An overview of the self-organizing map algorithm, on which the papers in this issue are based, is presented in this article.

The Self-Organizing Map

The aim of this paper is to confirm the existence of atmospheric pressure dielectric controlled glow discharge and to describe its main behavior. Electrical measurements, short time exposure photographs, and numerical modeling were used to achieve this task. Experimental observations and numerical simulation are in good agreement. Therefore, the analysis of the calculated space and time variations of the electric field together with the ion and electron densities helps to explain the discharge mechanisms involved, showing the main role played by the electron as well as helium metastable density just before the discharge is turned on.

Experimental and theoretical study of a glow discharge at atmospheric pressure controlled by dielectric barrier

Barrier discharges, also known as dielectric-barrier discharges or silent discharges, provide a simple technology to establish nonequilibrium plasma conditions in atmospheric-pressure gases. This property has led to a number of industrial applications, including ozone generation, surface modification, pollution control, CO/sub 2/ lasers, excimer lamps, and flat plasma-display panels. Depending on a variety of gas properties, operating parameters, and boundary conditions, the discharge can exhibit pronounced filamentary character, self-organized regular-discharge patterns, or completely diffuse appearance. The literature on these different types of barrier discharges is reviewed, and the underlying physical phenomena are discussed. Relative recent investigations on low-current density diffuse barrier discharges suggest novel applications of fairly "mild" plasmas for sterilization and disinfection purposes and utilizing their selective influence on biological cells.

Filamentary, patterned, and diffuse barrier discharges

An important tool for improving the reliability of HV insulation systems are partial discharge (PD) measurements. The interpretation of such measurements aims at extracting from the measured data information about insulation defects which then are used for estimating the risk of insulation failure of the equipment. Because the physical understanding of PD has made substantial progress in the last decade, it can now be exploited to support interpretation. In this paper a concept is presented which merges the available physical knowledge about various PD types into a generalized model which can be applied to arbitrary insulation defects. This approach will be restricted to PD of the streamer type in gases and at gas-insulator interfaces which cover a large fraction of the cases encountered in technical insulation systems. The generalized model allows us to derive approximate relations between defect characteristics, insulation design parameters and test conditions on one side, and measurable PD characteristics on the other. The inversion of these relations yields rules for extracting defect information from the PD data. The application of the generalized model is illustrated by two simple examples, namely, spherical voids in an insulator and electrode protrusions in SF/sub 6/. >

A generalized approach to partial discharge modeling

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.

Outdoor HV composite polymeric insulators

Molecular structure and electrical behavior

A two-dimensional model of a short-gap breakdown in air is presented consisting of the Poisson equation and the set of conservation equations for electrons, positive ions and stable and unstable negative ions. Recent data on collisional interactions in air are reviewed to determine the transport coefficients, ionization and attachment coefficients and excitation and detachment rates; these are expressed as analytical functions of the local electric field. The conservation equations are formulated in a two-dimensional approximation assuming rotational symmetry. The model is used to study electrical breakdown and discharge formation in a short gap bounded by parallel metallic electrodes at pressures of 1.01, 10.1 and 101 kPa. The results show that at low currents the discharge at all pressures exhibits similar characteristics, typical for a low pressure glow discharges. The calculations were carried out up to the currents of 14.4, 14.3 and 1.35 mA at 1.01, 10.1 and 101 kPa.

Quantitative model of a short-gap breakdown in air

A definite deviation from the Eyring behavior (in fm/T ? 1/T) is found to occur with cable-insulating oils studied over the frequency range extending from 30 Hz to 100 MHz at temperatures between -80° and 27°C. The obtained activation parameters of dipole orientation in the oils exhibit a marked temperature dependence. The results indicate that changes occur in the dipole relaxation mechanism with temperature, and that dipole orientation involves an appreciable rearrangement of the molecules in the neighborhood of the rotating dipoles.

Dipole Orientation in Cable-Insulating Oils

This chapter contains sections titled: Preliminary Remarks Power Cables Communication Cables This chapter contains sections titled: References

Cables: A Chronological Perspective

The frequency and temperature dependence of permittivity and dielectric loss is examined between 0.01 Hz and 1.0 MHz in the range from -50degC to 130degC of a nanostructured composite in an epoxy matrix and compared with that of its constituents (60% quartz and 0.45 % nanoclay by weight). For quartz, which is in powdered form, the variation of permittivity is found to be almost linear with frequency while for nanoclay it exhibits a pronounced increase with decreasing frequency and increasing temperature. In epoxy, the dissipation factor peak magnitude at 10 kHz and 40degC decreases as it shifts to lower frequencies with falling temperature as opposed to that of quartz for which the dielectric losses rise with increasing temperature as the frequency is reduced. When the behavior of the entire nanostructured polymer microcomposite is examined, it is found to exhibit dielectric loss frequency response characteristics similar to that of the microcomposite epoxy-quartz compound without nanoclays, with a marked decrease of dielectric loss with decreasing frequency. Evidently, even a miniscule amount of the incorporated nanoclay (0.45 % by weight) exerts a pronounced effect upon the behavior of the microcomposite. The possibility of a number of dielectric loss mechanisms are considered to account for the observed behavior.

Ray Bartnikas

Papers

Molecular structure and electrical behavior

Quantitative model of a short-gap breakdown in air

Dipole Orientation in Cable-Insulating Oils

Cables: A Chronological Perspective

Dielectric characterization of a nanostructured polymer microcomposite and its constituents