functions, such as Root Mean Squared Error (RMSE), Normalized RMSE (NRMSE), Mean Absolute Percentage Error (MAPE) and R. For improved prediction accuracy, bootstrapping was used to increase the sample space. The proposed PSVM technique demonstrated the best performance accuracy compared to other machine learning models. The presented machine learning model provides promising results and demonstrates highly accurate prediction of the arc inception voltage, flashover voltage and surface resistance of silicone rubber insulators in various contaminated and humid conditions.

Optimized Portable Unilateral Magnetic Resonance Sensor for Assessing the Aging Status of Silicon Rubber Insulators

Silicone rubber insulators (SRIs) play an important role in high-voltage power transmission lines. Given that SRIs critically threaten the safe operation of the power grid, quantitatively assessing the aging status of SRIs in situ is crucial. In this article, a portable unilateral magnetic resonance (UMR) sensor with a U-shaped magnet structure and its measuring circuit were designed for the nondestructive detection of the aging status of SRIs in situ. First, the optimization efficiency of the magnet structure was improved through a uniform design method. Then, the planar radio frequency (RF) coil was designed by the finite-element method. Furthermore, the demagnetization effect of eddy currents induced in metal materials on the RF magnetic field was analyzed. We measured the SRI sheds at different service times and obtained the corresponding 1H transverse relaxation decay curves by importing the Carr- Purcell-Meiboom-Gill (CPMG) sequence. Finally, the transverse relaxation decay curves were postprocessed using inverse Laplace transformation, and the 1-D spectrum distributions of transverse relaxation time (T2) were obtained. The results reveal that T2 of the surface of the SRI shed decreases as the service time of the SRI increases. In addition, the difference in T2 between the surface and interior of the SRI shed increases. The comparison experiments demonstrate that the U-shaped sensor designed in this article is superior to the curved sensor previously designed by our team. The effect of temperature variation on SRIs aging assessment was considered at last.

Fabrication of self-cleaning superhydrophobic silicone rubber insulator through laser texturing

ABSTRACT Silicone insulators are gaining its importance in the transmission and distribution of the power system networks. This study proposes a simple and high throughput way of fabrication of superhydrophobic silicone surfaces. The Nd:YAG nanosecond pulse laser was used to engrave six different types of structures on silicone rubber. The water contact angle (CA) and contact angle hysteresis (CAH) were measured using drop shape analyser goniometer. The self-cleaning property of the structured silicone surfaces was tested. Among six types of patterns, the structures formed through 50% scanning overlapped possess high CA (159 ± 1°) with very low CAH (3°) which is desirable for any self-cleaning surface. However, a completely irradiated silicone surface gives the highest CA (163 ± 2°) with very high CAH (61.84°). The proposed work is a vital step towards making a superhydrophobic insulator surface without the use of any coating for high voltage power system applications.

Understanding performance of transmission and distribution insulators at very low temperature conditions

Polymeric or silicone rubber insulators are extensively used for high-voltage transmission by electrical utilities due to advantageous features like lightweight, better contamination performance, etc. The performance of silicone rubber insulators exposed to low temperature conditions with continuous application of electric stress is of utmost importance as these insulators are being used under such climatic conditions in the country. In the present work, long-term experimental investigations have been conducted for 1000 h at 0 °C and for 1500 h at − 20 °C with application of electrical stress to simulate near-field conditions. A special experimental arrangement has been established for the investigations. Leakage current was monitored at regular intervals, and further material evaluation techniques like Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDAX), mechanical strength measurements, etc., were conducted before and after the experimentation to verify the surface degradation on the polymer insulators. Some interesting results obtained during the experimentation for normal and polluted conditions along with the analysis carried out are presented.

Effect of accumulated surface charges on DC flashover of SiR insulators under pollution and aging conditions

In this paper, the measurements and modeling of the DC flashover behaviors of silicone rubber (SiR) insulators under pollution and aging conditions in the presence of surface charges have been presented. For this purpose, four different types of standard HTV-SiR insulators were selected, and then, DC flashover performance was carried out on the studied insulators in the three states including non-aged, aged, and contaminated conditions in the presence surface charges. The surfaces of the insulators were charged by an external corona source in the experimental tests, and then, the surface electric charges were measured. The experimental results of DC flashover voltage showed that the positive and negative surface charges affected flashover performance in all the states. Based on obtained empirical models of the DC flashover performance, it can be concluded that the increased aging time, positive electric charges, pollution, and average diameter reduced DC flashover performance, while the ratio of shed spacing to shed depth and negative charges enhanced the flashover voltage level.

