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Journal ArticleDOI

History and bibliography of polymeric insulators for outdoor applications

01 Jan 1993-IEEE Transactions on Power Delivery (IEEE)-Vol. 8, Iss: 1, pp 376-385
Abstract: A history of polymeric insulators is given, beginning in the 1940s when organic insulating materials were used to manufacture high-voltage indoor electrical insulators from epoxy resins Their advantages and early experiences with them are given A bibliography covering mainly 1970 to the present is given >
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TL;DR: In this paper, the authors present a review 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, low molecular weight components present in the insulators, 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
Abstract: 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.

495 citations

Journal ArticleDOI
TL;DR: Special attention is given to the mechanism of thermal transport, the enhancement of thermal conductivity in polymer nanocomposites/fibers, and their potential application as thermal interface materials.
Abstract: Polymers are usually considered as thermal insulators, and their applications are limited by their low thermal conductivity. However, recent studies have shown that certain polymers have surprisingly high thermal conductivity, some of which are comparable to that in poor metals or even silicon. Here, the experimental achievements and theoretical progress of thermal transport in polymers and their nanocomposites are outlined. The open questions and challenges of existing theories are discussed. Special attention is given to the mechanism of thermal transport, the enhancement of thermal conductivity in polymer nanocomposites/fibers, and their potential application as thermal interface materials.

431 citations

Journal ArticleDOI
TL;DR: In this article, a critical evaluation of the chemical and physical mechanisms responsible for hydrophobicity loss and recovery is presented, where the authors evaluate the properties of silicone rubbers based on polydimethylsiloxane (PDMS).
Abstract: 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 oxida. tion 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.

318 citations

Journal ArticleDOI
TL;DR: In this paper, the fundamental relations between the thermal conductivity and thermal stability of polymer nanofibers and their molecular characteristics were studied by studying the temperature-induced phase transitions and thermal transport of a series of polymers.
Abstract: Polymer nanofibers with high thermal conductivities and outstanding thermal stabilities are highly desirable in heat transfer-critical applications such as thermal management, heat exchangers, and energy storage. In this work, we unlock the fundamental relations between the thermal conductivity and thermal stability of polymer nanofibers and their molecular characteristics by studying the temperature-induced phase transitions and thermal transport of a series of polymer nanofibers. Ten different polymer nanofibers with systematically chosen molecular structures are studied using large-scale molecular dynamics simulations. We found that high thermal conductivity and good thermal stability can be achieved in polymers with rigid backbones, exemplified by π-conjugated polymers, due to suppressed segmental rotations and large phonon group velocities. The low probability of segmental rotation not only prevents temperature-induced phase transition but also enables long phonon mean free paths due to reduced disor...

148 citations

Journal ArticleDOI
TL;DR: In this article, the fundamental relations between the thermal conductivity and thermal stability of polymer nanofibers and their molecular characteristics were studied by studying the temperature-induced phase transitions and thermal transport of a series of polymers.
Abstract: Polymer nanofibers with high thermal conductivities and outstanding thermal stabilities are highly desirable in heat transfer-critical applications such as thermal management, heat exchangers and energy storage. In this work, we unlock the fundamental relations between the thermal conductivity and thermal stability of polymer nanofibers and their molecular characteristics by studying the temperature-induced phase transitions and thermal transport of a series of polymer nanofibers. Ten different polymer nanofibers with systematically chosen molecular structures are studied using large scale molecular dynamics simulations. We found that high thermal conductivity and good thermal stability can be achieved in polymers with rigid backbones, exemplified by {\pi}-conjugated polymers, due to suppressed segmental rotations and large phonon group velocities. The low probability of segmental rotation does not only prevent temperature-induced phase transition but also enables long phonon mean free paths due to reduced disorder scattering. Although stronger inter-chain interactions can also improve the thermal stability, polymers with such a feature usually have heavier atoms, weaker backbone bonds, and segments vulnerable to random rotations, which lead to low thermal conductivities. This work elucidates the underlying linkage between the molecular nature and macroscopic thermal properties of polymer nanofibers, which is instrumental to the design of thermally conductive polymer nanofibers with high temperature stabilities.

