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The impact of pollution on insulator surface performance has been extensively studied to continuously improve the insulator performance using suitable condition monitoring, including using the leakage current harmonic component analysis. However, the analysis of harmonic components, particularly in relation to the odd harmonics of the leakage current in aged insulators under the influence of contamination and humidity, is still not fully understood and remains deficient. In this paper, the leakage current of aged and polluted insulators under different environmental conditions are investigated. The study was conducted experimentally using twelve samples of insulators with varying degrees of aging. The crest factor was employed as an indicator of the leakage current index. The findings showed that the odd harmonic crest factor demonstrates high sensitivity in classifying the degree of aging in contaminated insulators. [ABSTRACT FROM AUTHOR]

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Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, a study on a cap and pin insulator (1512L) is proposed to evaluate the distribution of the electric field and the potential along the insulator under different conditions. A computational and experimental study for the examination of a real insulators model is assessed. Tests on contaminated insulators in the laboratory under the suggested conditions have been carried out. Finite element methods (FEM) have been employed in the numerical analysis to assess the electrical properties of the insulator under the suggested contamination profiles, including potential and electric field. The study proposed in this paper provides an effective and practical tool for analysis and enhance the dielectric properties of the studied insulator. [ABSTRACT FROM AUTHOR]

Silicone rubber (SR) samples are coated with various types of artificially prepared pollutants, in order to identify and distinguish them by employing laser induced breakdown spectroscopy (LIBS). LIBS analysis is successful in identifying the elemental composition of the various types of pollutants. The presence of copper sulphate as well as carbon-based compounds such as fly ash, coal and calcium-based compounds such as cement and calcium phosphate (fertilizer) have been identified by the increment in the normalized intensity ratio of the copper, carbon and calcium peaks respectively. LIBS spectral data has been used in conjunction with several machine learning (ML) algorithms such as linear discriminant analysis, decision tree, K-nearest neighbors and various gradient boosting techniques to classify seven different types of contaminated SR samples. When compared to the other ML approaches utilized in the present study, classification using the Light gradient boosting technique has reflected better classification accuracy of 97.43% with a reasonable computation time of 5.1 s.

Railway system insulators are affected by pollution, altitude, and other environmental situations during operation, which causes reduced electrical performance or even flashover accidents. These factors threaten the safety of railway operations in high-altitude areas. However, the natural contamination characteristics of a railroad in a plateau area is still unclear. In this study, a natural pollution accumulation test for railway insulators in a high-altitude area was carried out, and the distribution rules of nonsoluble deposit density (NSDD), equivalent salt deposit density (ESDD), NSDD/ESDD ratio, and nonuniformity (T/B) of the pollution distribution of the tested insulators were calculated. Meanwhile, the chemical compositions of the pollution from different test sites were analyzed. The differences of pollution accumulation between railway insulators and suspended insulators of a power system and the influencing factors were compared and analyzed by combining with a numerical simulation. The results show that the pollution level of railroad insulators is mainly distributed in level b and above. A pollution sample is mainly composed of sodium chloride, while the NSDD/ESDD ratio of pollution is mostly distributed from 0 to 5, with T/B value ranges from 1/0.62 to 1/1.76. The amount of insulator contamination is influenced by the location inside and outside the tunnel. Additionally, the pollution amount is influenced by the structure and type of insulators. Finally, this paper studies the creepage distance and structural height required by railway insulators in a plateau area according to the natural pollution accumulation characteristics of railway insulators, which can provide a reference for a railway electrical external insulation configuration in a high-altitude area. [ABSTRACT FROM AUTHOR]

For the safe operation of the power grid, online monitoring of insulator pollution degree is of great significance to the power system. Considering that the insulator contamination mostly is accumulated in the dry season with little rain, it is very valuable to assess the pollution degree with the small leakage current signal measured at low humidity. To this end, this article analyzed the moisture characteristics of contaminated insulators when the insulator temperature is lower than the ambient temperature and found that the water absorption rate of the contamination layer is proportional to the “apparent humidity” at the interface. Then, an assessment method for insulator pollution degree based on contamination moisture at unsaturated humidity (RH < 100%) was proposed, which has application prospects in arid areas. [ABSTRACT FROM AUTHOR]