Influence of snow accretion on arc flashover gradient for various types of insulators

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.

Sequential RTV/(TiO2/SiO2) nanocomposite deposition for suppressing the leakage current in silicone rubber insulators

The sequential deposition method is introduced for suppressing the leakage current in silicone rubber insulators. Room temperature vulcanizing silicone and TiO2/silica nanocomposites are sequentially deposited on silicone insulators surface. TEM results showed that TiO2 nanoparticles size is about 20–30 nm, and the structural study revealed their anatase crystalline structure. Silica nanoparticles are deposited on the surface of insulators by spray deposition. The contact angle was enhanced from 104° to 149° after nanoparticles deposition, which confirms the hydrophobicity improvement. Results show that leakage current for nanocomposite samples in a contaminated environment reduced to about 0.02 mA, which was 1 mA in insulators without any coating, indicating a remarkable improvement after coating. The stability of bare and coated insulators was examined under kaolin, salt, NH4Cl-contaminated environment, and also UV radiation for more than 500 h. Results show that the sequential deposition could be utilized as a cost-effective and scalable method for enhancing the hydrophobicity and stability of insulators.

DC and AC electric field analysis and experimental verification of a silicone rubber insulator

This paper presents the electric field analysis as well as the experimental verifications of a silicone rubber insulator by considering DC and AC voltage conditions. As a first step, a 3D electric field simulation of the insulator was performed by using a commercially available software based on finite element method. DC voltage and 50 Hz power–frequency voltage simulations were conducted for the given insulator. Low frequency field distribution along the insulator has been investigated to find threshold frequency values for resistive and capacitive field regions. The effect of the conductivity of air surrounding the insulating system on the electric field was evaluated. For each condition, electric potential and field distribution along the creepage path of the insulator was obtained. In addition to the simulation studies, voltage measurements under AC and DC conditions utilizing a different approach for the silicone rubber insulators were conducted on the insulator by using a non-contact type electrostatic voltmeter to validate the simulation results.

Comparison of AC Flashover Performance of Snow-Accreted Insulators Under Natural and Artificial Simulation Environments

The research on snow-accreted insulators have been performed in an artificial climate chamber. However, the differences in the distribution, density and compactness of snow accretion under natural and artificial simulation environments cause differences in the flashover performance of snow-covered insulators. In the present work, a series of flashover tests were conducted on snow-coated glass and silicone rubber insulators in the climate chamber and at Xuefeng Mountain Natural Icing Test Base. The discrepancies in the electrical characteristics and flashover process of snow-covered insulators under two test environments were compared and analyzed. Results show that the arc flashover gradient of snow accreted insulator at high altitude site is higher than that in the laboratory because of the differences of the environmental parameters. Affected by the adiabatic effect and capillary action of snow layer, within the range of the study the flashover gradient of insulators covered with snow increases with the increasing in the snow thickness. The calculation of various forces applied on arcs during its propagation demonstrates that when the arc current is less than 0.2 A, the local arcs develop along the snow surface of the insulators under the action of an electrostatic force. As the current increases beyond 0.2 A, the thermal buoyancy is predominant, thereby causing arcs to levitate from the insulator surface.

AC Flashover Voltage Model for Polluted Suspension Insulators and an Experimental Investigation in Salt Fog

