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Silicone polymers are widely used as polymer insulators for housing materials due to their superior properties in the presence of wet conditions and their high electrical properties such as low dielectric permittivity. The hydrosilation reaction (that is the addition of a Si-H bond across a double bond) is used in silicone industry to form crosslinked silicone polymers. In this work silica and aluminum hydroxide were used as reinforcing fillers in order to improve the properties of the material. Investigations about the nature and the amount of reinforcing particles evidence good thermal, mechanical and electrical properties of the composites with an increase of dry arc resistance values twice higher than the unfilled system. POLYM. COMPOS., 35:1253–1262, 2014. © 2013 Society of Plastics Engineers

В статье показана необходимость корректировки действующей в Украине нормативной документации (НД), касающейся выбора и эксплуатации полимерной изоляции, в частности, по вопросу выбора длины пути утечки в загрязненных районах и по обновлению требований к испытательным напряжениям грозового и коммутационного импульса. Рекомендуемые в данной статье скорректированные импульсные испытательные напряжения, а также изоляционная длина полимерных изоляторов позволят обеспечить их более надежную работу в электрических сетях и повысить конкурентоспособность на внешнем и внутреннем рынках. The article shows the necessity of correcting the existing Ukrainian normative documents (ND) relating to the selection and operation of polymeric insulation, in particular, on the choice of the leakage distance in the contaminated areas, and to update the requirements to the test voltage lightning and switching impulse. The article presents the calculated and experimental data voltage pulse discharge in dry conditions and the rain Featured in this article corrected impulse test voltage and insulation length of polymer insulators will provide more reliable work in electric networks and increase competitiveness on the internal and external markets.

Based on the results of basic studies on the housings and FRP cores of polymer composite insulators, a line post type polymer insulation arm for 154 kV with a truss structure formed by three polymer insulation arm units, i.e., two horizontal units with an open angle between them and one suspension unit, was experimentally manufactured. Samples of the polymer insulation arm were tested to verify the withstand voltage performance under polluted conditions, the impulse and power-frequency withstand voltage performance, and the mechanical performance by a full scale test against longitudinal loads.

The silicone-based coating applied to 345 kV post insulators in a substation on the shore of Long Island Sound has depolymerized over a period of about 7 years although no in-service failures have occurred. However, the increasing rate of depolymerization suggests that the coatings will have to be renewed in the near future. This paper reports comparisons of aging and material properties for a number of RTV silicone insulator coatings and measurements related to application of a new coating over an existing, field-aged coating.

This paper presents measurements of low-level leakage current (LC) patterns on naturally aged insulators and artificially contaminated material samples as well as insulaton. A nonlinear behaviorof the LC has been observed. Possible causes for this behavior are discussed and its relations to surface hydrophobicity and electric stress are described. In addition, neural networks are trained to recognize the LC patterns as well as to estimate their harmonic contents.

HV composite polymeric insulators are being accepted increasingly for use in outdoor installations by the traditionally cautious electric power utilities worldwide. They currently represent -60 to 70% of newly installed HV insulators in Nortb America. The tremendous growth in the applications of non-ceramic composite insulators is due to their advantages over the traditional ceramic and glass insulators. These include light weight, higher mechanical strength to weight ratio, resistance to vandalism, better performance in the presence of heavy pollution in wet conditions, and comparable or better withstand voltage than porcelain or glass insulators. However, because polymeric insulators are relatively new, the expected lifetime and their long-term reliability are not known and therefore are of concern to users. Additionally they might suffer from erosion and tracking in the presence of severe contamination and sustained moisture. This leads to the development of dry band arcing that under certain circumstances could lead to failure of polymer insulators. In this paper a review is presented of the recent performance experience of HV composite polymeric insulators in outdoor service, testing methods, aging, the ranking of the materials, the role of fillers, the role of low molecular weight components present in the insulators, the mechanisms responsible for the loss and recovery of hydrophobicity, one of the most important properties of polymers, the mechanisms of failure, detection of faults, type and quantity of natural contaminants, effects of exposure to rain, hydrocarbons, stationary air and wind, various methods to optimize the electrical performance and a relatively new method for evaluating the performance status of polymeric insulators in the field.

