Outdoor Insulators Research Articles

Deep Learning in High Voltage Engineering: A Literature Review

Condition monitoring of high voltage apparatus is of much importance for the maintenance of electric power systems. Whether it is detecting faults or partial discharges that take place in high voltage equipment, or detecting contamination and degradation of outdoor insulators, deep learning which is a branch of machine learning has been extensively investigated. Instead of using hand-crafted manual features as an input for the traditional machine learning algorithms, deep learning algorithms use raw data as the input where the feature extraction stage is integrated in the learning stage, resulting in a more automated process. This is the main advantage of using deep learning instead of traditional machine learning techniques. This paper presents a review of the recent literature on the application of deep learning techniques in monitoring high voltage apparatus such as GIS, transformers, cables, rotating machines, and outdoor insulators.

Overhead Lines and Wildfires: Role of Outdoor Insulators: Prepared by a Task Force of the IEEE DEIS Outdoor Insulation Technical Committee

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

Performance of a nanotextured superhydrophobic coating developed for high-voltage outdoor porcelain insulators

We live in an era of striking advancements in various domains of science and technology, where separate fields and specializations are overlapping into new horizons. This cooperative approach is emerging rapidly in polymer science by employing the organic and physical chemistry, materials science, as well as electrical and mechanical engineering to collaborate and develop uniquely innovative materials. In outdoor high voltage power equipment, various problems such as flashover, rain, icing, pollution, and UV can compromise the performance of insulators thereby distorting the reliability of the entire system. Superhydrophobic coatings are sought-after candidates owing to their ultra-non-wettable, easy-to-clean, and anti-ice character. However, the performance of superhydrophobic coatings when they are subjected to high-voltage fields is still lacking sufficient research. Here, we aimed at designing a robust and novel non-fluorinated superhydrophobic coating in order to increase the effective life-span of high-voltage insulators by preventing and/or delaying the possible arcing and flashover driven damages. The electrical properties of the coating were investigated through various and comprehensive test methods. The coating showed high thermal and desirable weathering stability. Compared with bare porcelain in dry, wet, and polluted conditions, the superhydrophobic coating successfully increased the flashover voltage. Moreover, the superhydrophobic coating exhibited low leakage currents through the condensation test when exposed to high humidity conditions. With leakage currents of as low as 20 mA after three continuous steps of voltage increase, the superhydrophobic coating showed less tracking and erosion lines than the pristine coating in an adapted inclined plane test for thin films.

Stress Control for Polymeric Outdoor Insulators Using Nonlinear Resistive Field Grading Materials Operating Under Different Conditions

Strong electric field enhancements near both end fittings of the high-voltage polymeric outdoor insulator contribute to premature degradation and aging. Nonlinear resistive field grading composites offer a promising possibility to stress control and more competitive products, especially with the increasing power density and voltage levels. Recently, new nonlinear resistive field grading materials (FGMs) based on zinc oxide (ZnO) microvaristors offer superior characteristics that enable using them in high-voltage systems. Moreover, their switching parameters can be tailored across an extensive range for a given application. This article discusses the effectiveness of nonlinear FGMs based on ZnO microvaristors for stress control along a 230-kV polymeric outdoor insulator using the finite-element method and COMSOL Multiphysics. Investigations are conducted to appropriately find out the electrical properties of the nonlinear FGMs to get an effective stress control along the insulator surface. The different areas in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma $ </tex-math></inline-formula> plane where the conductivity of FGMs should lie are determined based on the criteria relevant to the polymeric outdoor insulator under normal and abnormal operating conditions. A new mathematical formula to express the field-dependent conductivity of FGMs is proposed to consider the saturation effect in high-field regions. Two different insulator models equipped with nonlinear resistive FGMs are presented and evaluated under different operating conditions, ac and overvoltages. In addition, the generated resistive loss within the FGMs and the leakage current under power frequency operation are evaluated. Finally, we studied the possibility of using nonlinear FGMs for polymeric outdoor insulators in HVDC systems.