Insulator pollution flashover has a high probability in the faults of transmission and distribution system. Due to its complex formation process and various influencing factors, the relevant studies are mostly based on experimental tests and empirical formulas, which do not fully consider the impact of random factors on the flashover process. The quantifiable algorithms are lacking, and it is difficult to effectively predict pollution flashover. In this article, the quantum transition theory is introduced in the streamer theory to calculate the energy-level transition probability of the particle on the surface of polluted insulator. The randomness of particle collision cross section is considered, and the initial discharge voltage is calculated by probability theory. The effects of active particle content, ambient temperature, and relative humidity on the initial charge number of insulator pollution flashover are analyzed. On this basis, the initial discharge process of insulator pollution flashover is studied. The experimental results show that the calculated results of insulator pollution flashover initial discharge voltage based on quantum energy-level transition probability are consistent with the experimental values, which has engineering application value for insulator pollution flashover prediction. [ABSTRACT FROM AUTHOR]

This paper introduces an analytical model of contaminated insulators under critical conditions. The dynamic mathematical model based on the description of the equivalent electrical circuit approach and the criterion for the propagation of discharge has been improved. A few laboratory tests were conducted on practical insulators installed to measure the flashover voltage and determine dynamic arc parameters (A and n). The electric arc constant values are extracted based on the simulation of the experimental results using the genetic algorithm technique with several levels of pollution. The critical parameters, which are the current, length, and resistance of discharge, have been measured and calculated based on the proposed model. The actual results of the proposed models' voltage were compared with the experimental results and previous research study under various resistance of pollution layers. Statistical analysis based on different coefficients were applied to validate the reliability of the proposed models. The experimental and simulation findings show the insulator's expected performance under various operating conditions per the IEC 5070 Standard. [ABSTRACT FROM AUTHOR]

Insulator pollution flashover occurs frequently and is harmful to the power transmission and distribution network. But the randomness of the pollution flashover and the complex influencing factors make it difficult to be predicted. The objective of this paper is to study the mechanism of the discharging on insulator surfaces and design a the calculation method which derives flashover probability. By calculating the distorted electric field in the initial streamer discharge quantitatively and combining it with the equivalent circuit of the insulator surface, the initial discharge voltage is derived. By analyzing the change in power input and dissipation in the process of the arc discharge, we propose the criterion on arc development and extinction, and the critical flashover conductivity of the insulator is obtained. Based on the probability density function, the behavior of the factors on the critical flashover conductivity is described, and the probability of insulator pollution flashover is calculated under different environmental conditions. In the validation experiment, the measured initial discharge voltage and pollution flashover ratio are close to the calculated values. The methods proposed in this paper could be used in the quantitative calculation of the initial discharge voltage and the prevention of the pollution flashover on insulators. [ABSTRACT FROM AUTHOR]

Flashovers seriously affect the safe operation of high-voltage transmission lines. The influence of different pollutants on the flashover of insulators differs greatly. For hygroscopic aluminum phosphate, glucose, and other contaminants, the saturated moisture and flashover characteristics can cause flashovers at low humidity. Therefore, it is of great significance to quickly detect the moisture content in the field. In this article, based on the laser-induced breakdown spectroscopy (LIBS) method, the spectral characteristics of aluminum phosphate contamination were studied, and the spectral lines that characterize the content of aluminum phosphate were obtained. The detection limit for phosphorus was calculated according to the calibration curve. The difference in the moisture content of aluminum phosphate contamination also affects the LIBS signal. The atomic spectrum of phosphorus is selected as the analytical spectral lines. Within a certain relative humidity range, spectral data normalization reduces the influence of the moisture content on the mass fraction of aluminum phosphate samples detected by LIBS. The research results are of great significance for the rapid detection of special contamination, such as aluminum phosphate, in actual lines. [ABSTRACT FROM AUTHOR]

For many years Eskom has followed international guidelines in selecting transmission and distribution insulator products for use in polluted environments. [ABSTRACT FROM AUTHOR]

Insulators are one of the many components responsible for the reliability of electricity supply as part of transmission and distribution lines. Failure of the insulator can cause considerable economic problems that are much greater than the insulator cost. When the failure occurs on the transmission line, a large area can be without electricity supply or other transmission lines will be overloaded. Because of the consequences of the insulator’s failure, diagnostics of the insulator plays a significant role in the reliability of the power supply. Basic diagnostic methods require experienced personnel, and inspection requires moving in the field. New diagnostic methods require online measurement if it is possible. Diagnostic by measuring the leakage current flowing on the surface of the insulator is well known. However, many other quantities can be used as a good tool for diagnostics of insulators. We present in this article results obtained on the investigated porcelain insulators that are one of the most used insulation materials for housing the insulator’s core. Leakage current, dielectric loss factor, capacity, and electric charge are used as diagnostic quantities to investigate porcelain insulators in different pollution conditions and different ambient relative humidity. Pollution and humidity are the main factors that decrease the insulator´s electric strength and reliability.

