By Topic

Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 5 • Date Oct 1999

Filter Results

Displaying Results 1 - 21 of 21
  • Leakage current and flashover of field-aged polymeric insulators

    Page(s): 744 - 753
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    In this paper results from leakage current (LC) measurements under steam fog and voltage withstand tests under rain conditions obtained on various field aged polymeric insulators are reported. Included in this work are several silicone rubber (SIR) and ethylene propylene diene monomer (EPDM) rubber insulators of ac and dc design that have been energized at suitably high ac and dc voltages under coastal conditions for a period of more than nine years. Their performances are compared to two sets of identical insulators, namely one that was outdoors exposed without being energized and one that was stored indoors. The LC of each insulator was studied three times, namely as received from the field, after it was gently washed to remove soluble pollution, and finally after a voltage withstand test. In between the measurements, the insulators were left to recover for a period of a week. The results show that the LC of the SIR insulators were generally lower than those of the EPDM. In both cases, the LC of the insulators that were stored indoors were significantly lower than those of the outdoor exposed insulators. The voltage withstand tests revealed an almost linear relation between the flashover voltage (FOV) and the arcing distance of the insulators. In general, for similar SIR and EPDM insulators the FOV of the SIR ones were higher than those of EPDM insulators View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Formation and characterization of dry bands in clean fog on polluted insulators

    Page(s): 724 - 731
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    The formation and development of dry bands can best be studied by modifying the standard test procedures. When such controlled behavior is allied with synchronized optical and electrical recordings, then characterization of the pre-formative leakage current, the transient phenomena associated with partial arcs across dry bands, the location of partial arcs and the voltage drop across dry bands can be determined. Interpretation of test data is greatly aided by finite element computation of insulating structures with a conducting surface layer. When this layer is continuous, this allows straightforward prediction of dry band formation under wetting conditions. Following formation, dry bands can be represented by discontinuities in this layer. Simulation of dry bands with various lengths, when combined with the test data, enables partial arc voltage gradients to be quantified. These results will be discussed in the context of previous work on the pollution flashover mechanism of ceramic insulators View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Applications of polymeric outdoor insulation in Japan

    Page(s): 595 - 604
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    Intensive research and development concerning the application of polymeric outdoor insulations in Japan started about 10 years ago. Research on applying polymeric insulating materials 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 View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Development of composite insulators in China

    Page(s): 586 - 594
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    The development of composite insulators in China dates back to the early 1970's. In the 1990's they have become widely used in China. At present, up to 600000 composite insulators are operating on 35 to 500 kV ac overhead transmission lines. They are to be introduced into the ±500 kV HVDC transmission schemes. In China all composite insulators in service are silicone rubber and are operating in various contamination conditions. They have successfully and efficiently avoided serious pollution flashover, which occurred frequently when conventional ceramic insulators were used, and radically reduced the maintenance cost of transmission lines in pollution areas. Study of composite insulators is very active in China. The main aspects include properties of materials such as silicone rubber and fiberglass reinforced polymer (FRP) rods, electrical and mechanical performance, aging as well as evaluation and inspection of composite insulators. These fruitful works greatly promote the development of composite insulators in China View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Flashover mechanism of non-ceramic insulators

    Page(s): 718 - 723
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    The contamination performance of non-ceramic (NC) insulators is better than porcelain insulators. The paper describes the pollution collection mechanism and concludes that silicone rubber insulators collect more pollution than porcelain insulators. Long term exposure of silicone rubber insulators produces a thin layer of pollution, which is a mixture of dust, salt and silicone oil. Fog or morning dew produces droplets on the flat surfaces and forms conductive regions. Spot discharge starts between the regions, which reduces hydrophobicity. Simultaneously, dry-band arcing starts on the shank of the insulator. The two arcs join together, which leads to flashover. The flashover voltage of polluted NC insulators is significantly higher than porcelain ones. Insulator performance is measured with laboratory tests. However, salt-fog and clean-fog tests can give different flashover values View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Outdoor HV composite polymeric insulators