Non-ceramic (polymer, composite) insulators consist of a fiberglass core rod, weathershed housing, and metal end fittings. The housings generally are manufactured from polymeric materials. In service, the weathershed materials may be subject to degradation or aging due to harsh environmental conditions. One of the most commonly used laboratory tests to evaluate the performance of the weathershed materials is to employ fog chambers. Design and operational features of various fog chambers are reviewed in this paper, including size and main layout of fog chambers and their HV sources, data acquisition systems, systems for simultaneous visual observations and electrical measurements, and test cycles and techniques.

Intensive research and development concerning the application of polymeric outdoor insulations in Japan started about 10 years ago. Research on applying polymeric insulatingmaterials to power systems covers various fields such as insulators and interphase spacers for overhead transmission lines, polymer housing of bushing and surge arresters for substation apparatus, insulators and interphase spacers for distribution lines and insulators for railways. Polymeric insulators and housings for electric power systems are being evaluated to extend their use, focusing on insulation characteristics such as withstand voltage against salt contamination and deterioration through prolonged use. For railways, trial uses of polymeric insulators have been started on commercial lines.

A new method for measuring the spatial distribution of space charge in polymer insulators has been developed. This frequency method is based on the thermoacoustic signal which propagates into the insulator when a chopped laser beam is focused on the surface of the sample, and will permit a 3D cartography of the space charge.

Polymers are the preferred insulating materials for several electrical applications due to their ease of production, light weight, and low cost. However, their low thermal conductivity constitutes a bottleneck and efforts are made in order to increase it. An approach to improve heat transfer through polymers is the inclusion of fillers with relatively high thermal conductivity. Investigation in this direction has been carried out by different research groups. In this paper, a reference to a number of different studies is made and the role of fillers in polymers is investigated. The main goal of this review is to determine any potential trends which govern and dictate the process of thermal conduction in polymeric composites including nanocomposites and microcomposites.

A general model is introduced for electric conduction in polymer insulation used in high voltage direct current (HVDC) applications. It is shown that for the often occurring case where majority carrier injection is relevant, a generic boundary condition model is unavoidable. Furthermore, the smallness of the conduction current requires to take dynamic polarization into account in a general DC conduction model. Both issues are illustrated with simulation results and experimental observations.

In this work, the Focused Laser-Intensity Modulation Method (FLIMM) is used as a technique for space charge and polarization profiles determination in thin (up to 100 /spl mu/m) polymer layers. This well-known technique is here applied to the study of an electrode-charged polyethylene (PE) and a corona-poled Poly(vinylidene Fluoride) (PVDF) sample. The experimental set-up is first described, and theoretical aspects of LIMM fundamentals are reminded. Then, difficulties encountered during LIMM pyroelectric current deconvolution are discussed, and space charge and polarization profiles are shown.

This article starts from the same points that generated the John Tanaka review, as an homage to his unforgettable contribution to the science of dielectrics and electrical insulation.

Today, after continued development and extensive field and laboratory testing, nonceramic insulators are in use through 765 kV. At transmission voltages, nonceramic insulators have become very popular from 69 through 345 kV. Above 345 kV some nonceramic insulators are in use; however, their usage has not yet become significant. At distribution voltages, confidence in nonceramic insulators is high, so much so that many utilities purchase only nonceramic type insulators. In other utility owned and operated equipment (transformers and their bushings, potheads, surge protective devices, etc.) it is safe to say that the industry has rapidly converted from porcelain to nonceramic wherever the opportunity has presented itself.

This study deals with the investigation on the effect of mineral contaminant and microbiological pollutant on outdoor polymer insulator. An experimental setup using pre-conditioned salt fog test is used to accelerate the desired environmental condition required by the pollutant to grow. As result, the effect of mineral contaminant on the growth of microbiological pollutant in the polymer insulator can be analyzed in a faster manner. Chlorella vulgaris as microbiological pollutant was successfully cultivated on 24 kV polymer insulators in a controlled environmental condition. The analysis is presented by comparing the performances between pre-conditioned and normal insulators. A scanning electron microscope (SEM) test is also performed to determine the growth of chlorella vulgaris. Some leakage current and breakdown voltage measurement tests were conducted to determine the insulation performance of insulators. SEM results show that chlorella vulgaris layer did not grow on the normal insulators. Meanwhile chlorella vulgaris layer was formed up to of 30.5 μm depth inside pre-conditioned insulator surface. The test at 40 kV ac voltage shows up to 0.23 mA leakage current was detected on pre-conditioned insulators. The degradation of breakdown voltage of 12.5 % was detected after 8 weeks treatment.