The flashover of pollution, observed on the insulators used in high voltage transmission, is one of the most important power transmission stakes. It is a very complex problem due to several factors including the modelling difficulties of complex shapes of insulators, different pollution densities at different regions, non-homogeneous pollution distribution on the insulator surface and unknown effect of humidity on the pollution. In the literature, some static and dynamic models have been developed by making some assumptions and omissions to predict the flashover voltages of polluted insulators. This paper aims to experimentally analyse the flashover process and simulation of the distributions of the potential and the electric field under 50 Hz applied voltage on a real model simulating the 175CTV outdoor insulators largely used by the Algerian Company of Electricity and Gas (SONELGAZ). This real model is studied under non-polluted (distilled water), and polluted (distilled water and sand) environments. The simulations were carried out by using the COMSOL multiphysics software. This program uses the finite element method to solve the partial differential equations that describe the field. Experimental results made in the laboratory and simulation results are original and found to be congruent. [ABSTRACT FROM AUTHOR]

Among the main causes of outdoor insulation failures is their poor specifications in terms of leakage distances. This happens when the selected criteria are unable to cope with all the stresses imposed by the changes in environmental pollutions. Therefore, it is important for utilities to fully understand the actual pollution characteristics of the service environment in which the insulators are operating. In this paper, the pollution severity and performance of some 13.2 kV ceramic insulators, sampled in different areas of a Canadian aluminum factory, are assessed. The investigations were performed taking into account the influence of air humidity. Various characteristics were investigated to assess the pollution levels of the insulators, such as equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD), surface resistance, and leakage current characteristics (density, 3rd harmonic amplitude, and phase). It was witnessed that the insulators, collected around the factory, were much more polluted in comparison to the initial expectation. The pollution level should not be considered static due to the environmental parameters’ dynamics. Lessons to learn: the reliability of an electrical grid is dependent on components whose own reliability is strongly affected by external factors, of which there is often a poor awareness. If care is not taken to re-evaluate the post-installation pollution levels of the insulators, the light may simply turn out!

Highlights • Natural pollution components of insulators. • Sources of natural contamination of insulators. • Particle size distribution of polluted surface of insulator. • Contamination of insulator surface varies with height. Abstract In order to study the natural contaminants and sources of ±800 kV DC line insulators, a natural pollution monitoring platform was set up to collect the natural contamination and measure its chemical composition. In this paper, enrichment factor analysis method is used to analyze the surface soluble and insoluble components and sources of insulators, and to compare the difference in contamination between the upper surface and the lower surface of insulators. The results show that the metal cations in the surface contamination of insulators are mainly caused by man-made pollution, and the insoluble components on the surface of insulators mainly come from natural pollution, and the lower surface of insulators are more seriously polluted by humans. In addition, the influence of the height on the surface contamination of the insulator is also studied. It is found that both the equivalent salt deposit density (ESDD) and non-separated deposit density (NSDD) of the de-energized insulator on the tower decrease with the increase of the height, but then decrease slowly. Insulators on high voltage lines are less polluted than insulators on low voltage lines. [ABSTRACT FROM AUTHOR]

Pollution flashover is harmful and has caused huge economic losses. Thus, it is important to evaluate the contamination condition of insulators to prevent the pollution flashover. The objective of this paper is to discriminate the insulator contamination grades by the noncontact method. In this paper, a method of visible light images assisted with infrared information is proposed. The proposed method evaluates the contamination condition using the visible light images, and is corrected by the infrared information in the wet environment. A mathematical model is established to study the relationship between the equivalent salt deposit density (ESDD) (mg/cm2) and the color features. The influences of illumination L and relative humidity (RH) on the color features are analyzed and their eliminated methods are proposed. The infrared image information is proposed to assist the visible light image method when RH ≥ 60%. In the experiment, the visible light images of the artificial polluted insulators are acquired by a digital camera under different illuminations L and RHs, and the average value of V component Vave in the YUV color space is selected for the discrimination of contamination grades. In the test, the proposed method gives an 84% accuracy rate when RH < 60% and gives an 89% accuracy rate when RH ≥ 60%. Finally, naturally polluted insulators were tested. The general test error of ESDD is about 0.0119 mg/cm2. Therefore, it might be concluded the condition of naturally polluted insulators could be evaluated by the proposed method of visible light images assisted with infrared information. [ABSTRACT FROM PUBLISHER]

