From the editor's desk

Abstract

In this issue we have three articles. The first, "Dielectric Spectroscopy Techniques as Quality Control Tool: A Feasibility Study", by Bouaicha , Fofana and Farzaneh from the Universite du Quebec a Chicoutimi, and some German and French collaborators, is concerned with the feasibility of using time and frequency domain dielectric spectroscopy to monitor the fabrication of oil-impregnated-paper (OIP) condenser bushings. So what is time domain dielectric spectroscopy? It involves measuring the current flowing in an insulator following application and removal of a dc voltage step. Following voltage application the current decays with time, typically as t <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-n</sup> , where 0 < n < 1, and the measurement is continued until the current reaches a nearly constant value, or, more likely, the experimenter runs out of patience and opts to take the current flowing at a specific time as the nearly constant value. Measurements may extend over several hours, depending on temperature and applied field strength. A value for the dc conductivity of the sample can be estimated from the nearly constant current. The long decay leading to quasiequilibrium yields the dielectric response function, about which much has been written and upon which several scientific careers have been based! Theoretically, the current flowing after the voltage is removed, that is, after the sample is short-circuited, should be identical with that flowing during voltage application, after the appropriate shift of t = 0, subtraction of the quasi-equilibrium current, and polarity reversal. The related frequency domain spectroscopy involves the study of ac currents as a function of frequency, the analysis leading to values for the real and imaginary components of the relative permittivity, ε;.