97_spce_varyingvoltage - I EEE Transactions on Dielectrics...

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IEEE Transactions on Dielectrics and Electrical Insulation Vol. 4 No. 6, December 1997 719 Measurement of Space-charge Distributions in Insulators under Very Rapidly Varying Voltage Stephane Hole, Claude Alquie Laboratoire dhstrumentation, Universite Pierre et Mane Curie, Paris, France and Jacques Lewiner Laboratoire d’Electricit6 G6n6rale, Ecole Superieure de Physique et de Chimie Industrielles de la Ville de Paris, Paris, France ABSTRACT In this paper we describe a new instrument for real-time measurements space charge distri- butions in insulators submitted to rapidly varying voltages. It is illustrated with the pressu- re wave propagation method but can also be adapted for use with the pulsed electro-acoustic method. A new acoustic generator has been designed to produce high amplitude pressure pul- ses, at a high rate, and with good reproducibility. This generator, made a thin transducer coupled with a waveguide and a backing medium, responds with a pressure pulse when a step voltage is applied. A special sample holder with a signal decoupling circuit, and a storage unit have been developed. The described instrument allows for measurements at a rate of 3200 Hz. Its potentialities are illustrated by studying the evolution of space charge in polyethylene sam- ples stressed by both pulsed and 50 Hz ac voltages. 1. INTRODUCTION PACE charge phenomena in insulators stressed by a dc voltage can S now be studied by a large set of nondestructive methods [1-61, which have led to the development of various instruments. This allows for themodeling of these phenomena and for the characterization of new insulating materials or structures for HV applications and particularly dc cables. However, electrical energy is mainly transported under ac voltage. In order to investigate space charge phenomena under ac stress, various approaches have been proposed [7-91. The first two methods al- low for the measurement of the charge distribution in the material un- der test. One can be used under very slowly varying voltages (0.1 Hz) [7] whereas the other one uses a sampling of the signal (synchronized measurements) at close points in the phase, but on different cycles [8]. In this last case, several measurements must be done during different periods to obtain the evolhtion of the space charge distribution in one period of the applied voltage. The third method [9] gives only an order of magnitude of the charge transferred at the interface but not the charge distribution. In this work, we describe a new instrument which allows following the evolution of the space charge distribution in insulators in real time during the application of rapidly varying stresses, such as standard 50 or 60 Hz voltages or pulsed voltages. It will be shown that varying signals with a frequency spectrum extending to 1 kHz can be followed. This implies that the time required to measure a single space charge profile must be very short compared to the time scale on which the applied vol- tage varies significantly
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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97_spce_varyingvoltage - I EEE Transactions on Dielectrics...

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