The durability of superhydrophobic and slippery liquid infused porous surface coatings under corona discharge characteristic of the operation of high voltage power transmission lines

Application of polyfunctional water-repelling coatings for high voltage outdoor power lines wires, insulators, and line supports recently gathered large interest due to their ability to substantially boost performance. Such functionalization can mitigate the accumulation of water precipitates and atmospheric pollutions, decrease leakage current, increase flashover and corona ignition voltage. However, harsh conditions concomitant to a high voltage such as high energy ions and electrons, high ozone concentration, UV radiation impose strict requirements on the durability of applied coatings. In this paper, we focus on the analysis of the durability of superhydrophobic coatings (SHC) and slippery liquid infused porous surfaces (SLIPS) under prolonged exposure to industrial grade alternating current corona discharge. Reported results show that in contrast to previously reported low resilience of polymer-based SHC, proper metal-based SHC withstands many hours of exposure without notable degradation. The obtained data on the stability of SLIPS under corona discharge show notable degradation related to the high rate of infused layer depletion. Overall, reported results broaden the understanding of the effect of corona exposure on functional materials and reinforce the optimistic view on the applicability of SHC and SLIPS coatings in the power transmission industry.

Experimental Study and Modeling of the Effect of ESDD/NSDD on AC Flashover of SiR Outdoor Insulators

Pollution flashover occurs when soluble and nonsoluble materials cover the surface of an insulator, and this may ultimately cause a reduction in its performance. In this paper, the common type of sodium chloride (NaCl) was used as a soluble pollutant (ESDD) and kaolin as a nonsoluble pollutant (NSDD). Samples of silicone rubber (SiR) insulators were selected for this study and fabricated at the Advanced High Voltage Engineering Research Centre (AHIVEC) at Cardiff University. The samples were preconditioned and polluted according to standard specifications. Additionally, the AC voltage ramp technique was used to achieve flashover (FOV) voltage with different pollution levels. The aim of this work was to investigate the effect of nonsoluble materials on flashover characteristics to understand their interaction with dry-band arcs by using FOV electrical equations and experimental data. The test results show that the FOV voltage of the silicone rubber insulator substantially decreased with the increase in both ESDD and NSDD values. It was also identified from these results that the dry-band arcs were considerably influenced by both ESDD and NSDD levels. This impact can be quantified by determining the variation of discharge parameters (N, n). Based on the FOV equations and experimental data, a mathematical model was suggested, taking into account the effect of both ESDD and NSDD.

Non-destructive analysis of power insulators by frequency response function and three dimensional-computed tomography

Various techniques are being implemented to analyze outdoor insulators. It plays an important role in the transmission line, and its electrical insulation and mechanical support capabilities must be met at the same time. Mechanical analysis of physical properties and electrical analysis of the threshold voltage to destruction, accounts for a large part. This article focused on detection of pores and crack of insulators by implementing frequency analysis using frequency response function (FRF) an unique non-destructive analysis method, and three dimensional-computed tomography (3D-CT) fault analysis. The purpose of this method is to diagnose insulator defects with non-destructive analysis methods rather than traditional costly breakdown analysis methods. In the case of FRF, the low frequency band stress wave was created up to 35 mm−1 using the Impact Response Test (IRT) using the impact hammer. Due to the difference in the stiffness of the insulator, it moved more than 5.79 μm−1 from the samples B and D that were insulated. For samples, whose insulation was destroyed, a pore size found with 3D-CT was at least 4.88 mm, through which leakage current penetrated The insulating fracture path inside the insulator was formed with a pore diameter of 1.98 to 4.88 mm, through which leakage current penetrates.

