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In selecting adequate insulators for substations at distribution and transmission voltage levels, special measures may be needed in locations exposed to freezing conditions. This first part of the paper describes the environmental and insulator parameters that influence the risk of flashover on station insulators exposed to freezing conditions. Index Terms--Climate, contamination, flashover, fog, high voltage, ice, insulator coordination, snow, station insulators.

In locations exposed to freezing conditions over the station service life, additional measures for selecting adequate station insulators at distribution and transmission voltage levels should be taken. This second part of the paper describes the selection process and mitigation options, based on the environmental parameters, as discussed in Part I. These include insulator size, shape, surface material, surface quality, electric field improvement, and orientation. Index Terms--Climate, contamination, flashover, fog, high voltage, ice, insulator coordination, snow, station insulators.

Test methods for evaluating flashover voltage of ceramic and nonceramic insulators under ice, snow, and cold-fog conditions are recommended. The paper describes the procedure to be followed at various stages of an evaluation test including preparation of the test object, insulator precontamination, ice, snow, and cold-fog deposits as well as voltage applications and flashover voltage evaluation. Some relevant parameters for ice accretion, flashover voltage evaluation, artificial pollution, and power source requirements are taken tram IEC 60129, IEC 60507, and IEEE Std.-4-1995 on standard techniques for high-voltage testing. Index Terms--Contamination, flashover, fog, high voltage transmission, ice, insulator, snow, statistical interpretation, test methods.

This paper presents the results of round robin tests performed to evaluate the electrical performance of Room Temperature Vulcanizing (RTV) silicone rubber coatings used for improving the contamination performance of outdoor ceramic insulators. The tests, performed in six different laboratories, included several salt-fog chambers and a tracking wheel. Most test facilities were equipped with an on-line data acquisition system for measurement of leakage current activity. Four generic formulations of RTV silicone rubber coatings applied on ceramic rods were evaluated. The results indicate a general consensus in the ranking of the coatings' leakage current suppression capability, despite the variation in the experimental conditions employed. This suggests that guidelines for a laboratory test for evaluating the RTV coating material's electrical performance under contaminated conditions could be developed. Key Words: RTV coatings, accelerated aging, erosion, leakage current, water repellency.

This paper addresses the problem of stress calculation and optimization in a FRP (Fibre-glass Reinforced Plastic) pultruded rod crimped into a metal end-fitting. This type of assembly is used mainly for suspension and line post insulators. We discuss herein some aspects that merit consideration in any given design approach. In many respects FRP pultruded materials are anisotropic. The anisotropy of their elastic constants influences the distribution of stresses while the anisotropy of their mechanical properties (ultimate strengths) limits their load carrying capacity. Finally, the anisotropy of their failure modes governs the progression and the spread of the damage. Each level of anisotropy will be discussed distinctly.Geometrical considerations are also necessary to arrive at an efficient design. Namely, we will consider the frictional interactions between the end-fitting inner wall and the rod, then we will present our approach in selecting the appropriate LID ratio (i.e., the ratio of the end-fitting length over the rod diameter), and finally we will discuss the influence of the compression profile, i.e., the permanent radial displacement imparted to the rod due to the action of the crimping force. [ABSTRACT FROM PUBLISHER]

The results and analysis of surface resistance measurements performed on nonceramic insulators (NCI) are presented in this paper. The goal of this study was to determine if the surface resistance measurement procedure can be formalized to ensure repeatable and reproducible results. The NCIs evaluated had housing materials made from one type of silicone rubber and one type of ethylene propylene diene terpolymers (EPDM) rubber. A porcelain post insulator was used as a reference. The Task Force concluded that it is possible to establish a standard for surface resistance measurement in the laboratory. Such a standard is valuable since surface resistance provides: 1) an indication of aging on NCI housing material and 2) a more sensitive indicator of true contamination severity on insulators than provided by conventional ESDD (equivalent salt deposit density) measurements. As a first step in this direction, guidelines for measurement have been provided in this paper. Suggestions for future work needed for standardization are also included in the paper. Index Terms--Aging, contamination, hydrophobicity, nonceramic/composite insulators, surface resistance.