Energized insulator's surface contamination is greatly affected by its electric field properties. However, few reports about the electric field influencing mechanism on the pollution deposition have been presented. In this paper, the coupling-physics model of a three-unit XP-160 insulator string was established, and the particles' deposition process was simulated by using the finite element method. The effects of the electric field on the pollution particles' motion were analyzed. Research results indicate that the closer to the insulator string, the larger the intersection angle q between the electric force and its horizontal component. The main function of the electric field on insulator contamination is that it changes the pollution particles' vertical moving speed, thus accelerating the particles' deposition process. The particle capture coefficient ratio ck can be used to reflect the pollution degree discrepancy between DC-energized and non-energized insulators. In this paper the ratio ck of the DC-energized to non-energized condition is in the range of 1.04 to 1.98, very close to the field measurement results of the DC pollution ratio k. [ABSTRACT FROM AUTHOR]

This paper is aimed at a systematic study of the leakage current of high voltage polyamide insulator string under different conditions of pollution for possible application in the electric locomotive systems. It is shown that in the case of clean/dry and clean/wetted insulators, the leakage current and applied voltage are linear. While in the case of pollution with saline spray, the leakage current and the applied voltage are not linear; the leakage current changes from a linear regime to a nonlinear regime up to total flashover of the insulators sting. Traces of erosion and tracking of insulators resulting of partial discharges are observed.

The inner area close to cap and pin of insulator is sometimes heavier polluted than the outer area, causing the contamination pattern on insulator surface look like ring-shape. This kind of non-uniform pollution may affect insulator flashover voltage. In this paper, artificial pollution tests of 4 types of porcelain and glass insulators with ring-shaped non-uniform pollution were carried out. Experimental results indicate that the SDD (salt deposit density), the non-uniform pollution degree K (the SDD ratio of inner part to outer part), the heavily polluted area with radius r, and the insulator profile all have significant effects on insulator flashover performance. The effects of K and r on flashover performance can be reflected by the change of pollution layer conductivity during flashover. Under ring-shaped non-uniform pollution, the relationship between Uso and SDD can still be expressed by negative power function, while coefficient a varies obviously with pollution non-uniformity, but exponent n does not. Finally the correction coefficients of flashover voltage considering non-uniform pollution degree K were also calculated for outdoor insulation design. [ABSTRACT FROM AUTHOR]

One of the important factors influencing outdoor insulators performance is pollution phenomenon. The pollution, especially during humidity condition, reduces superficial resistance of insulator and lead to a flow of Leakage Currents (LC) on the insulator surface, which may result in total flashover. The LC characteristics are affected by parameters such as nature and severity of pollution. Location of pollution is another parameter that can be effective. This paper presents the analysis of LC waveforms of insulator strings under different pollution location and Equivalent Salt Deposit Density (ESDD). The tests was performed on the HV porcelain suspension insulator string in which three adjacent discs of insulator string were contaminated and location of them changes along the insulator string. Besides, the effect of humidity and operating voltage on LC waveforms were investigated. Experimental data were analyzed in both time and frequency domain. Obtained results indicate that there is strong correlation between the location of pollution and LC parameters such as peak value ( ), harmonic components and Total Harmonic Distortion (THD). Also, the ratio of fifth to third harmonic component ( ) is presented as an important index that has strong relationship to the pollution location.

Pollution materials affect insulator flashover performance, and there is long-term significance in researching it. In this paper, common kinds of nitrates were used as the soluble pollution, and the ac flashover performance of four types of insulators under different nitrates were investigated. Basing on a large amount of primary data, the calculation of flashover gradient in specific to different pollution materials was discussed, and the effects of nitrates on it were analyzed. Research results indicate that, flashover gradient of insulator under nitrates is commonly higher than that under NaCl; among the nitrates, KNO3 corresponds to lower insulator flashover gradient while Ca(NO3)2 corresponds to a higher one; the exponent b, which characterizing the influence of ESDD on flashover gradient, is lower under nitrites than that under NaCl; for the four insulator samples polluted by nitrates, the flashover gradient of the porcelain type can be expressed by A?ESDD?0.21?NSDD?0.16, the flashover gradient EL of the glass type can be expressed by A?ESDD?0.22?NSDD?0.14, while that of the composite samples can be expressed by A?ESDD?0.19?NSDD?0.13. Research data may provide references for the better prediction of flashover voltage as well as for the better design of external insulation. [ABSTRACT FROM AUTHOR]