Predicting the DC pollution flashover voltage on the insulation surfaces with superhydrophobicity

Cleanliness and desiccative are necessary for outdoor insulation surfaces to maintain the voltage withstand capability especially in humid and polluted operation conditions. Once the voltage withstanding capability of insulation coatings is reduced by contaminant electrolyte, flashover accidents would be easier to happen, causing tremendous economy and energy losses. Superhydrophobic coatings, due to their self-cleaning property, are deemed to have great application potential in maintaining outdoor insulation performance, especially in humid and polluted environments. The water patterns on superhydrophobic coating in humid and polluted conditions are obviously different from those on traditional insulation coatings. Flashover voltage is one of the indices for quantifying insulation strength, while to date it is still unclear whether the commonly-used flashover voltage prediction models based on Obenaus’s theory are still suitable to be applied in the cases with superhydrophobic surface. Here we proposed a facile and low-cost preparation method of superhydrophobic coating. By analyzing the specific surface condition under humid and polluted conditions, and considering the development of arc path, a novel theoretical model for predicting flashover voltage of superhydrophobic coatings is established from the perspective of electric field. The flashover voltage of the synthesized coating as well as Room Temperature Vulcanized (RTV) silicone rubber coating are tested and compared, for investigating the insulation strength on the synthesized superhydrophobic coating, and verifying the accuracy of the proposed prediction model. It is found the synthesized superhydrophobic coating shows self-cleaning property during the wetting and voltage applying process, the flashover voltage of superhydrophobic coating is higher than that of RTV coating, and is affected less obviously by the change in pollution degree, compared with RTV coating. The established model shows better accuracy in predicting the flashover voltage of superhydrophobic coating than the traditional one, with errors of less than 6%. Based on the proposed model, the flashover voltage of polluted superhydrophobic coating surface is positively and negatively related to the volume and the contact angle of the polluted electrolyte droplet, respectively.

Aging Performance of Low-Density Polyethylene/Silicone Rubber Blends Insulators Under Contaminated Conditions

Insulation materials are a vital part of the electrical system in all kinds of high voltage (HV) Transmission lines. Environmental stresses affect the performance of all types of insulation materials over time. Dielectric breakdown strength (DBS), Hydrophobicity, Leakage current, internal partial discharge and volume resistivity are all three degraded parameters in the service environment. The materials stand best in outdoor insulation, with the lowest partial discharge, highest breakdown strength, high hydrophobic, Lowest Leakage current, and highest volume resistivity. Enhancement of these parameters is a potential avenue for many researchers over the period. In this study, low-density polyethene (LDPE) under different nanofillers, including SiO2, TiO2, TiO2@SiO2, with different weight percentages, are used. This study investigates the behaviour of dielectric breakdown strength (DBS), Hydrophobicity and Leakage Current (LC) for 1000h test under contaminated conditions such as High voltage, heat, ultraviolet (UV) radiations, salt fog, humidity, and acid rain.

Influence of corona discharge on the hydrophobic behaviour of nano/micro filler based silicone rubber insulators

Silicone rubber is one of the most used outdoor insulation materials in the last few decades due to its improved performance in contaminated and humid conditions. The improved performance of silicone rubber insulators is due to their hydrophobic nature, however, the organic nature of silicone molecules makes them vulnerable to ageing and degradation. This paper aims at investigating the loss and recovery of hydrophobicity of four different silicone rubber micro/nanocomposites exposed to corona discharge. The samples were exposed to corona discharge generated by pin-plate electrode configuration under AC stress. A series of tests were performed to observe the impact of different electrode-sample gaps and for various periods of corona exposure. The hydrophobicity of samples was measured pre and post corona exposures at various intervals up to 72 h. This time could confirm the hydrophobicity recovery process. Numerical simulations were also performed in COMSOL Multiphysics to investigate the electric fields along the sample surface at different electrode gaps. Experimental results showed that samples recovery time was proportional to the duration of exposure to corona discharge and inversely proportional to the electrode-sample gap. Among all, samples with 2.5% nano-silica as additive showed better hydrophobicity recovery. Simulation results showed that an increase in electrode gap resulted in decreased electric field intensity, hence supporting the experimental outcomes.