This paper presents an experimental investigation conducted to determine the influence of parameters such as the ambient temperature, pollution level, and substrate material on the formation of dry bands on polluted layers. To investigate these parameters, we applied a simplified insulator geometry, developed in our previous work, to experimentally control the complex process of dry band formation on a polluted surface. The simple geometry of the experimental model enabled the use of Plexiglas, RTV, and glass as construction substrate materials. RTV and glass were used to simulate a composite and ceramic insulator surface, respectively. Moreover, an electrooptic (EO) probe enabled the measurement of the axial E-field evolution at the surface of the dry band during dry band formation. The results indicated that the substrate material, ambient temperature, and pollution level substantially influence dry band formation. The effects of the first two parameters are directly associated with heat transfer phenomena in the substrate material and at the ambient air/substrate interface. The effect of the third parameter is associated with absorption and evaporation of the pollution layer. In addition, the appearance of the dry band can be clearly identified by a rapid increase in both the pollution layer resistance and the axial E-field in the dry band area. The value of the axial E-field is influenced primarily by the width of the dry band and by the pollution layer resistance, which is directly dependent on the humidification duration. Finally, because most of the results obtained herein were in accordance with those in the literature, we conclude that the proposed experimental model may provide an effective and inexpensive testing method for developing new materials and solutions for improving the dielectric performance of insulators used in polluted environments. Similarly, the simple geometry of the experimental model and the ability to easily control the experimental parameters may enable this tool to validate the results of various numerical models in studies of the thermoelectrical behavior of polluted insulators. [ABSTRACT FROM AUTHOR]

Power transmission lines in Ethiopia are experiencing an alarmingly high frequency of unexplained outages triggered by environmental factors, which significantly undermine the reliability of the country's power system. This paper presents investigations aiming to identify those among the unexplained fault records that have been caused by pollution induced flashovers. An identification method is developed, which associates the contextual fault features, such as information about the characteristics of the fault, fault location, and time of day, as well as month of its occurrence with local meteorological/climatic and environmental conditions. A total number of 4231 unexplained faults, recorded between 2015 and 2022, were analyzed. Among them, 1045 faults (24.7%) were identified as being most likely caused by pollution induced flashovers. The entire network suffered from more than 130 pollution-induced flashovers annually with a frequency of about 0.8 faults/100 km/year. The fault frequency strongly differed among the grid regions, being highest in the Northeast and lowest in the Southwest region. Moreover, the performed analyses also concentrated on the evaluation of the pollution performance of various insulator types employed in the network. The results indicate that porcelain insulators have the highest pollution-induced flashover intensity of 1.47 faults/year/1000 units, followed by silicone rubber polymeric composite insulators and glass insulators with the respective intensities of 1.21 and 0.83 faults/year/1000 units. These results indicate that despite the high expectations towards the pollution performance of silicone rubber polymeric insulators, their use in the Ethiopian climatic and environmental conditions appears to be unsatisfactory. [ABSTRACT FROM AUTHOR]

This study aims to enhance the productivity of high-voltage transmission line insulators and their operational safety by investigating their failure mechanisms under ultimate load conditions. Destructive tests were conducted on a specific type of insulator under ultimate load conditions. A high-speed camera was used to document the insulator's failure process and collect strain data from designated points. A simulation model of the insulator was established to predict the effects of ultimate loads. The simulation results identified a maximum first principal stress of 94.549 MPa in the porcelain shell, with stress distribution characteristics resembling a cantilever beam subjected to bending. This implied that the insulator failure occurred when the stress reached the bending strength of the porcelain shell. To validate the simulation's accuracy, bending and tensile strength tests were conducted on the ceramic materials constituting the insulator. The bending strength of the porcelain shell was 100.52 MPa, showing a 5.6% variation from the simulation results, which indicated the reliability of the simulation model. Finally, optimization designs on the design parameters P1 and P2 of the insulator were conducted. The results indicated that setting P1 to 8° and P2 to 90.062 mm decreased the first principal stress of the porcelain shell by 47.6% and Von Mises stress by 31.6% under ultimate load conditions, significantly enhancing the load-bearing capacity. This research contributed to improving the production yield and safety performance of insulators. [ABSTRACT FROM AUTHOR]