The vast majority of porcelain distribution arrester failures are the result of moisture ingress. Standards lag technology and do not currently address the unique design aspects of polymer arresters. Traditional sealing test methods cannot be run on polymer arresters because of lack of internal air space. A novel design test is proposed which involves sensitive interfacial leakage current measurements as the diagnostic. Samples are thermally cycled in water to produce thermal excursions and aging, while encouraging water ingress, should the sealing system be compromised. The proposed test is a modification of a protocol established for polymer insulators, which has been correlated to field service. >

The flashover characteristics of the polymer insulator and the effects of a small cavity on the discharge column are investigated. It is observed that the cavity had no noticeable effect on the flashover phenomenon under positive polarity. On the other hand, for negative polarity there seems to be a relationship between the flashover voltage and the needle electrode position away from the cavity opening. It is confirmed that the cavity near high voltage electrode decreases the flashover voltage with negative polarity application.

Charge packets in insulating polymers-especially in polyethylene, have been reported by many groups in different laboratories within the last 15 years. They constitute an unexpected behavior in charge transport and understanding the mechanisms for their formation and propagation could participate in deepening our knowledge of this class of material. Here, we concentrate on "slow packets" modeling. We first recall the general features of the experiments reporting charge packets and the models that have been proposed so far. We then use bipolar transport models featuring injection and transport in an attempt to approach the experimental behavior. The modeling allows discussing the physical situation for packets formation and propagation.

Published work, including mechanistic studies, of molecular dielectrics, involving molecular additives, co-polymers, and miscible and immiscible polymer blends, in the 60s, 70s, and 80s, led to major improvements in breakdown and physical and mechanical properties of polymer-based insulation systems. Many new products were the result of these studies, resulting in improved designs and performance. A comparison is made beteeen these molecular dielectric materials, and new nanodielectrics, to assess each of their advantages and disadvantages. Based on this comparison, potential avenues for improvement of nanodielectrics are identified.

Polymeric insulators used in 13.8 kV distribution network are presenting premature damage due to cavity inner dielectric. With the objective to develop a diagnostic process, it was constructed an experimental distribution line in Universidade Federal de Pernambuco (UFPE) campus. In this article it will be described this experimental line characteristics and performed studies to plan its construction.

Power distribution and transmission networks widely adopt composite insulators for the overhead power line applications. The premature failure of these insulators due to the high electric field induced in them has become a major disappointment in the recent years. In this paper, an 11kV composite insulator is modelled in a three phase high voltage environment, and the induced electrical field is studied using finite element analysis. To reduce the computational time and resources, a simplified geometry for the insulator is also proposed. The electric field calculations are used to understand the importance of using a three phase supply in computational and experimental analysis of insulators, which we determine is more accurate than using a single phase supply.

Polymeric insulating materials with excellent electrical properties are widely used in electrical power equipment. They are degraded however when they are subjected to partial discharges (PD). Factors which control the PD activity include pressure and type of gas present. The pressure variation in a self-contained void will differ from that in voids with channels; also a void with a channel connected to external atmosphere can have the gaseous environment refreshed. A series of experiments is carried out on artificial voids, created from layered sections of polymer. One set of samples has a void inside the polymer with no access to the outer atmosphere; a second set of samples has a void with a closed end channel and a third set of samples has a vent connecting the void to the outer atmosphere. All three sample sets are stressed using the same electrical conditions for the same period of time. Measured differences in PD characteristics and PD induced degradation for the three different arrangements are presented.

Based on the present investigation of leakage current for evaluating and monitoring outdoor insulators, the multiscale nonlinear technique is proposed to analyze the dynamic characteristics of leakage current through the artificial contamination experiments. Contamination tests were conducted in a laboratory by employing heavy salt fog without the deposition of non-soluble contamination. Based on the corresponding relationship between the leakage current and the behavior in heavy-fog conditions, the temporal series of leakage current are extended to two phase space by using a phase-space reconstructed method. In accordance with the dynamic behaviors on the insulator surface, the multiscale entropy of leakage current is obtained to investigate the underlying nonlinear characteristics in relation with the variation of contamination degree, ambient temperature and relative humidity. Associated with the quantitative analysis of mutiscale technique, the results can be helpful to improve the accuracy of insulator monitoring for reducing the accidents.