The flashover performance of insulators is significantly affected by the degrees and ways of wetting the pollution layer. However, there have only been a few reports on the wetting condition and its effects on the flashover characteristics of pollution on insulators to date. In this paper, a phase-angle difference-based method is proposed to test the wetting conditions of the pollution layer on insulators. A corresponding measuring device is also developed. The wetting process of the pollution layer on aerodynamic-type glass insulators is studied in an artificial climate chamber using the developed device. The related flashover performance is studied via the even-rising voltage method. Test results show that the phase-angle difference (PAD) curve accurately reflects the entire wetting process of the pollution layer from the initial stage, through the saturated stage to the oversaturated and washing away stages. Over the wetting process, the PAD curve initially drops sharply, and then remains stable for a few minutes before eventually rising slowly to the initial value. The PAD curve has its lowest value when the pollution layer is wetted to saturation, which occurs after approximately 5 min in our experiments. The flashover voltage characteristics of insulators are also significantly affected by the wetting conditions of the pollution layer. The flashover voltage in the saturated stage is shown to be lower than that in the other stages. Therefore, to improve the accuracy of the artificial pollution tests, quantitative methods (including PAD) should be used to obtain the exact time of wetting to saturation. [ABSTRACT FROM PUBLISHER]

Previous simulation and observations showed that, the air flow field at windward and leeward side of insulator string will probably be different if the wind velocity is over a certain value, and thus causing the imparity of contamination degree at the two sides. In this paper, fan-shaped non-uniform polluting method was used to artificially simulate the different pollution severity at windward and leeward side of insulator string. Then, the effects of fan-shaped non-uniform pollution on ac flashover performance of 5 types of insulators were discussed. Test results indicate that, SDD, the ratio SDD of windward to leeward side (W/L), the occupation ratio of leeward side (k), will affect the ac flashover performance of insulator string. U50 and SDD still can be expressed by the negative power function. A reduction in W/L from 1/1 to 1/15 would give a decrease about 23% in a value, which causes U50 reducing about 25%, but n value changes little. The correction method proposed by EPRI is also applicable for fan-shaped non-uniform pollution, but has difference. A larger creepage distance of insulator does not mean that the creepage distance utilization rate is higher. Due to the influence of fan-shaped non-uniform pollution, the existing insulation configuration of transmission lines in heavily polluted areas may not satisfy the required insulation margin. The results have certain reference significance for the design and selection of transmission line external insulation. [ABSTRACT FROM PUBLISHER]

Pollution on electrical insulators is one of the greatest causes of failure of substations subjected to high levels of salinity and environmental pollution. Considering leakage current as the main indicator of pollution on insulators, this paper focuses on establishing the effect of the environmental conditions on the risk of failure due to pollution on insulators and determining the significant change in the magnitude of the pollution on the insulators during dry and humid periods. Hierarchical segmentation analysis was used to establish the effect of environmental conditions on the risk of failure due to pollution on insulators. The Kruskal-Wallis test was utilized to determine the significant changes in the magnitude of the pollution due to climate periods. An important result was the discovery that leakage current was more common on insulators during dry periods than humid ones. There was also a higher risk of failure due to pollution during dry periods. During the humid period, various temperatures and wind directions produced a small change in the risk of failure. As a technical result, operators of electrical substations can now identify the cause of an increase in risk of failure due to pollution in the area. The research provides a contribution towards the behaviour of the leakage current under conditions similar to those of the Colombian Caribbean coast and how they affect the risk of failure of the substation due to pollution. [ABSTRACT FROM AUTHOR]

A major consideration for utilities applying composite insulators on overhead lines and substations is the aging of the polymer materials used for insulator housing. Historically, a primary driver for composite insulator development was to achieve a good contamination of flashover and aging performance. However, the application of composite insulators is not only limited to highly contaminated areas since large numbers are now also installed in locations with low contamination severities. The study of the long-term aging and life expectancy of composite insulators in clean environments is, therefore, of fundamental importance. Recent work at the Electric Power Research Institute (EPRI) and STRI has identified water-induced discharge activity as an important aging mechanism in these environments. This paper summarizes the findings of the extensive research carried out by these two organizations to determine a practical limit for the permissible E-field on insulator surfaces for design purposes. The initial work by the EPRI to determine e-field thresholds for water-induced corona, published in 1999, is expanded on the basis of small- and full-scale tests by both organizations to refine threshold levels and determine the influence of insulator parameters, such as hydrophobicity and shed profile. The influence of water-induced corona on the aging performance of insulators is also investigated on the basis of in-service inspections, accelerated aging tests, and natural exposure tests. The implications of this work on the need and dimensioning procedures for grading rings are also discussed. [ABSTRACT FROM AUTHOR]

