97_laurent_spchg - IEEE Transactionson Dielectrics and...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
IEEE Transactions on Dielectrics and Electrical Insulation b1.4 No. 5, October 1997 585 Optical Emission due to Space Charge Effects in Electrically Stressed Polymers C. Laurent, F. Massines, and C. Mayoux Laboratoire de Genie Electrique, Universite Paul Sabatier, Toulouse, France ABSTRACT 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 ma- terials 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. 1. INTRODUCTION OLYMERS play a significant role as insulating media because of P their excellent physical and chemical properties. They are non- ideal semi-crystalline or amorphous materials containing impurities, structural and chemical defects, interfaces between crystalline and amor- phous units. All these factors contribute to material charging: impuri- ties can dissociate electrically, interfacial polarization occurs at domain boundaries, structural and chemical defects act as trapping sites. In most applications, a voltage is applied to the electrodes which act as a charge reservoir. Charging also occurs in electrodeless configurations when dielectrics are exposed to gaseous discharges or particle beams. Space charge effects are therefore impossible to avoid in practical insu- lation and they influence the short and long term performance of solid dielectrics [l]. Material charging and its consequences are the problems addressed by many contributors to this issue [24]. Space charges have been recognized as harmful for dc applications; they also play a lead- ing role in long term electrical degradation of polymers under ac stress. The underlying problem is to understand how space charges are related to aging and breakdown in order to be able to monitor the relevant pa- rameters for the improvement of system viability and for designs of high reliability, Due to the emergence of several new techniques, an increas- ing interest in the spatial distribution of space charges and its relation- ship with aging and breakdown has been noticed recently [5].
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 19

97_laurent_spchg - IEEE Transactionson Dielectrics and...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online