Ice accumulation on glass insulators is likely to cause faults such as flashover, tripping and power failure, which interfere with the normal operation of the power grid. Accordingly, superhydrophobic coatings with great anti-icing potential have received much attention. In this study, three superhydrophobic coatings (PTFE, Al2O3 and SiO2) were successfully prepared on glass surfaces by using one-step spraying. The microscopic morphology, wettability, anti-icing and anti-glaze icing properties of the superhydrophobic coatings were comparatively analyzed. The results indicated that the PTFE coating had a densely distributed rough structure, showing a contact angle of 165.5° and a sliding angle of 3.1°. The water droplets on the surface could rebound five times. Compared with the Al2O3 and SiO2 coatings, the anti-icing performance of the PTFE coating was significantly improved. The freezing time was far more than 16 times that of glass (4898.7 s), and the ice adhesion strength was 9 times lower than that of glass (27.5 kPa). The glaze icing test in the artificial climate chamber showed that the icing weight of the PTFE coating was 1.38 g, which was about 32% lower than that of the glass. In addition, the icing/melting and abrasion cycles destroyed the low-surface-energy substances and nanostructures on the surface, leading to the degradation of the anti-icing durability of the PTFE coatings. However, the PTFE coating still maintained excellent hydrophobicity and anti-icing properties after UV irradiation for up to 624 h. The superhydrophobic coatings prepared in this work have promising development prospects and offer experimental guidance for the application of anti-icing coatings on glass insulators. [ABSTRACT FROM AUTHOR]

The research and application progress of resin-based composite materials in the field of electrical insulation has attracted considerable attention and emerged as a current research hotspot. This review comprehensively summarized the research and application progress of resin-based composite materials in the field of electrical insulation, providing detailed insights into their concept, properties, and preparation methods. In addition, a comprehensive evaluation of the electrical insulation performance, mechanical properties, and thermal properties of resin-based composite materials was presented, along with an in-depth analysis of their current application status. Despite the immense potential and development opportunities of resin-based composite materials, they also face several challenges. This review serves as a valuable reference and resource for researchers in related fields and aimed to promote further research and application development of resin-based composite materials in the field of electrical insulation. [ABSTRACT FROM AUTHOR]

The high-voltage (HV) assets in the existing power transmission network will experience increased electrical, thermal, environmental and mechanical stresses and, therefore, robust condition monitoring is critical for power system reliability planning. Fibre Bragg grating (FBG) sensors offer a promising technology in HV applications due to their immunity to electromagnetic interference and multiplexing capability. This paper reviews the current technology readiness levels of FBG sensors for condition monitoring of transformers, transmission lines, towers, overhead insulators and power cables, with the aim of stimulating further development and deployment of fibre-based HV asset management systems. Currently, there are several reported cases of FBG sensors used for condition monitoring of HV assets in the field, proving their feasibility for long-term use in the power grid. The review shows that FBG technology is versatile and can facilitate multi-parameter measurements, which will standardise the demodulation equipment and reduce challenges with integrating different sensing technologies. [ABSTRACT FROM AUTHOR]

The icing on overhead transmission lines is one of the largest threats to the safe operation of electric power systems. Compared with other security accidents in the electric industry, a sudden ice disaster could cause the most serious losses to electric power grids. Among the numerous de-icing and anti-icing techniques for application, direct current ice-melting and mechanical de-icing schemes require power cuts and other restrictive conditions. Superhydrophobic coating technology has been widely focused for good anti-icing properties, low cost and wide application range. However, the special structure of curved transmission lines, complicated service environments, and variated electric performance could significantly limit the application of superhydrophobic anti-icing coatings on overhead transmission lines. In particular, superhydrophobic surfaces can be achieved by combining the rough micro-nano structure and modification agents with low surface energy. Compared with superhydrophobic coatings, superhydrophobic surfaces will not increase the weight of the substrate and have good durability and stability in maintaining the robust structure to repeatedly resist aging, abrasion, corrosion and corona damages, etc. Therefore, this review summarizes the theoretical basis of anti-icing behavior and mechanisms, influencing factors of anti-icing properties, potential techniques of superhydrophobic surfaces on transmission lines, and, finally, presents future development challenges and prospects of superhydrophobic surfaces in the anti-icing protection of overhead transmission lines. [ABSTRACT FROM AUTHOR]