The type of pollution materials may influence the flashover performance of an insulator. In this paper the pollution flashover performance of a 7-unit insulator string, consisting of typical discs, is determined by laboratory tests while varying the weight percentage of soluble (NaCl and CaSO4) or non-soluble (SiO2, Al2O3 and Fe2O3) materials. When studying the effect of pollution materials on flashover performance, the influence of volume conductivity and equivalent salt deposit density (ESDD) under different weight percentages of soluble materials is firstly investigated, and then the underlying factor, the thermal ionization of pollution materials, is considered. Finally, the measurement results of leakage current under different pollution materials are presented. The research results indicate that the effect by weight of CaSO4 is not as severe as that of NaCl, and the reason is not just its effect on the layer conductivity and ESDD, but its effect on the thermal ionization during the arc propagation process may also be one of the key factors. The fact that a small amount of Al2O3 and Fe2O3 causes the flashover voltage to decrease by 20%, may result from the lower ionization potentials and the higher leakage currents caused by non-soluble materials containing Al2O3 and Fe2O3. [ABSTRACT FROM AUTHOR]

• The scheme of obtaining collision velocity and angle by classical model has never appeared in previous papers;. • The particle removal process is integrated into the fouling model of insulator;. • The criteria of particle deposition and removal are proposed by studying the fouling mechanism;. • The rationality is verified by comparison of model simulations, tests and references. The collision of incident and deposited particle is an important factor affecting the pollution of insulator surface. In this paper, an integrated fouling model is developed, which considers the incident particle deposition and deposited particle removal. By analyzing the formation mechanism of pollution layer, the criteria of incident particle deposition and deposited particle removal are proposed, which are based on energy conversion and force balance respectively. Then the COMSOL simulations are implemented to obtain the collision velocity and angle of incident particles, and the pollution mass density of insulator surface is calculated by combining the developed model. The artificial fouling test is carried out to verify the rationality of the model, which takes a three-unit lxy-160 insulators as the object. The results show that the relative errors of the model and test results range from 20.1% to 23.3% under the conditions of this paper, which can better reflect the actual pollution degree on insulator surface. [ABSTRACT FROM AUTHOR]

Under continuous wind of single direction, the leeward area of insulator string may be polluted more seriously than windward area, making the pollution layer distributes like a fan-shape. In this paper, dc pollution flashover tests of 7-unit XP-70 insulator string with fan-shaped non-uniform pollution were carried out. Then the influence of fan-shaped non-uniform pollution on flashover voltage, flashover process, leeward side surface layer conductivity and surface pollution layer resistance were discussed. Research results indicate that, the ratio W/L of windward to leeward side salt deposit density (SDD) affects the dc flashover performance of insulator string. A reduction in W/L from 1/1 to 1/15 would give a decrease of 28% in flashover strength. Flashover voltage may also decrease when the occupation ratio (T) of leeward side increases from 10% to 30%. Under fan-shaped non-uniform pollution, U50 can still be expressed by a negative exponential function of SDD, and the effect of fan-shaped non-uniform pollution on U50-SDD relationship may mainly lie in changing the proportionality coefficient a rather than the exponent n; discharge path was restricted along the leeward side, which may make the air-gap arc easily formed and benefit the flashover process. [ABSTRACT FROM AUTHOR]

The Rapid Flashover pollution test method (RFO) exposes energized polluted insulators to fog and uses step changes of voltage to identify a minimum flashover voltage. The RFO method reduces test time by a factor of three or more compared to up-and-down voltage application method and is thus time- and cost-effective. In this paper the results from RFO on five ceramic and composite station insulators (line, post and hollow) with median 4.7 m leakage distance are compared closely with duplicate tests using up-anddown procedure. The tests on hydrophobic composite insulators used the preconditioning principles from CIGRE Brochure 555. Full-scale withstand testing of the same five but 420-kV class voltage insulators with median leakage distance 13.3 m are also presented. It is indicated that the flashover test results of RTV-coated station insulators should be specially analyzed and treated. [ABSTRACT FROM PUBLISHER]