118 citations

References
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Journal ArticleDOI
TL;DR: In this article, the authors demonstrate that the abnormally large hysteresis effect observed in advancing and receding contact angles of water on some polymer surfaces can be attributed to the reorientation of hydrophilic moieties of polymer molecules at the surface.
Abstract: The contact angle of a water droplet on the surface of a solid polymer or hydrogel (water-swollen three-dimensional network) depends on whether a hydrophilic moiety of the polymer molecule is oriented towards the air interface or towards the bulk of the solid, but not on the hydrophilicity of the molecule. Therefore, the short-range rotational mobility of a polymer molecule has a major influence on the apparent hydrophilicity of a polymer surface as measured by the contact angle of water. By the came principle, the abnormally large hysteresis effect observed in advancing and receding contact angles of water on some polymer surfaces can be attributed to the reorientation of hydrophilic moieties of polymer molecules at the surface. These factors are demonstrated by selected polymer surfaces with different degrees of mobility at the polymer-air interface.

312 citations

Journal ArticleDOI
TL;DR: In this paper, a theoretical model to determine the effect of dry band discharges on material performance was presented, and good agreement between the predicted behavior and the experimental findings was shown.
Abstract: The materials evaluated in fog produced from low (250 mu s/cm) and high (1000 mu s/cm) conductivity water include cylindrical rod samples of high-temperature-vulcanized silicone rubber and ethylene-propylene-diene monomer rubber (EPDM) containing various amounts of either alumina trihydrate or silica fillers, or both. Comparison is made with material performance results obtained with AC, which was reported in an earlier study. In both low- and high-conductivity fog, the time to failure with AC and +DC was very similar, but a reduction by a factor of about four was observed in the time to failure with -DC. For both AC and DC, silicone rubber performed better than EPDM samples in low-conductivity fog, while the order of performance was reversed in high-conductivity fog. A theoretical model to determine the effect of dry band discharges on material is presented. Good agreement between the predicted behavior and the experimental findings is shown. >

222 citations

Journal ArticleDOI
TL;DR: In this paper, the wettability of aged surfaces and of the bulk of naturally aged silicone and EPDM (ethylene-propylene diener monomer) insulator housings and silicone elastomer insulator coatings was studied.
Abstract: The wettability of aged surfaces and of the bulk of naturally aged silicone and EPDM (ethylene-propylene diener monomer) insulator housings and silicone elastomer insulator coatings was studied. The samples were taken either directly from the insulators or treated by exposing them to corona discharges and/or to saline pollution. The results show that the contact angles of the silicone rubber insulator surfaces are larger than the contact angles of the RTV (room-temperature vulcanizing) silicone rubber coating and of the EPDM rubber insulator surfaces, especially when the surfaces are aged. When the insulators were exposed to corona discharges, the contact angles of the silicone rubber insulators are reduced but after exposure recover with time. The contact angles of the EPDM rubber insulators, however, continue to reduce after the exposure. When exposed to artificial saline pollution, the silicone rubber insulators show a limited recovery of their contact angles with time, while when exposed to corona discharge after saline pollution, they show a recovery of the contact angle after the exposure. The recovery time is dependent on the exposure time to the corona discharges. The EPDM samples do not show any recovery of their contact angles, either when left to rest after the salt deposition or, when after the salt deposition, they undergo a subsequent exposure to corona discharges. Furthermore, such an exposure may be deleterious for the EPDM polymer and the insulator surface may become completely hydrophylic. >

154 citations

Journal ArticleDOI
TL;DR: In this paper, a study on the loss and recovery of hydrophobicity of RTV (room-temperature vulcanizing) silicone-rubber insulator coatings in a salt-fog chamber is reported.
Abstract: The results of a study on the loss and recovery of hydrophobicity of RTV (room-temperature vulcanizing) silicone-rubber insulator coatings in a salt-fog chamber are reported. The results complement those previously reported on the ability of the coatings to suppress leakage current and insulator flashover. The temporary loss of hydrophobicity caused by dry-band arcing and the subsequent recovery are studied in depth. The gradual loss of hydrophobicity as determined from the leakage current and the contact-angle measurements is shown to be related to the physical changes to the coating brought about by dry-band arcing. >

150 citations