Insulator diagnostics is still a topical issue. No one has yet found out how to accurately determine the condition of all insulators and decide when replacement or maintenance is required. Insulators are one of the main components of a transmission and distribution system and must withstand high voltages in all weather conditions. Moisture and dirt are the main factors influencing the insulating properties of insulators. This article deals with the effect of pollution on a porcelain insulator. An Omicron MI 600 measuring system monitors the changes in the dielectric loss factor and leakage current in a wide frequency range (10 Hz to 1 kHz) to evaluate the contamination level. We applied three high voltage levels (5 kV, 7.5 kV, and 10 kV) to the porcelain insulator to monitor changes in the mentioned quantities with various frequencies. The measurement results confirmed the usability of the dielectric loss factor and leakage current for the diagnosis of insulator pollution. The dielectric loss factor showed more promising results than the leakage current. [ABSTRACT FROM AUTHOR]

In contrast to other transportation systems, railway systems feature special characteristics, which may cause specific hazards to birds. Among other things, there is the risk of electrocutions resulting from short circuits. To protect the birds and minimize these short circuit events, the DB Netz AG has installed so-called animal deflectors on the insulators of the overhead lines. Since this effort, the number of short-circuit events in the respective sections has decreased, according to DB Netz AG. The principal mechanism of action of the animal deflectors is based on mechanical defense, combined with electrostatic discharge on contact. Although the number of short circuit events has been reduced by using animal de- flectors, the detailed function of the animal deflector in different environmental conditions has not been investigated up to now. This research project aims to determine whether, and to what extent, the use of animal deflectors in retrofitting overhead lines may contribute to bird protection and which currents can be measured at retrofitted insulators under different environmental conditions. Hence the current should be measured when using animal deflectors on railway overhead lines for different isolator states and body resistances (5 kΩ, 3 kΩ, 1kΩ, 0.5 kΩ). The results show an influence of measured current depending on the insulator state. Our preliminary results indicate that the use of an animal deflector (KTA) to the tested polymeric insulator and pollution severity can be recommended, since, based on the investigations, no danger to small birds and small animals can be identified. However, the use of the animal deflector (KTA) for the tested porcelain insulator and pollution severity should not be recommended as they showed high animal hazards during pollution and fog conditions. However, these results cannot be transferred to other different insulator types and pollution severities. Investigating the electrical current to the type of insulator used and the expected pollution severity is recommended. [ABSTRACT FROM AUTHOR]

The problem of contamination in ceramic insulators was found to be frequent in power transmission lines and transformers. The key aim was to develop aquaphobic zirconium oxide (ZrO2) thin films using DC reactive magnetron sputtering over glass insulators to mitigate contamination problems. This was achieved by introducing O2 and Ar gas in the sputtering chamber, and three properties, namely, structural, optical, and aquaphobic, were inspected by changing the sputtering gas ratio (oxygen/argon). These properties were chosen based on comparison with the bulk ZrO2. These deposited ZrO2 samples were identified by X-ray diffractometer (XRD), atomic force microscopy (AFM), UV-Vis-NIR spectrophotometer, and contact angle goniometer (CAG). For all the samples, coatings were found to be limpid, clear, and aquaphobic. Coarseness (62.813 nm) and the contact angle made by water to the surface (107.45°) were found utmost as deposited at 0.25 oxygen/argon gas ratios. The transmittance and band gap were also found to be 90% and 5.33 eV, respectively, at this particular ratio. [ABSTRACT FROM AUTHOR]

Pipeline suspension bridges may experience ice accretion under special atmospheric conditions, and the aerodynamic characteristics of the bridges may be modified by the ice accretion. Under some specific climatic conditions of freezing rain, the dependencies of the ice size and shape on the icing duration and some structural properties (including pipeline diameter, inclination angle of wind hanger, inclination angle and size of section steel, and girder geometry) were experimentally investigated in a refrigerated precipitation icing laboratory. Typical ice accretions on pipelines, wind hangers, section steels, and girders of pipeline suspension bridges are summarized. Then the effects of some selected ice accretions on aerodynamic force coefficients of a bridge girder were further investigated through wind tunnel tests. The ice size and shape on the pipeline were closely related to the pipeline diameter and icing duration. The engineering geometric models of ice accretion on pipelines were extracted. The ice shape and size on wind hangers and section steels changed with their inclination angles. The aerodynamic force coefficients of a girder with ice accretion were much higher than those of an ice-free one. The results can provide references for simulating the ice accretion and further evaluating the effect of ice accretion on the aerodynamics of pipeline suspension bridges. [ABSTRACT FROM AUTHOR]