The electrical characteristics of contaminated insulators wetted by natural fog are rarely reported at home and abroad. Based on natural fog observations for 4 years at Xuefeng Mountain testing station, the AC flashover performance of three units of polluted insulator strings wetted by natural fog was studied. The results show that there are some differences on the flashover voltage stress between results of field test and Baker et al. The AC flashover process of the polluted insulators mainly includes wetness of the contamination, formation of dry bands, burning and elongation of partial arc and flashover. Moreover, the wind velocity has influence the flashover performance of insulator strings. [ABSTRACT FROM PUBLISHER]

As natural contamination of insulators may lead to flashover, its determining factors should be studied to prevent the occurrence of pollution flashover. In this paper, the fluid mechanics models of insulators with typical shed types were established to simulate their flow field distribution and particle collision coefficient (P). At the same time, a natural contamination test lasting for 8 months was carried out in order to contrast the experimental data and simulation results. The research results have shown that: wind velocity and shed type affect the flow field near the insulators; P is affected by particle diameter and wind velocity; under certain particle diameter and wind velocity, P reaches the maximum value; rainfall has different effects on contamination of insulators with different shed types; wind causes non-uniformly distribution of pollution on the surfaces; the simulation test and the experimental test are comparable. The research method and results can provide not only reference to establishing natural contaminating model but also significant meaning for the external insulation design and selection. [ABSTRACT FROM PUBLISHER]

High-speed airflow, which is generated around trains running at a high speed, causes uneven pollutant distribution on insulator surfaces and changes their insulation properties. In this paper, a method has been proposed to calculate the residual pollutant resistance on polluted insulator. Based on the analysis of flashover model, the influence of pollution distribution along and around insulator was discussed. Analysis result showed that flashover voltage would increase when the pollutant distribution on insulator decreased compared to conditions with uniformly distributed pollutant, and vice versa. It implied that there should be a maximum pollutant accumulation value above and below the insulator shed. In this situation, the flashover voltage will be the lowest. Model analysis showed that the flashover voltage would increase with the length of the insulated plate and vice versa. The theoretical analysis was in good agreement with experimental result, which implied that this method might be able to provide reference for insulator shed design. [ABSTRACT FROM AUTHOR]

Leakage current monitoring is a widely employed technique to monitor the performance of outdoor insulation. The investigation of leakage current waveforms offers significant information since the waveforms' shape has been well correlated with different types of surface activity. Field waveforms are not often considered and investigated due to technical difficulties and the long term monitoring required for recording activity portraying waveforms. Therefore, the basic stages of activity have been defined mostly through accelerated lab tests. However, lab tests do not reproduce exact field conditions and therefore field activity may differ from the one recorded in the lab. In this paper, an investigation of LC waveforms recorded in a heavily polluted site, over more than 6 years of monitoring, is presented. A large variety of waveform shapes are portrayed and various correlations with world experience are made. In addition, recorded data is also investigated in order to identify field related noise. The need for added categorization criteria in the case of field measurements is discussed. [ABSTRACT FROM AUTHOR]

How to decrease the ice on insulators and increase the flashover voltage of iced insulator are hot topics of power system in the world. Many tests have been carried out to investigate whether the permanent room temperature vulcanized (PRTV) coating can change the electrical characteristics of iced insulators both in laboratory and field. Firstly, the test to investigate the icing and electrical characteristic of dc insulator with PRTV coating was carried out. Moreover, comparison has been made between artificial polluted insulator and field polluted insulators. Results indicate that the PRTV coating can not decrease the ice accretion on insulators. Instead, it results in accumulating more ice at the beginning of icing regime, but the influence of PRTV coating will not be remarkable to accumulate ice when there is heavy ice on insulators. . In addition, the PRTV coating can decrease the flashover voltage by 10%. It is also revealed that the flashover voltage for the artificial polluted insulators is lower than that of the field polluted insulators due to the non-uniform of the natural pollution. [ABSTRACT FROM AUTHOR]

High voltage insulators must have high superficial resistance to prevent current conductance in undesired path. In spite of considering appropriate superficial resistance during design and manufacturing, accumulation of pollution on insulators in wet condition along with inappropriate insulation profile design result in electrical breakage and repetitive outages. Operation records, high outage rates due to pollution and short intervals of insulator washing in southern regions of Iran confirm the problem. Thus, appropriate design of insulation in a power network, especially in heavy contaminated regions is very crucial. An efficient and appropriate insulation profile design should be provided based on situation and perfect knowledge of system parameters such us pollution. Insulator profile improvement always considered us one of the suitable approaches to enhance insulation performance in contaminated conditions. In this paper a new approach based on filed measurements of pollution along with simulation is presented to predict insulator performance in polluted conditions. A valuable tool to predict pollution deposition on various profiles to predict insulator behavior and optimum profile in polluted regions is achieved by simulation of weather and dust particles for various insulators surface using fluid dynamic comparing with field studies. [ABSTRACT FROM AUTHOR]