    Page(s): 557 - 585
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2024 KB)  

    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 North 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 View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Review of aging and recovery of silicone rubber insulation for outdoor use

    Page(s): 620 - 631
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (908 KB)  

    This paper surveys the properties which give silicone rubber its distinctive and highly desirable performance characteristics for use as outdoor insulation. The methods of assessing these properties are discussed and this is followed by a detailed survey of what is known of aging and recovery mechanisms. Corona is identified as the principle electrical aging agent and evidence is presented for irreversible loss of polymer as a result of aging. However, the surface recovery mechanisms are robust and, provided there is an adequate resting period, the hydrophobic properties recover. This supports the view, from service experience, that there is no substantial evidence to show that normal aging, unless it results in the exposure of the glass fiber core, detracts from the performance of insulators View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Leakage currents on non-ceramic insulators and materials

    Page(s): 660 - 667
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    This paper presents a review of leakage current (LC) measurements on nonceramic insulators and material samples. It is divided into two parts: First, the field investigations of LC, include a development of LC measuring systems and how the on-line LC measurements correlate to the insulator performance as well as to the atmospheric and pollution parameters. Then, the laboratory investigations, describe how the LC are used to evaluate materials, to develop new testing procedures and to predict insulator performance. An extensive bibliography and additional references is provided View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • RTV silicone rubber coatings for outdoor insulators

    Page(s): 605 - 611
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    The paper presents a review of room temperature vulcanized (RTV) silicone rubber high voltage insulator coatings (HVIC). These coatings are designed to replace greasing and water washing of insulators. Present day coatings are the result of nearly thirty years of development and use. In all but a very few dirty environments, these coatings have lasted ten or more years without maintenance and where maintenance has been found to be necessary, water washing is done at a significantly reduced schedule. The paper focuses on the important characteristics of these coatings and on the rigorous attention that is required in their application in order to ensure good performance View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Acoustic and optical methods for measuring electric charge distributions in dielectrics

    Page(s): 519 - 547
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2016 KB)  

    Much progress had been made during the last two decades in acoustic and optical methods for measuring charge distributions in dielectrics. A review on this topic is given, which mainly covers the past research activities associated with that at our laboratory. For acoustic methods, we will discuss and compare the pulsed electroacoustic (PEA) and pressure wave propagation (PWP) methods and present some of the results that enabled us to gain physical insights into the charge dynamics within solid plate samples and coaxial cables. For optical methods, we will discuss the Pockels effect technique that is used for the dynamic measurement of surface charge distributions, and the Kerr effect technique that is developed for measuring electric field distributions within liquid dielectrics View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hydrophobicity changes in silicone rubbers

    Page(s): 703 - 717
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB)  

    Water repellency, high surface resistivity, vandalism resistance, low density and good processability have made silicone rubbers based on polydimethylsiloxane (PDMS) very attractive materials in housings for outdoor insulation. Their ability to recover hydrophobicity after oxidation or contamination is of paramount importance and this is the topic of this review. A critical evaluation of the chemical and physical mechanisms responsible for hydrophobicity loss and recovery is presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Interfacial phenomena in composite high voltage insulation

    Page(s): 651 - 659
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    This paper deals with two different types of composite insulating materials for HV outdoor insulation technology. For outdoor applications fiberglass reinforced polymer (FRP) is used mainly in transmission line insulators (composite long rods), and as power apparatus housings (composite hollow core insulators). During the last decade mineral filled polymer (MFP) was found to be very suitable for outdoor insulation in the medium and HV ranges. To meet the outdoor demands, long-term stability and durability against environmental stresses are necessary. Composite insulation consists of more than one dielectric component, and linking at least two different kinds of materials leads to interface problems. These regions always appear as weak material structures that can be attacked by various aging mechanisms. The long-term performance and aging resistance are determined by the interface quality. One can distinguish four principal kinds of interface: microscopic, e.g. those between fillers and matrix components; macroscopic, e.g. those between glass fiber rod and polymeric shielding material; internal, in the insulation bulk; and external, solid surface against a liquid or gaseous phase. Today the use of composite insulating materials in HV technology is state of the art. They offer a wide range of superior properties for indoor as well as for outdoor applications. Further improvements should focus on the hydrophobicity and on the long term resistance of the external interface and the stability of the internal interface View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Loss and recovery of hydrophobicity, surface energies, diffusion coefficients and activation energy of nylon