Electrical trees are defects which can grow in polymeric electrical insulation under high electrical stresses. Their name results from their visual aspect which resembles natural trees. The growth of electrical trees is a precursor to long-term electrical failure; however, the basic mechanism of tree initiation and growth is not yet understood, and remains an important issue for high voltage engineers and equipment designers. In this paper the various techniques used for visualising electrical trees are reviewed and the key research questions concerning the mechanism of tree growth are considered. Optical techniques are mainly used, although electron microscopy adds useful information about the morphology of the defect. Most work has been focused on two-dimensional images. A novel approach using X-ray computed tomography is presented in this paper. The challenges and opportunities for the imaging community are considered. Detailed imaging of incipient trees and sub-micron detail of growth regions hold keys to the mechanisms of growth, but methods such as X-ray tomography need further enhancement to yield useful data.

Polymeric insulating materials with excellent electrical properties are widely used in electrical power equipment. These materials are degraded however when they are subjected to Partial Discharge (PD). Factors which control the PD activity include pressure and type of gas present. When PD occurs in insulation pressure is created and gaseous products changed due to the energy input. A series of experiments is carried out on artificial voids, created from layered sections of polymer. One set of samples has a self contained air void inside the polymer; a second set of samples has a void connected to a channel with closed end; the final set of samples is created with a channel connecting the void to the outer atmosphere. The samples were electrically stressed at 10% above their PD inception voltages (PDIV) under near identical experimental conditions for the same length of time. This paper summarizes a comparative study of the measurements made on PD activity and the chemical and morphological changes occurring on the void surfaces for each arrangement.

The paper is based on the investigative studies performed on the fiberglass crossarm which will be generally used in the distribution line structures as an additional insulation component. Lightning impulse voltage tests were conducted on the fiberglass crossarm alone to determine its critical flashover (CFO) voltage, and also the critical flashover voltage of 15 kV polymer suspension insulator plus the fiberglass crossarm.

Hydrophobic polymer insulators show higher contamination flashover voltages compared with ceramic insulators, but standard artificial contamination test methods have not yet been established. Test methods used for ceramic insulators are now usually used also for polymer insulators, but due to different surface properties and configurations between ceramic and polymer insulators, test procedures and conditions for ceramic insulators may not be pertinent for assessing polymer insulators. Under such circumstances, CIGRE WG C4.303 started round robin tests and results from four laboratories were presented but some differences were obtained.

Techniques used in modeling the electric field (E-field) along an insulator can greatly vary between modelers. This panel session paper will present the challenges faced when multiple modelers attempt model the same transmission line configuration. These challenges also make it difficult to accurately determine the need for a grading ring.

The addition of a corona ring to a polymer insulator will improve the insulators performance, but it must be the right ring used for the right reasons to realize the benefits. A corona ring should not be a quick fix to a problem; it may only mask a bigger concern or delay the inevitable. Selection of a corona ring is as critical a decision as picking the appropriate dry arc, leakage, or mechanical rating for the insulator. Beyond selecting the appropriate size ring for a specific voltage, other critical characteristics include attachment type, mating feature, hot stick-able design, ordering, and packaging.

Hydrophobicity is a prominent characteristic of silicone rubber for polymer insulators. The accurate evaluation on the insulator hydrophobicity is increasingly required for the long-term performance of outdoor insulators in the smart grid. In this paper, based on dynamic dropping test (DDT), acoustic characteristic of surface discharges generated by the dynamic behavior of water droplet was investigated to evaluate the hydrophobic properties of silicone rubber insulator at different ageing levels. The specimens were prepared by using the method of corona degradation and determined by contact angle (CA). It is found that characteristic of discharge sound changing with the decrease of CA. Therefore, the results obtained indicate that the acoustic characteristic of discharge in DDT method is sensitive to the hydrophobic properties, which can be applied as a non-contact method for hydrophobicity evaluation of silicone rubber insulators.