Self-Healing Silicones for Outdoor High Voltage Insulation: Mechanism, Applications and Measurements

This paper discusses the state of the art in the application of self-healing silicone-based materials for outdoor high-voltage insulation. Both the dynamic behavior of the dimethyl side groups of silicone rubber and the diffusion of a bulk siloxane to maintain low surface energy are respectively reported as intrinsic mechanisms responsible for the self-healing of silicone rubber. Localization, temporality, mobility, and the type of synthesis are the aspects defining the efficiency of the self-healing ability of silicone rubber. In addition, the deterioration of the self-healing ability with filler loaded into silicone rubber insulation housing composites is discussed. Taking the self-healing property into consideration among the other properties of silicone rubber insulators, such as tracking and erosion resistance, can be a useful design practice at the material development stage. Hydrophobicity retention, recovery, and transfer measurements are discussed as useful indicators of the self-healing ability of silicone rubber. Nevertheless, there remains a need to standardize them as design tests at the material development stage. The paper is intended to shed the light on the hydrophobicity recovery, a key material design parameter in the development of silicone rubber outdoor insulating composites, similar to the tracking and erosion resistance.

Circuit modelling of aged‐polluted polymer insulators based on measured leakage current characteristics

A new equivalent circuit model for aged-polluted polymer outdoor insulators is proposed here. The structure of the model is constructed as such that it can be applied in investigating the effect of insulator aging and dry band discharge intensity on leakage current (LC) characteristics. To implement the capability of modelling aged insulators, the measured leakage currents from laboratory tests on field aged MV insulators with different level of aging and hydrophobicity were examined. Furthermore, the samples were artificially polluted and the corresponding measured leakage currents from laboratory tests were employed as references. The proposed circuit model can consider the effect of pollution by its topology and represents the aging phenomenon of insulator by the changes in the values of its elements. High similarity between test results and model outputs has confirmed model ability to represent aging effect on LC characteristics. Finally, mathematical equations for model parameters in terms of aging level are extracted using curve fitting, in order to predict the age and life-time of polymer insulator.

Experimental Study on the Extinction Characteristics of Secondary Arc Under Different Secondary Arc Currents Near Outdoor Insulator

On the transmission lines, the secondary arc is the arc that remains at the fault point after the short-circuit current is interrupted, which may pose a threat to the stable operation of the power system. In this article, the extinction characteristics of secondary arc near an outdoor insulator under different secondary arc currents are studied experimentally. The secondary arc has different extinction characteristics under different secondary arc currents of 10, 30, and 50 A. The arcing time, length, morphology, diameter, and breakdown voltage of secondary arc are discussed. Experimental results show that, with the increase in the secondary arc current, the arcing time also increases. The development of the secondary arc has stage characteristics. The length of the secondary arc increases steadily in the first stage and fluctuates greatly in the second stage. In addition, during the single discharge in the second stage, the morphology of the secondary arc will change significantly. The breakdown voltage of the upper electrode in the negative polarity is higher than that in the positive polarity, and it is found that this polarity effect is related to the motion of the secondary arc in space. The research results could provide some reference for investigating the physical characteristics and suppression measures of secondary arc.

Investigation on Electrical, Thermal, and Mechanical Properties of Silicone Rubber ATH Nanocomposites

In the present study, investigations have been carried out by choosing the nano-sized ATH (30 – 50 nm) particles as filler content in silicone rubber to acquire a deep insight to understand the use of nano ATH fillers in silicone rubber on its performance, to use it as insulation structure as an outdoor insulator. Variation in the surface condition of silicone rubber nanocomposites due to corona aging and the recovery characteristics analysis carried out through contact angle measurement. Nano ATH added in silicone rubber, up to 3 wt% of filler, shows increased dielectric constant with less loss factor. Water droplet-initiated discharges on silicone rubber nano ATH composites under DC voltage measured using UHF technique and the damage caused zone analyzed through AFM studies and by surface potential measurement, which indicates higher surface roughness and increased charge trap depth. It is observed that negative DC voltage has higher CIV followed by positive DC and AC voltage. Laser Induced breakdown studies (LIBS) show a direct correlation between plasma temperature and material surface hardness. Also, on laser shining on the surface of the specimen, its temperature was measured on the backside of the specimen through thermal imaging confirming increased diffusivity of temperature. Laser flash analysis shows a direct correlation between filler content in base polymer and thermal conductivity and diffusivity. Higher storage modulus and activation energies measured from the dynamic mechanical analysis indicate the significance of prepared composites as an excellent mechanical support structure for the power system network.