    Page(s): 754 - 762
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    The loss of hydrophobicity of nylon 6/6 caused by immersion in saline water for up to 336 h at different conductivities (0.005 to 100 mS/cm) and different temperatures (0 to 98°C) and its subsequent recovery in air (during 4500 h) have been investigated. The hydrophobicity is determined by measuring the static contact angle θ between the tangent to a droplet of distilled water and the horizontal surface. The changes in the surface roughness and in the weight of the specimens were determined and correlated with the changes in the contact angle. It has been found that θ decreased with increasing conductivity and increasing temperature of the saline solution. After removal from the solution, the higher the conductivity and temperature, the longer it took for θ to recover in air. θ decreased from 70° to 54° after nylon was subjected for 521 h to a uniform field of 15 kVdc/cm in air. The surface free energy of nylon was determined as a function of time of immersion, the conductivity and temperature of the solution and during the recovery in air. The surface energies calculated for the virgin specimen are in good agreement with the literature. The diffusion coefficient of water into nylon increased from 0.23×10-12 m2/s at 23°C to 7.4×10-12 m2/s at 75°C. The activation energy was determined to be 59.4±2.2 kJ/mol. For unaged nylon the surface energies were determined at 23°C to be γS=44.7 mJ/m2, γSD=29.3 mJ/m2, γSH=15.4 mJ/m2, WSL =97.7 mJ/m2 and γSL=19.8 mJ/m2 View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electrical and environmental aging of silicone rubber used in outdoor insulation

    Page(s): 632 - 650
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1172 KB)  

    This is a laboratory study on the aging of SIR and hydrophobicity recovery. UV radiation, corona discharges, acid rain and dry-band arcing are employed as sources of the aging. Chemical and morphological analysis is used to detect the surface chemical and structural changes derived from these stresses. The nature of highly mobile low molecular weight (LMW) chains achieving a quick recovery of the hydrophobicity is carefully examined. Their generation and extinction caused by these stresses are investigated. From this study, it is shown that oxidation that induces crosslinking, branching, interchanging and a formation of silanol groups are the most dominant chemical reactions during the aging of SIR. Furthermore, silanol groups that are byproducts of oxidation restrict the diffusion of mobile LMW chains, which decreases the recovery speed of hydrophobicity and accelerates the aging. A typical aging scenario of SIR from the installation to the end of their life is drawn View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Test methods and results for recent outdoor insulation in Japan

    Page(s): 732 - 743
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    This paper describes new test methods and some typical test results for a recently developed external insulation in Japan. The paper starts with the introduction of the results of the tests that were conducted specially on the external insulation for 1100 kV/10 GW ac transmission line and ±500 kV/2.8 GW dc overhead line section, recently constructed in Japan using heavy duty insulators and giant bushings. Various special tests were made on the external insulation in order to investigate the performance at such high service voltages since those had never been used before, and secondly because of the high reliability required and the importance of the lines. Introduces test methods and some related results on long term performance for the new type of insulators, such as semiconducting glaze and polymer insulators. Also included in the paper are the development of some special test methods and results on line arresters for transmission and distribution lines, which have been accepted widely in Japan View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Monitoring the condition of insulator shed materials in overhead distribution networks