This paper presents the analysis of potential and electric distribution characteristics of outdoor polymer insulator. Silicone rubber provides an alternative to porcelain and glass regarding to high voltage (HV) insulators and it has been widely used by power utilities since 1980's owing to their superior contaminant performances. Failure of outdoor high voltage (HV) insulator often involves the solid air interface insulation. As result, knowledge of the field distribution around high voltage (HV) insulators is very important to determine the electric field stress occurring on the insulator surface, particularly on the air side of the interface. Thus, concerning to this matter, this project would analyze the electric field distribution of energized silicone rubber high voltage (HV) insulator. And the simulation results of electric field and potential distributions along surface of silicone rubber polymer insulators under clean and contamination conditions. For comparative purposes, the analysis is based on two conditions, which are silicon rubber insulators with clean surfaces and silicon rubber insulators with effect of water droplets on the insulator surface. Finite element method (FEM) is adopted for this work. The electric field distribution computation is accomplished using MAT LAB-PDE TOOL software that performs two dimensions finite element method. The objective of this work is to comparison of both the alternative shed and straight shed type insulators under the effect of contamination on potential and electric field distributions along the insulator surface when water droplets exist on the insulator surface

Polyimide (PI) is widely used as insulation in various superconducting power equipments for its excellent dielectric performance and mechanical properties. The cryogenic vacuum is the actual work environment of the insulation systems of superconducting power equipments. Therefore, the study of polyimide film's DC surface flashover characteristics at low temperature in vacuum is of great significance. In this paper, a series of tests for studying polyimide film's DC surface flashover characteristics have been done at temperatures from 78K to 300K in vacuum by using the home-made test system which is developed for testing cryogenic electrical characteristics of dielectrics. The test results show that the surface flashover times and temperature both have some influence on the DC surface flashover strength of polyimide films.

Low current discharges are of concern in the context of predicting the lifetime of outdoor polymeric insulators. The nature of ac surface discharges changes markedly between peak currents of 0.5 mA and 10 mA: the electrical characteristics typically changing from unstable to stable behavior when the peak current increases above 1 mA. This change is important because of the implications of energy transfer between the discharge and the underlying material surface, and resulting changes to ageing mechanisms. In this paper, tests with artificial wind and rain have been conducted to investigate the processes by which unstable discharges become stable. Results show that under the impact of wind and rain, low current (

An insulator in a quenching chamber of a switch causes ablation, and releases gases when arcing. These released gases are known to have an influence on the arc characteristics. In this paper, experiments with the eight kinds of insulators and air will be introduced. The experiments were done by observing the arc shapes changes with digital high-speed video cameras. Furthermore, we measured arc conductance from the quenching peak to current zero by measuring arc voltage and current. The shapes of the arc were observed from two directions.

HVDC technology has been widely used for the bulk power transmission due to its advantages over the conventional HVAC such as higher efficiency with larger current carrying capability and lower electrical losses for long-distance transmission. In this regards, many research institutes have put their intensive efforts to commercialize relevant components in order to realize better HVDC transmission system. One of the critical components for HVDC transmission systems is HVDC polymer insulators which shows rather severe requirements compared to HVAC ones. It has been perceived uneasy to achieve relevant insulation properties with proper design of power apparatus under HVDC. Especially, there is few research works presented concerning the insulation properties of insulator which is a fundamental power component in HVDC system. In this work, dielectric insulation characteristics of various silicone composites have been experimentally investigated under DC stress, of which the results could supply essential base for developing HVDC polymer insulator. For this purpose, polymer composite samples have been prepared in different ways by mixing silicone and ATH respectively and then have been under DC stress to evaluate breakdown characteristics. For the comparison both in DC and AC environment, withstand voltage test and surface discharge test under AC were also performed.

With the spread application of polymer insulators in UHV and EHV transmission lines, the decrease of hydrophobicity becomes one of prominent factors to affect the stability and reliability of power system. Recently, dynamic dropping test (DDT) has been employed to hydrophobicity evaluation, which has proven the occurrence of different discharge phenomena in relation to the hydrophobicity variation. However, limited analysis of discharge characteristics is carried out for the hydrophobicity evaluation by using DDT. In this paper, based on DDT method, the characterization of surface discharges, including the discharge magnitude, pulse number, adjacent discharge magnitude and adjacent time interval, have been analyzed to for the hydrophobicity evaluation. It is found that with the decrease of hydrophobicity, these characteristics of surface discharges apparently show the increasing tendency. The results obtained can indicate that the characterization of surface discharge in DDT method can be utilized to the hydrophobicity evaluation.

