J.F. Hall

Bio: J.F. Hall is an academic researcher from Electric Power Research Institute. The author has contributed to research in topics: Accelerated aging & Epoxy. The author has an hindex of 3, co-authored 4 publications receiving 279 citations.

History and bibliography of polymeric insulators for outdoor applications

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 >

Accelerated aging and flashover tests on 138 kV nonceramic line post insulators

Abstract: The behavior of 138 kV nonceramic line post insulators is investigated by means of clean fog tests conducted before and after aging in a specially designed accelerated aging chamber. The laboratory aging cycles are justified on the basis of actual weather in the coastal regions of Florida. Analytical measurements quantifying the degree of artificial aging are discussed, and artificial aging is compared with service experience. Observations of audible noise and radio influence voltage during the clean fog tests are reported. >

Rain and contamination tests on HVDC wall bushings with and without RTV coatings

Abstract: Results of tests made to determine the ability of room temperature vulcanized (RTV) silicone rubber coatings to improve the performance of HVDC wall bushings are described. The behavior of uncoated full-scale +or-500 kV wall bushings is first determined in wetting conditions consisting of nonuniform rain and fog with various amounts of predeposited surface contamination. Parameters affecting flashover performance, such as polarity, rain conductivity, and contamination severity, are discussed. Results of nonuniform rain tests on an RTV coated wall bushing are reported. Fog tests and in-service experience have demonstrated that RTV coatings improve the HVDC contamination flashover performance of station post insulators; no flashovers occur in laboratory clean fog tests at rated voltage with ESDD levels up to 0.1 mg/cm/sup 2/. The application of RTV, silicone grease, or oily coatings makes the surface of a wall bushing sufficiently hydrophobic to prevent flashovers during nonuniform rain tests without a pre-deposited layer of contamination. >

Accelerated ageing chamber for non-ceramic insulators

Abstract: Electric utilities are using nonceramic insulators to a greater extent to retrofit existing transmission lines, and consider them viable options for use on sections or entire lengths of proposed new lines in the United States. This increasing acceptance and use of nonceramic insulators was not always the case, however. (Author)

Outdoor HV composite polymeric insulators

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.

Thermal Conductivity of Polymers and Their Nanocomposites.

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.

Hydrophobicity changes in silicone rubbers

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.

Aging of nonceramic insulators due to corona from water drops

Abstract: The fundamental principles of water drop corona as an aging mechanism for nonceramic insulators are presented. It is demonstrated that water drops in the sheath regions enhance the electric field and may cause corona which can play an important role in long-term performance. Electric field enhancement caused by water drops in different locations on the shed and sheath are demonstrated by means of electric field calculations and small scale experiments. The threshold magnitude of the surface electric field for corona from water drops is presented for two silicone rubber surfaces having different hydrophobic properties. The effect of water drop corona activity on the properties of the surface material is shown using small scale aging experiments.

Aging in silicone rubber used for outdoor insulation

Abstract: A hypothesis for aging produced by dry band arcing in silicone rubber material used for outdoor insulation is presented and experimentally proven. Aging is indicated by permanent changes. The analytical techniques used to study the permanent changes are Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and surface roughness measurement. The authors highlight the fact that there are permanent changes occurring in the material that lead to progressive degradation in the long run, even though there can be a complete recovery of surface hydrophobicity in a short time. >