    Page(s): 612 - 619
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Methods of sampling and analyzing the surface material of sheds of composite insulators are reviewed. It is shown that scanning electron microscopy gives useful information from slivers cut from the insulator surfaces, and emission Fourier transform infrared (FTIR) spectroscopy enables derivation of indicators of material oxidation to be developed from surface swabbing with solvents. FTIR absorption spectroscopy and diffuse reflectance FTIR spectroscopy give indicators of surface chalking for ethylene propylene diene monomer (EPDM) insulators. X-ray photoelectron spectroscopy is used to determine surface layer elemental composition and concentration of oxidized bonds. The techniques are applied to field aged 275 kV EPDM and silicone rubber insulators and tentative correlations developed between surface condition and leakage current. Cluster analysis of results from sampling of a large population of EPDM insulators shows that the surface analysis methods facilitate grouping by location and manufacturer View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hydrophobicity loss and recovery of silicone HV insulation

    Page(s): 695 - 702
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    Most of the silicone materials used for HV outdoor insulation are high-consistency, heat cured polydimethylsiloxane (PDMS) elastomers. The unique properties of PDMS that make it suitable for HV applications are reviewed. The surface of these elastomers can be rendered hydrophilic by exposure to discharges. A time and temperature dependent hydrophobic recovery ensues when exposure ceases. A variety of surface characterization investigations have established that corona exposure forms a brittle, wettable, silica-like layer on the surface of most PDMS elastomers. This is consistent with similar effects from oxygen and inert gas plasma treatment. There is still considerable debate as to the relative importance of the two major mechanisms postulated to account for the hydrophobic recovery after corona discharge. The diffusion mechanism invokes migration of low molecular weight species from the interior to the surface, while the reorientation or overturn mechanism envisages a surface reorganization with polar entities such as silanol groups resulting from surface oxidation rotating away and being replaced by methyl groups in the outermost surface layers. In our view, the highly crosslinked silica-like layer cannot reorient readily between hydrophilic and hydrophobic states at the surface, suggesting that diffusion of low molecular weight PDMS components is the more important mechanism of hydrophobic recovery. Recent data obtained on PDMS samples free from low-molecular-weight diffusible species show that hydrophobic recovery may be due to in-situ depolymerization View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Leakage current patterns on contaminated polymeric surfaces

    Page(s): 688 - 694
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    This paper presents measurements of low-level leakage current (LC) patterns on naturally aged insulators and artificially contaminated material samples as well as insulators. A nonlinear behavior of 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 View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Utilization of fog chambers for non-ceramic outdoor insulator evaluation

    Page(s): 676 - 687
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (944 KB)  

    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 View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Test methods for polymeric insulating materials for outdoor HV insulation

    Page(s): 668 - 675
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The paper describes an analysis of standardized and non-standardized test methods for polymeric insulating materials, either suitable or applied for, outdoor HV insulation. The analysis particularly considers the increasing use of silicone elastomers for composite insulators. In the first part, test methods covering erosion/tracking performance and hydrolysis phenomena are discussed. These are inclined plane test (IPT) and arc test (AT) for the evaluation of the tracking and erosion behavior as well as boiling water test (BWT) for the evaluation of the HV diffusion-breakdown-strength. These tests have a long tradition in the field of material research. Secondly, the resistance of hydrophobicity under accelerating aging conditions using simultaneous moisture and voltage stress is considered. Results from the rotating wheel dip test (RWDT) are presented and related to results from an equivalent salt-fog test. The third part of the paper deals with the regeneration of hydrophobicity after sample exposure to moisture and corona discharges. Recovery includes also the transfer of hydrophobicity into pollution layers, which is quantified by measurement of dynamic contact angle View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Survey on the use of non-ceramic composite insulators

    Page(s): 548 - 556
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    This paper summarizes the result of the questionnaire on current status of non-ceramic (composite) insulators in the world conducted by the Non-ceramic (composite) Insulators Technical Committee, Japan. Current use status, reasons for use, maintenance, failure occurrence and research activity of 16 responding utilities are described. About 80% of the responding utilities answered that they would actively increase the use of non-ceramic (composite) insulators in the future. It is anticipated that the market for these insulators will keep expanding View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IEEE Transactions on Dielectrics and Electrical Insulation contains topics concerned with dielectric phenomena and measurements with development and characterization of gaseous, vacuum, liquid and solid electrical insulating materials and systems.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Reuben Hackam