In recent years, the electrical performance of polluted suspension insulators operating in coastal foggy regions has attracted wide attention because of the occurrence of flashover. Surface wetting by salt fog accretion increases the surface conductivity and degrades the flashover voltage of insulators. Normally, the effect of conductivity under fog condition and pre-contamination on the flashover of polluted insulators are analyzed separately. Therefore, this does not reveal the flashover characteristic in salt fog, which requires further research. This paper describes salt fog experiments with an AC test voltage conducted using suspension insulators in a 110-kV power system. The electrical strength performance of insulators with salt fog treatments is analyzed, and the effects of salt deposit density (SDD) and the fog water conductivity (FWC) on the flashover of three types of suspension insulators are studied. The concept of additional SDD is proposed to quantify analyze the effects of salt fog. The results show that there is less dependence on FWC at higher pollution levels than at lower pollution levels. That is, the effect of FWC on 50% AC flashover voltage ($U_{50}$ ) can be neglected for SDD >0.15 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , whereas FWC has a strong effect on $U_{50}$ for SDD <; 0.15 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . FWC has a greater influence on $U_{50}$ of ceramic insulators than on that of silicone rubber insulator. A model for calculating the critical flashover voltage of insulators is proposed by considering the combined effect of FWC and pre-polluting SDD.

Performance analysis of silicone rubber insulator in DC high-voltage inclined plane tracking test

The present trend in electric power transmission technology evolves with the latest high-voltage direct current (HVDC) transmission network. Silicone rubber (SiR) composite insulators are predominantly used since two decades for high-voltage alternating current (HVAC) transmission lines. In case of HVAC transmission line, the performance of SiR insulators is promising; however, there are failures reported with their uses for HVDC transmission line. In this research work, SiR composite formulations are varied to study their effective changes in the direct current (DC) tracking and erosion resistance. Four different weight percentage (wt%) aluminum trihydrate (ATH) fillers loaded SiR formulations are prepared and invariably subjected to positive polarity DC inclined plane tracking (DCIPT) test before and after ultraviolet (UV) aging. The Fourier transform infrared spectroscopy study has been carried out to understand their morphological changes after and before UV aging. The results of these tests indicated that DC tracking and erosion resistance effectively reduced severe surface degradation for UV-aged SiR material. However, the 40 wt% ATH-filled SiR sample performed well exhibiting higher time to failure in positive DCIPT and thus could be better usable as HVDC insulation material.

Reliability assessment of aged SiR insulators under humidity and pollution conditions

In this paper, the effect of different pollution and humidity variations on the reliability of aged Silicone Rubber (SiR) insulators are investigated. Firstly, four different types of 20 kV SiR insulators have been selected to evaluate the effect of different insulator profiles on Flashover Voltage (FOV). Then artificially accelerated aging tests with 1000 h duration have been conducted for the aging of insulators. Numerous FOV tests have been carried out on the aged SiR insulators under different humidity and pollutions. Next, the risk of insulators utilization under different ambient conditions have been calculated by using the experimental test's data. Finally, the reliability of insulators under different conditions have been calculated and a new mathematical model for the reliability in different humidity has been proposed. The effect of SiR insulator profiles on FOV has been studied and the results have been shown that lower FOV is related to insulators with thicker profiles as well.

Investigation of Surface Degradation of Aged High Temperature Vulcanized (HTV) Silicone Rubber Insulators

Polymeric composite insulators are subjected to varying work conditions like rain and heat, which create an impact on degradation during their long service period. Electrical tracking under the Alternating Current (AC) field plays a predominant role in surface degradation, which can be different for fresh and aged insulations. The tracking studies on the fresh and aged polymeric insulation therefore become significant. Motivated by this, an indigenous low-cost electrical tracking setup was developed, and the tracking studies were carried out as per International Electro technical Commission standard (IEC) 60587 on fresh, thermal-aged and water-aged silicone rubber samples. Contact angles of samples were measured to analyse the effect of ageing on hydrophobicity. Further, to analyse the influence of ageing on insulation integrity, tracking tests were conducted and parameters like leakage current pattern and magnitudes, tracking length and loss of weight in the material due to tracking were examined. The physicochemical impacts of ageing on the surface degradation of the samples were also analysed using X-ray diffraction analysis and Fourier Transform Infrared Spectroscopy analysis. The investigations added insight into the degradation mechanism of polymeric insulators in terms of their electrical performance and physicochemical changes in the material. Comparison of these changes showed that ageing could influence surface degradation of samples.

A Three-Dimensional Analysis of Silicone Rubber Insulators Under Different Environmental Conditions Considering the Corona Rings Effect

A Three-Dimensional Analysis of Silicone Rubber Insulators Under Different Environmental Conditions Considering the Corona Rings Effect

Effects of algae contamination on the hydrophobicity of high‐voltage composite insulators

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.