In this contribution, a mathematical model is proposed to predict the discharge inception voltage on polluted insulators under a non-uniform field of a high-voltage DC system. The present study is derived from the modified Peek's law used for predicting the threshold voltage of a typical corona discharge. An onset criterion useful for practical electrode geometries was experimentally validated by considering insulators' level of pollution along with the electro-geometrical parameters including inter-electrode distance, HV electrode radius, and width of the ground electrode. It was observed that the proposed mathematical model is much precise for smaller electrode radii and inter-electrode distances with higher conductivity of the pollution layer. Since prediction of the electrical onset on a polluted surface is of general interest for designing HV equipment suitable for heavily polluted regions in the world, it is hoped that the results presented can be viewed as a benchmark and a challenge for further research. [ABSTRACT FROM AUTHOR]

The increase in recent power failures, with negative impacts on humans and the economy, has been largely attributed to environmental effects and the aging of the power network. These have been accelerated in the last years due to two main factors: an increased load on the power network and material degradation owing to the presence of environmental pollutants. These factors together with specific weather conditions create the incipient conditions for power network degradation. In this paper, a review of the influence of environmental factors on high-voltage (HV) materials and components is provided. Sensing and artificial intelligence (AI) technologies developed to prevent the failure of the material structure and HV components are also reported. [ABSTRACT FROM AUTHOR]

In this paper, an anti‐thunder composite insulator combining an arrester and an insulator is developed and applied to 10‐kV distribution line. The anti‐thunder composite insulator is divided into an insulation section and a lightning protection section. The flashover performance of the anti‐thunder composite insulator and an ordinary composite insulator under ice accretion conditions are experimentally analyzed. The relationship between the icing thickness (d) and the flashover voltage is derived under the contaminated condition of 0.25 mg/cm2 salt density. With the increase of d, the effect of icing on the breakdown voltage of the anti‐thunder composite insulator is less than that of an ordinary composite insulator. When d increases from 2 to 12 mm, the breakdown flashover voltage of the anti‐thunder composite insulator and the ordinary composite insulator drops by 40.0 and 61.9%, respectively. Based on the simulation model, the potential and electric field distribution of the anti‐thunder composite insulator are analyzed. Our simulation and experimental results indicate that the proportion of the potential of the insulation section is more than 90% under the rated voltage. Based on the analysis, it is concluded that the anti‐ice flash performance of the insulation section has an important influence on the flashover performance of the anti‐thunder composite insulator and that an appropriate increase of AC reference voltage of the anti‐thunder composite insulator will be an effective method to promote the stability of the internal zinc oxide varistor under ice accretion conditions. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Optimum structural design of composites is a research subject that has drawn the attention of many researchers for more than 40 years with a growing interest. In this study, a review of the literature on this subject is presented. The papers are classified according to the type of the composite structure optimized in those studies, the loading conditions, the objective function, the structural analysis method, the design variables, the constraints, the failure criteria, and the search algorithm used by the researchers. [ABSTRACT FROM AUTHOR]

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With the adoption of composite insulators in the field of high voltage transmission, it is essential to focus on its safety performance. Our study paid attention to the extensive heating within HV ending of 500-kV AC composite insulators in southern China with high level of humidity and proposed corresponding countermeasures. Via superficial examination, IR and UV test, interface quality inspection, chemical analysis and water absorption test and etc., we were able to study the defected insulators. According to our observation, insulators were slightly covered with pollutants and maintained superficial hydrophobic properties. The heating performance of HV ending of insulators was closely related to humidity as well as the type and site of loading voltage. We suggested that when exposed to high humidity, polarization of the molecules from water, polar groups of material and the interlayer resulted in the abnormal heating; on the other hand, when the environment humidity was low the heating was attributed to partial discharge. Consequently, we provided several solutions toward the issue according to our observations. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]