Analysis of the Ultrasonic Signal in Polymeric Contaminated Insulators Through Ensemble Learning Methods

Outdoor insulators may experience stress due to severe environmental conditions, such as pollution and contamination. Through the identification of partial discharges by ultrasonic noise, it is possible to assess the possibility of a power grid failure occurring. In this paper, ensemble models are used to analyze an ultrasonic signal from an ultrasonic microphone Pettersson M500. As the insulators are susceptible to developing irreversible failures, it will be evaluated whether the ultrasonic signal will remain over time, so that it is possible to assess whether the discharges being captured can result in a failure in contaminated polymeric insulators, evaluated in a high voltage laboratory under controlled conditions. The ensemble models were used in this paper because they typically require less computational effort than techniques based on deep learning and have acceptable performance for the problem at hand. The bagging, boosting, random subspace, bagging plus random subspace, and stacked generalization ensemble models are evaluated, and the best result of each model is used to compare the differences between the models. The bagging ensemble learning model proved to be faster and have lower error than other ensemble models, long short-term memory (LSTM), and nonlinear autoregressive (NAR).

Analysis of Physical, Ocular, and Aquaphobic Properties of Zirconium Oxide Nanofilms by Varying Sputtering Pressure

A thin coating of zirconium oxide (ZrO2) is placed on outdoor high‐voltage insulators to minimize air fouling. ZrO2 thin film coatings were deposited on glass substrates using a DC sputtering (reactive magnetron) technique with sputtering pressures ranging from 5 to 25 mTorr. Characterization of the deposited films was carried out utilizing approaches such as XRD, AFM, CAG, and spectrophotometer. Following the XRD peaks, when 15 mTorr is reached, the average crystallite size increases, after which it begins to decline. The wettability of the deposited thin layer is associated with the coarseness calculated by AFM. At 15 mTorr pressure, maximum aquaphobic is achieved (107.45°). At this pressure, the transmittance and bandgap were similarly determined to be 90% and 5.43 eV, respectively.

A Study of the Cleansing Effect of Precipitation and Wind on Polluted Outdoor High Voltage Glass Cap and Pin Insulator

In this work, the extent of natural cleansing effect of rainfall, wind and fog or a combination of these on an insulator string were investigated. Results showed that pollution losses progress with time, with a considerable fraction of losses occurring within 15 minutes of testing. While wind alone played little or no role in surface cleansing, it increases the extent of cleansing by rainfall. The topsides of insulators were found to be more affected by natural cleansing compared to the underside. Equivalent Salt Deposit Density (ESDD) and Non-Soluble Deposit Density (NSDD) measurements were carried out. ESDD was found to be higher in the lower disc irrespective of the weather condition the insulator string has been subjected to. NSDD measurements established no pattern on how natural cleansing was impacted by disc position on a string, demonstrating the random nature of pollution-cleansing cycle of outdoor insulators. Insulator performance was assessed by high voltage AC tests and monitoring of partial discharge events using Radio Frequency antennas and a High Frequency Current Transformer (HFCT). Measured output by the HFCT showed that leakage current decreases uniformly with time, and the speed at which this occurs is an indication of the intensity of natural cleansing activity.