Improvement of Electrical Insulation in Silicone Rubber by Adding Al2O3

Polymer Nano composite in recent time has shown high improvement in mechanical, chemical and electrical properties. Granting all these, the use of polymer nano-composites has only recently begun starting explorer. In recent times, polymer materials has shown remarkable improvement in electrical insulation because of their numerous advantages in out-door insulation systems because of their negligible weight, better pollution performance, low cost, good dielectric properties with easy processing. In polymer materials, silicone rubber is one of the lead polymer currently used and has high ending properties like high voltage insulator, thermal stability, excellent UV resistance and hydrophobicity. Therefore, Silicone rubber with fillers can overcome few drawbacks such as low strength and insulating properties.Oxides with different properties can help silicone rubber to enhance its properties. Oxides such as alumina, zirconia are being widely used in silicone rubber. Alumina which has strong thermal conductive and compressive strength with good electrical is used in silicone rubber. Here Silicone rubber nano composites are prepared by incorporating Al2O3 nano partic les. Electrical, Chemical properties like NaCl, HCl, and corrosion tests were conducted to know the performance of silicone rubber insulation at pollutant conditions. Dielectric tests were also done to know whether Al2O3 has made any effect with silicone rubber. Tensile strength and Hardness test were carried out to determine mechanical strength of the rubber.

Analysis of leakage current characteristics during aging process of SiR insulator under uniform and longitudinal non-uniform pollution conditions

This paper presents the comprehensive analysis of Leakage Current (LC) of a silicone rubber insulator under uniform and longitudinal non-uniform pollution conditions based on a large amount of test data. The experimental tests are carried out under different humidity levels for un-aged and aged samples. The results obtained indicate that the LC harmonics magnitudes increase with increasing the salt deposit density, aging time, and humidity, while they decrease with increasing the pollution non-uniformity degree. The analysis of phase angle difference between LC and applied voltage (θI-V°) demonstrates that the θI-V° is in the range of 54.3°–60.4°, 20.1°–32.5°, and 7.5°–11.8° under clean condition, light pollution and moderate pollution conditions, respectively. In addition, the θI-V° is less than 2.3° under heavy pollution condition. The non-uniformity of pollution distribution and insulator aging time have very little effect on the θI-V°, while the increase of humidity leads to a slight decrease in the θI-V°.

Flash-over voltage prediction of silicone rubber insulators under longitudinal and fan-shaped non-uniform pollution conditions

This paper proposes an Artificial Neural Network (ANN) model for AC flash-over voltage prediction of Silicone Rubber (SiR) insulators based on the experimental tests. In flash-over tests, the flash-over voltages of four different types of SiR insulators are measured under the uniform, longitudinal non-uniform, fan-shaped non-uniform and combined longitudinal, and fan-shaped non-uniform pollution conditions. The proposed ANN model is designed with six inputs data (insulator geometry and pollution parameters) and one output data (flash-over voltage). In order to validate the model, three different types of SiR insulators are tested under different pollution conditions. Then, their flash-over voltages are predicted using the proposed ANN model. The validation of the model shows that the absolute values of relative errors between flash-over voltages of test and prediction are less than 6%. This indicates a high efficiency of ANN technique in the flash-over voltage prediction of SiR insulators.

Research on Thermal Aging Characteristics and Mechanism of the Silicon Rubber Insulation Layer of Cable Joints

In order to solve the thermal aging problem of silicone rubber insulation layer of 220 kV integral prefabricated cable joints, the mass loss and thermal gravimetric (TG) were tested. The thermal aging mechanism of thermal degradation reaction of silicone rubber molecular chains was analyzed by gel content test and infrared spectrum test (IR). The results showed that the cross-linked network of the molecular chain structure gradually deteriorates, resulting in the increase of mass loss rate and the decrease of thermal stability. The results also showed that the increase of dual peak of differential thermal weight (DTG), the decrease of initial decomposition temperature and the remaining mass. With increasing aging temperature and aging time, the aging would be accelerated. These properties could reflect the degree of thermal aging of silicone rubber insulation layer. The results could also provide theoretical support for the preparation, operation and maintenance for silicone rubber cable joints.