C. Mayoux

EXPERIMENTAL AND THEORETICAL STUDY OF A GLOW DISCHARGE AT ATMOSPHERIC PRESSURE CONTROLLED BY DIELECTRIC BARRIER

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.

Optical emission due to space charge effects in electrically stressed polymers

Electrical wear-out and dielectric breakdown of insulating polymers involve dissipation to the lattice of the energy of mobile or trapped space charges. Optical emissions are proof of such energy releases and can be used to define the onset of electrical aging and to investigate the dissipation mechanisms. They also could provide a basis for monitoring the degradation rate. The situation considered is that of a material subjected to a voltage stress in the absence of any gas discharge, i.e., the light does not originate from a gaseous plasma. Depending on the type of material and experimental configuration, light emission can be due to excited states of the solid itself and/or of dissolved or adsorbed gas molecules. The polymers of concern are practical materials used as electrical insulation in cables, capacitors, motors, transformers, etc. This review attempts to bring together the published data on electroluminescence of insulating polymers and to discuss the relationship between light emission, space charge, and polymer degradation.

Dielectric breakdown of polyethylene in divergent field: Role of dissolved gases and electroluminescence

The dielectric breakdown of polyethylene subjected to a highly divergent electric field has been studied. The samples were held at room temperature and an alternating field of frequency 50 Hz applied. When the material contained only residual gas it was possible to detect light emanating from the bulk of the polymer. It is proposed that this was an electroluminescence of the polyethylene resulting from the recombination of charge carriers injected at the electrode–polymer interface with the deep trapping centers in the polyethylene. The detection of this light required the use of a very sensitive photomultiplier coupled to an optical microscope. When the material contained a dissolved gas in equilibrium, the behavior of the solid was found to depend on the chemical reactivity of the gas and on its electron affinity. In particular, the influence of oxygen has been studied. A model is proposed which accounts for all the experimental results and which underlines the fundamental role played in the prebreakdow...

Mechanisms of electroluminescence during aging of polyethylene

The study of electrical aging of polyethylene subjected to a 50 Hz ac voltage has shown that electroluminescence occured in the bulk of the polymer. These light emissions (detected in the visible range of wavelength) were due to the buildup of space charge around the electrodes. In a previous paper [J. Appl. Phys. 54, 1532 (1983)] results concerning the role of dissolved gases in polyethylene were presented, where particular attention was paid to electroluminescence effects. The present work aims to answer the two following questions: (1) what are the mechanisms causing the electroluminescence? (2) what is the nature of the luminescent centers? Study of the light emission with respect to the applied voltage form, the frequency, (when ac voltage is applied) and the voltage amplitude, shows that the light emission is due to radiative recombinations of carriers injected through the metal‐dielectric interface following the Fowler–Nordheim effect. This process requires a double injection of carriers. The influ...

Partial-Discharge Phenomena and the Effect of Their Constituents on Polyethylene

A method of investigating partial-discharge phenomena andtheir effect on polyethylene is described. A physical study was carriedout with air at atmospheric pressure and gaps between 2 and 14 mm.It is shown, that with this range of gaps and with dielectric walls, astreamer process appears as in the case of a positive point and a metallicplane.The evolution of the polyethylene samples after the aging producedby the constituents of the discharge, i.e., UV radiation and electronsand ions of low energy, was studied by means of IR spectroscopy. Ifthe discharge is of the streamer type it might be possible to attributethe deterioration to the concentration of ions at its tip; however, IRspectroscopy and scanning electron microscopy have shown thatalthough the ions were more reactive they were not sufficiently so toexplain the damage caused by corona discharges.

A Study of Emission Lines from Electrical Trees

A study has been made of the gases appearing in the channels of bush and branch-like electrical trees propagating in low density polyethylene (LDPE) and cross-linked polyethylene (XLPE) subjected to a strong alternating electric field. The emission lines in the spectral range from 300 to 700 nm were observed with a monochromator and a vidicon tube followed by a multichannel analyzer. These lines, characteristic of the gaseous mixture created by the action of discharges on the channel walls, revealed then presence of CO, C02, and H2. The evolution of these lines was followed as a function of time.

Scanning electron microscope observations of the effects of discharges on polyethylene

The surface of sheets of polyethylene was studied by means of a scanning electron microscope in order to compare the effects of corona discharges and those of the constituents of the discharge, i.e., uv radiation and electrons and O+ ions of low energy. The deterioration produced by the O+ ions resembles that produced by the discharge, and the deterioration produced by the electrons and the uv radiation does not. This difference tends to confirm infrared results and the assumption that the ions concentrated at the tip of a discharge erode the surface of the insulating material.

Atmospheric pressure dielectric controlled glow discharges: diagnostics and modelling

The aim of this paper is to prove the existence of atmospheric pressure dielectric controlled glow discharge and to describe its main behavior. Electrical measurements, short time exposure photographs and numerical modelling were used to arrive at the conclusion. Experimental observations and numerical simulation agreed within a close range. 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.

Towards a better knowledge of insulating polymers under stress

This contribution to a better understanding of insulating materials which are evolving in the domain of electrical engineering, concerns two polymers: a low density polyethylene free of additives, and an amorphous and biaxially oriented poly(ethylene-2,6 dicarboxylate). Through conductivity, dielectric relaxation and luminescence measurements the importance is shown of the role played by the structure of the material on its electrical properties. Also, the evolution of these properties under electrical stress or environmental conditions, such as electrical discharges, are studied.

Influence of aging on electrical properties of polyethylene naphthalate-2,6 dicarboxylate films

Poly(ethylene naphthalate 2,6 dicarboxylate), thanks to its heat resistance, may be used as insulating material in motors and laminated chip capacitors. In these specific applications the occurrence of partial or corona discharges leads to insulation aging and possible breakdown. An experimental investigation has been carried out to determine the changes in dielectric properties as function of the aging conditions, e.g. the temperature of irradiation. Dielectric loss values have been determined in the 10/sup 2/ to 10/sup 6/ Hz frequency range from 150 to 200/spl deg/C. Three relaxation peaks were found /spl alpha/,/spl beta/*,/spl beta/, in the order of decreasing temperature.