The objective of the research is to find (1) The characteristic of surface leakage current of the polymer insulator under the artificial multi stress, (2) Investigating the tropical climate factors which could influence of the surface leakage current of the polymer insulator, (3) The most influential climate factor towards the characteristics of the surface leakage current of the polymer insulator, (4) A comparison of the surface leakage current of the polymer insulator with a ceramic or a glass insulator if they were used in the area tropical climate. The methods used were making design concept of chamber construction and it accessories, designing it, so it could be well functioned and useful. The tests are carried in several stages and the result of the research reveals that the characteristic of the surface leakage current of polymer insulators SIR is much smaller and more stable than ceramic insulator and glass insulator. The test, by blowing the various artificial tropical climate pressure, indicates that the surface leakage current of the polymer insulator SIR is very small for all types of the tropical climate impacts and the smallest comparison occurs when it is blown by the pollution of salty fog in which the average comparison achieves 1 ∶ 3.14 ∶ 4.26 towards ceramic and glass insulator. The difference of the lowest leakage current reaches the average of 72.03 % towards the ceramic insulator and 58.21% towards the glass insulator.

Submitted by Ruth Quaresma de Freitas (ruth_quaresma@hotmail.com) on 2019-04-02T16:26:21Z No. of bitstreams: 1 WARNER PEIXOTO PINHEIRO BARROS - DISSERTAÇÃO PPGEE 2011..pdf: 3373877 bytes, checksum: 0e570ed04a3c8fe91125cf0bf14dd894 (MD5) Made available in DSpace on 2019-04-02T16:26:21Z (GMT). No. of bitstreams: 1 WARNER PEIXOTO PINHEIRO BARROS - DISSERTAÇÃO PPGEE 2011..pdf: 3373877 bytes, checksum: 0e570ed04a3c8fe91125cf0bf14dd894 (MD5) Previous issue date: 2011-06-10 Os isolamentos elétricos são submetidos a campos elétricos e estresses cada vez maiores, devido à diminuição de distâncias elétricas e redução da quantidade de materiais empregados nos equipamentos. Campos elétricos intensos geram corona nas superfícies das partes metálicas provocando a degradação de superfícies isolantes, principalmente, daquelas constituídas de material orgânicos, como os isoladores poliméricos. Ainda não existe um consenso sobre quais níveis de descargas corona são aceitáveis na superfície dos isolamentos. Por outro lado, a intensidade do corona também é afetada pela degradação dos isolamentos orgânicos. Assim, a parametrização das medições das intensidades do corona pode ser usada para se determinar a retirada de isoladores poliméricos de operação, em estado avançado de degradação. Para tanto, técnicas de inspeção utilizando medições de descargas parciais (DP), em laboratório, e de radiação ultravioleta (UV), emitidas pela descarga corona foram avaliadas. As imagens UV foram processadas, visando obter apenas a região de ocorrência do corona em termos de concentração de píxeis. Uma correlação entre níveis de DP e dados obtidos a partir da câmera UV (pontos de descarga/minuto) e, do processamento de imagens (concentração de píxeis do corona) foi realizado. Dessa forma, a técnica de quantificação do corona utilizando processamento de imagens foi implementada, na qual níveis de corona aumentam de acordo com o grau de poluição e degradação dos isoladores para pequenas variações de umidade relativa do ar. The electrical insulation are submitted to electric fields and stress increasing, this occurs due to decreased electrical distances and reducing the amount of materials used in equipments. Corona generates intense electric fields on the surfaces of metal parts causing the degradation of insulating surfaces, especially those made of organic material such as insulators. There is still no consensus on what levels are acceptable corona discharges on the insulating surfaces. Moreover, the intensity of the corona is also affected by degradation of organic insulators. So, the parameterization of the measurements of the intensities of the corona can be used to determine the removal of polymeric insulators operating in an advanced state of degradation. For this, inspection techniques using measurements of partial discharge (PD) in the laboratory, and ultraviolet (UV) light emitted by the corona discharge were evaluated. The UV images were processed to obtain only the region of occurrence of the corona in terms of concentration of píxeis. A correlation between levels of PD and data obtained from the UV camera (discharge points / minute), and image processing (concentration of píxeis in the corona) was performed. Thus, the quantization of the corona technique using image processing was implemented, in which corona levels increase with the degree of pollution and degradation of insulators for small variations in relative humidity.

The objective of this article is to assess polymeric insulators subjected to polluted environments. The case studies were conducted on polymeric insulators installed on 500 kV lines. All analyses were carried out with computer simulations, employing finite element methods to calculate the voltage distribution on the surface of the insulators, and the Rizk model in order to assess the discharge voltage of these components, with deposits of pollution layers. The article also presents a number of problems that occur with polymeric insulators, and which have led to the failure of these units, causing great concern to the electricity sector regarding the system. Important conclusions have been obtained, which contribute to the assessment of these events.