Experimental Study on Optimization of Filler Concentration of Silicon Rubber Compound Used in High Voltage Insulators

Abstract: In any power transmission system, insulators are essential for a reliable electrical power supply. The Efficiency of insulators will be decided by their electrical and mechanical properties. Recently in many of the power transmission systems, the conventional porcelain insulators are being replaced by polymeric insulators due to various advantages in their properties. Polymeric insulators have been increasingly popular in recent years as a result of their superior performance in contaminated environments due to their hydrophobic nature. However, research is still being carried out on Polymeric material with regards to ageing condition and feasibility for large scale utilization. Ageing of insulation is due to Environmental, Tracking and Erosion conditions. Ageing leads to immature failures and uncertainty in the performance of the insulators. The constituent materials and their properties have a significant impact on the performance of polymeric insulators. There is a strong need to look into newer filler materials which can be added to the existing polymeric base materials to constitute a composite. Keeping this in mind, in the proposed research uses Silicone rubber as base polymeric material and along with that additives are added to arrive at three different composites. A new filler material will be added to the base material forming a new composite. All these HTV Silicone rubber based composites are then tested the recovery of hydrophobicity, dielectric strength, hardness, specific gravity, tensile strength , ultimate elongation ,tear strength properties based on ASTM standards. Further, Inclined plane Tracking and Erosion studies are also conducted on the polymeric test samples for 6 hours to evaluate the SiR housing material suitability for outdoor insulator applications by subjecting them to AC high voltages under laboratory conditions as per IEC 60587 standards. Keywords: Recovery of hydrophobicity, dielectric strength, hardness, specific gravity, tensile strength, ultimate elongation, tear strength, inclined plane tracking and erosion, ageing, filler material.

Influence of dispersing aids on nano alumina/micro aluminum tri hydrate filled silicone rubber composites for outdoor high voltage insulators

AbstractNano alumina and micro aluminum tri hydrate filled high‐temperature vulcanizing silicone rubber composites were prepared with dispersing aids of surfactant Triton™‐X‐100 (TX‐100) and silane coupling agent 3‐methacryloxypropyltrimethoxysilane (KH‐570), through an in situ modification technique. Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) analysis were carried out to understand the effects of dispersing aids on the structural and crystallographic properties of composites. Scanning electron microscopy images of TX‐100 dispersed composites revealed the presence of several localized regions of agglomeration, whereas KH‐570 dispersed composites showed moderate dispersion. Measurements of volume resistivity demonstrated an increment of four decades for KH‐570 dispersed nanocomposite over TX‐100. Better compatibility between fillers and base matrix through KH‐570 was evident from the low loss factor values. Inclined plane tracking and erosion results were discussed in detail with leakage current analysis. The binary composite prepared with KH‐570 was observed to resist the detrimental dry band arcing and subsequent erosion by 2 h and 20 min over TX‐100 dispersed composite. Dry arc resistance and the formation of thermal pathways connecting micro and nanofillers were discussed in detail. FTIR analysis of ash generated after inclined plane tracking and erosion test confirmed the surfacing of added fillers. KH‐570 dispersed composites showed superior properties as compared to composites prepared with TX‐100.

Viability of Fillers in HTV Silicone Rubber in the AC and DC Inclined Plane Tests

The viability of fillers for inhibiting the dry-band arcing damage on high temperature vulcanized silicone rubber under the critical AC and the equivalent DC voltages of inclined plane test is investigated. Alumina tri-hydrate and ground silica are employed in the study as common fillers employed in silicone rubber formulation for outdoor high voltage insulation, and thermal analysis is applied in order to understand the protective mechanisms of the fillers. Filler volume effect plays a role in improving the erosion performance, and the dilution effect of water of hydration is shown advantageous for preventing progressive (directed) erosion. Dilution effect promoted with internal oxidation is found only notable at 50 wt% alumina tri-hydrate in this study. On the other hand, alumina tri-hydrate at 10 or 30 wt% may yield a porous residue, which is conducive to thermo-oxidation (combustion) and consequently erosion. The erosion suppression effects reported for the fillers in the composites employed in this study are found less viable under the equivalent DC as compared to the critical AC voltages of the inclined plane test. This study clarifies common perceptions about the viability of fillers in silicone rubber for AC and DC outdoor insulation applications.