This paper deals with the analysis of partial discharge characteristics of silicone rubber insulators, with the aim to develop a better diagnostic tool to identify the pollution severity of outdoor insulators. In this work, laboratory-based pollution performance tests are carried out on silicone rubber insulators under ac voltage at different pollution levels and relative humidity conditions, using sodium chloride as a contaminant. Partial discharge (PD) is acquired through an innovative PD detection system which is able to collect PD waveforms beside PD patterns. Time domain and frequency domain characteristics of PD pulses at different surface pollution conditions are studied. Statistical parameters of PD patterns are also evaluated in order to achieve a quantitative assessment of pollution severity of polymeric insulators. The results on silicone rubber insulators show that the pollution severity of outdoor polymeric insulators could be identified from the partial discharge pattern analysis. [ABSTRACT FROM AUTHOR]

This article deals with the determination of leakage current and the production of thermal losses on polluted insulators under lightning stresses based on an equivalent electrical model by using Alternative Transients Program (ATP) software. The parameters are varied by thickness of pollution, the ratio of pollution-covered length, and also the steepness of the impulse voltage. The results demonstrate that leakage currents were dramatically increased under different pollution conditions. The consequential mathematical equations show that the rate of leakage current can be controlled by limiting the length and thickness of the pollution layer. Finally, the value of the humidity that is evaporated from the insulator surface as a result of thermal loss can be determined. [ABSTRACT FROM AUTHOR]

This paper presents a two-dimensional (2D) electric fields estimation program to calculate the field distribution along the leakage distance of an insulator under polluted conditions using artificial neural network (ANN). A fog type suspension insulator has been used for calculations. Two types of application are submitted for validation of the model. Firstly, electric fields have been calculated for different line voltages and pollution conductivities using finite element method (FEM). Some of the calculated data sets have been used for training the ANN and the other sets of data have been used for testing. The x, y coordinates and operating voltage have been used as inputs of ANN1 to estimate the electrical fields on the insulator surface for first application. And x, y coordinates and pollution level of the surface have been used as inputs of ANN2 to estimate the electrical fields on the insulator surface for second application. These developed models make it possible to determine the electrical fields easier and shortens the calculation time. The results show that the estimated values of electrical field have been obtained with high levels of accuracy in both models. Thus, presented ANN models can be used efficiently for designing and developing of the insulators for various line voltages and pollution levels. [Copyright &y& Elsevier]

This paper presents an online hydrophobicity measurement technique for silicone rubber (SIR) insulators on transmission lines and its field test results. Based on the hydrophobicity classification (HC) method, an online hydro-phobicity measurement device was developed, which consists of a controllable sprayer, a video camera and a hydrophobicity analyzing software. Online hydrophobicity inspection was conducted for the polluted SIR insulators on three ac transmission lines in the north of China for more than one year by using the device. Some SIR insulators operated for 8 years were analyzed in the laboratory by using the scanning electron microscopy and the infrared spectroscopy. The results show that the surface hydrophobicity of the SIR insulators varies remarkably with seasons. We also find that the microstructure of the pollutants significantly influences the hydrophobic transfer, and that the aging phenomena happen on the surfaces of the weather-shed materials of the SIR insulators operated for 8 year. It is proposed to strengthen the hydrophobicity inspection for the SIR insulators in service. [ABSTRACT FROM AUTHOR]

Insulating links are used to protect crane workers from accidentally contacting a transmission line. This paper presents the results of laboratory tests that determined the leakage current produced by sudden energization of polluted and wet insulating links. Two different manufacturers' links were tested at heavy and light pollution. The results show that the short duration transient or the root mean square (rms) leakage current is the measure of the ability of the links to provide protection. The leakage current can endanger the life of a crane worker before flashover occurs. The dependence of leakage current on test voltage under heavy and light pollution conditions was determined. Obtained leakage current data was compared with IEC 479-1 standard, that provides health effect data. The link protects the crane worker, if the line voltage is less than the maximum voltage determined from the correlated test results. The results were used to assess the efficiency of worker protection. [ABSTRACT FROM AUTHOR]