The behavior of the deposited droplet and the movement of the droplet under residual charge on the polymer insulator surface were investigated. It was observed that the deposited droplets after application of voltage tended to move toward the insulator neck. In addition, the distance of the movement toward the insulator neck depends on the applied voltage, the set positions of the droplet and the polarity of the applied voltage. It is suggested that the droplets concentrate around the neck of the polymer insulator so that it might accelerate the wetting process.

This paper presents results of properties of Silicone Rubber (SiR) and Ethylene Propylene Diene Monomer (EPDM) insulation study, e.g. ageing, hydrophobic when they are under polluted dust in Thailand with ozone, UV and temperature. The results showed that the insulation resistance of SiR and EPDM under low ozone environment were sharply and significantly decreased in the first three days no matter they were exposed to various kinds of polluted condition or they were original. When the duration of ageing was prolonged, the insulation resistance trends to be reduced. In addition, the insulation resistance of SiR and EPDM under high ozone environment were slightly lower than that of low ozone environment. The insulation resistance of SiR under UVA, UVC and temperature at 30 °C and 50 °C were significantly decreased in the first three days when they were exposed various kinds of polluted dust including original. When the duration is prolonged the insulation resistance trends to be reduced. The insulation resistance of EPDM when under UVA, UVC and temperature at 30 °C and 50 ° C were slightly decreased during the first 3 days. When the time is prolonged, the insulation resistance remains constant.

In recent years, the concerns about premature failures of polymer insulators have been increasing. These failures, in part, can be attributed to the high electric field (E-field) magnitude at end fittings of these insulators, which may lead to partial discharges activity. The E-field values recommended by manufacturers and researchers, to avoid this phenomenon, are not fully consensual yet, particularly when considering the insulator under service conditions, because the E-field can be affected by several factors. This paper analyzes the E-field along polymer insulators through computational simulations using finite element method to model the insulator and water drops. In association with the simulations laboratory, experiments were performed, where the corona voltage inception was observed. The experiments were made to reproduce moisture conditions on the insulator surface. The results clearly show how certain service conditions may increase the E-field.

In order to identify possible shortcomings at design and manufacturing level, polymeric insulators are subjected to various tests at the laboratory established in ANSI C29.13-2000 [1] and IEC 61109-1995 [2] norms. One of these are environmental, which is done via simulations in laboratories, but these never become so severe and demanding as the present conditions of operation in the field. Therefore, this research develops a methodology to evaluate different designs of polymeric insulators (silicone rubber) suspension type with galvanized steel hardware, aluminum and polymer coated in a natural environment. For this, a specific area was available where environmental conditions are the most severe on the west coast of Zulia State, located north of the Venezuela Guajira, and establishing it as a Natural Laboratory. As a result recommendations were established for the characteristics of polymeric insulators to be used in the distribution network in the Zulia region, in order to obtain the highest reliability through the useful life.

For many years glass and porcelain have been the dominant insulation materials for our bushes, insulators and circuit breakers. Recently however, the situation has changed and we now see outdoor circuit breakers at very high voltages of the order of hundreds of kilovolts using polymeric insulation. The advantages of polymeric insulation have always been known but their tracking performance in highly polluted environments has been disappointing, until now. As manufacturers engage in fierce competition to produce the new generation of insulators, the question of quality and reliability in performance becomes an overriding one. There several tests that have been prescribed by standardization bodies to assess the quality of insulation among them the IEC Tracking Test, the Inclined Plane Test [5] and the Dust Fog Test. In this the authors will start with a brief description of the chemical structures of polymeric materials. They will then discuss the Inclined Plane test based on the American Standard D2303. Further, it will describe the design and operating performance and future prospects of a test set that is suitable for rapid and reliable testing of insulator samples that may be of interest to a manufacturer.

An experimental study was conducted, using a Rotating Wheel Tracking and Erosion Tester (RWT) with the aim to compare the aging performance of different insulators under AC and DC (both polarities) excitation. The procedures of the standard were adapted to perform AC and DC (both polarities) tests on 6 practical insulators from different manufacturers, representing different materials and specific creepage distances. The results obtained confirm the extreme severity of the test, especially for the silicone rubber insulators. The DC tests turned out to be more severe than the AC tests. The formation of a brown deposit on the insulator surface was observed and investigated.